Munich Apartment Heat Pump Transition

Key Takeaways

Hold the gas boiler in service, upgrade fabric and hydronics first, then electrify the Munich block with a hybrid air-source cascade.

• Defer the 2027 fuel switch and renovate fabric first. Insulate roof/top deck, then outer walls, basement soffit and coordinated glazing, overhaul pumps, balancing and heating curve, then prove ≤55°C flow across cold days ^[3][15][6]. Revised federal rules let the 2004 boiler keep running through 31 December 2044, freeing time for this sequence ^[41][46][49]. Vaillant cases place the later buffered outdoor-air cascade retaining gas peaks near €125,000 gross ^[13][8][12]. KfW programme 458 grants 30% base aid and Munich FKG adds 15% on eligible heating costs ^[35][34][40].
• Swallow higher build cost to secure cheaper heat. Schmidt comparison and Taptaphome data place gas condensing at €8,000-€15,000 against air-to-water at €15,000-€42,000 with single-family turnkey near €36,000 ^[5][12][13]. At 18,000 kWh demand, air-to-water needs about €1,285 yearly against €2,034 for gas because each kilowatt-hour drives several heat units, yet 55°C flow lifts power use versus 35°C and 65-70°C pushes seasonal performance toward 2.0 ^[5][12][26].
• Oversize or overheat and savings evaporate. Heizungsfinder and reduco data track seasonal performance sliding from around 3.0 at 55°C toward 2.0 at 70°C with power use rising 2-2.5% per extra degree ^[26][6][1]. Order main works before KfW approval or skip listed-expert confirmation and grants lapse ^[9][35][38]. Heating uplifts then cap at €0.50/m²/month within six years after 15% maintenance and grant deduction ^[48][32][39].
• Treat references as guides, not guarantees. Evidence suggests the €125,000 illustration reflects a 20-unit case, versus your 24-flat 1,900 m² block where per-dwelling caps split evenly ^[13][39]. One Schmidt report suggests tariff math assuming ~30 ct/kWh, factors above 3 and carbon climbing from the €55-€65/t corridor toward EU-wide building-heat pricing from 2027 ^[5]. One KfW update notes grants depend on available budget ^[38]. Commission a heat-load calculation and multi-day low-temperature trial before sizing ^[6][10][26].

[!WARNING] Pushing an oversized cascade into leaky radiators at 65-70°C collapses seasonal performance toward 2.0, doubling power draw and wiping the gas saving ^[26][6][1].

Abstract

Hold the 2004 gas boiler in service, cut load through roof, façade, glazing, cellar-ceiling and hydraulic upgrades validated at 55°C flow in reduco, HSH and Heizungsfinder guides ^[6][10][26], then add an approximately €125,000 ambient-air cascade retaining gas for peaks with federal and Munich grants, following Vaillant, Viessmann and Reduco multifamily references ^[8][13][16].

Heizungsfinder, reduco, HSH tie outcome to flow, not brand ^[26][6][10]. Prove ≤55°C over several cold days with thermostats open and balancing tuned as HSH, reduco and Heizungsfinder describe; miss that threshold and electricity use climbs about 2–2.5% per extra degree ^[6][10][26]. Effizienzhaus-online, reduco and Lenzenergieberatung place roof or top-floor ceiling first, then façade, cellar ceiling and windows together, then heating plus ventilation, because coordinated connections avoid bridges, condensation and rework while shared scaffolding trims expense ^[3][15][25].

Reduco costing with Vaillant and Viessmann references frames central air cascades at €40,000–€80,000 before aid, near €125,000 fully loaded with buffers and backup, shown by three 10 kW air-to-water units for 30 kW ^[13][8][16]. Devices fetch €5,000–€15,000 and €11,000–€27,000 installed in EnBW, Enter and reduco comparisons, forcing two to five parallels of 7.3–9.7 kW units beyond 100 kW ^[11][33][1]. Gas condensing stays cheaper to buy at €8,000–€15,000 versus €15,000–€42,000 for air-to-water in Energie-Beratung Schmidt, Taptaphome and Reduco figures ^[5][12][13]. Buderus, Thermondo, waermepumpen.info confirm drilling penalties ^[14][17][2]. Probes cost €6,500–€11,000, €50–€75 per metre to 100 m plus water-authority permits per Buderus, Thermondo and waermepumpen.info ^[14][17][2].

KfW product 458 pays 30% BEG base grant of eligible heating costs for all owners including landlords after the 21 July 2026 restart ^[9][35][36]. ADAC, Energie-Fachberater and reduco cap frames per dwelling, split equally centrally, yielding €64,500 on €215,000 for 20 units or €37,500 on €125,000, with total public aid capped at 60% ^[24][39][40]. Munich, Energie-Spezialisten and EMA confirm top-up strings ^[34][42][43]. The FKG adds 15% for electrically driven pumps in buildings over 10 years old and claws back that base if any flat claims federal speed or income bonuses, per Munich, Energie-Spezialisten and EMA ^[34][42][43]. Viessmann, Bundesregierung and Gesetze-im-Internet confirm the revised GEG scrapped the 65% duty from late July 2026, letting the 2004 boiler run to 31 December 2044 with rising green-fuel shares and €50,000 fines, while Munich's November 2025 heat plan stays orientational ^[41][46][47].

One comparison by Energie-Beratung Schmidt suggests 18,000 kWh heat costs €1,285 air-to-water versus €2,034 gas, since one power unit moves several heat units ^[5]. Schmidt, Heizungsfinder, reduco track steep factor drops ^[5][26][1]. It slides from 4.0 at 35°C (€1,500 yearly at 30 ct/kWh) to 3.0 at 55°C (€2,000) and 2.5 at 65°C (€2,400), while carbon climbs €45/t to €55–€65/t with EU trading from 2027, per Schmidt, Heizungsfinder and reduco ^[5][26][1]. Modernisierungsumlage allocation levies 10% yearly after 15% maintenance and grant deduction when subsidised, against 8% unsubsidised, but the €0.50/m² monthly cap throttles collection, per EWI, Vaillant and Energiewechsel FAQ ^[48][49][50]. One Reduco costing suggests only a 20-unit proxy ^[13]. Order a heat-load calculation and low-temperature trial before spending, per reduco, HSH and Heizungsfinder ^[6][10][26].

Table of Contents

Key Takeaways Abstract

1. Introduction
2. Background
3. Findings 3.1 Heat Pump Retrofit Costs for 1972 Munich MFH 3.2 Building Envelope and Heating Prerequisites for Heat Pumps 3.3 Federal BEG and Munich Subsidies for MFH Heat Pumps 3.4 GEG Obligations and Munich Heat Planning Deadlines 3.5 Electricity Versus Gas Operating Costs and Payback 3.6 Tenant Cost Pass-Through Under Modernisierungsumlage Rules
4. Discussion
5. Conclusion References

1. Introduction

A private owner in Munich holds a 1972 concrete apartment block with 24 flats and about 1,900 m² of heated floor area, still served by a gas central heating system from 2004. The plant nears replacement age. The owner asks whether to switch that system to a heat-pump solution by 2027. The stakes run high. Munich pursues a city-wide heat transition that combines district-heating expansion with decentralised heat pumps ^[4][21][22]. Federal law under the Building Energy Act (GEG) steers new heating installations toward renewable shares, described in guides from Viessmann, Vaillant and the Federal Government ^[41][49][46]. For a large existing block, the choice locks in capital spending, operating costs and tenant relations for decades.

Timing sharpens the choice. The GEG 65% renewable-energy requirement for new heating systems frames any boiler replacement, as the 65% rule explainer and federal overviews outline ^[44][46][48]. Munich advances municipal heat planning that designates priority areas for district heating or decentralised solutions, a process tracked in city planning analyses ^[21][22][31]. Munich advisories map GEG deadlines and calculator tools for owners in the city ^[32][5][4]. One ADAC analysis suggests KfW trimmed heating subsidies effective 21 July 2026 ^[24]. Timing matters. An owner deciding in 2026 for implementation by 2027 must navigate overlapping legal clocks and narrowing funding windows.

Physics decides. Older concrete stock with radiators and unrenovated distribution often requires higher flow temperatures than new-build underfloor circuits tolerate efficiently ^[26][6][10]. Practitioners test suitability with the 55-degree test, which lowers flow temperatures during heating season to check comfort, a method detailed across heating guides ^[6][10][26]. Renovation sequencing shapes success, with envelope measures, hydraulics and heating surfaces preceding or accompanying heat-source replacement ^[3][15][25]. Vaillant and Viessmann document cascade and multi-family heat-pump concepts for existing stock, supplemented by industry system overviews ^[8][16][18]. Flow temperature governs efficiency and operating cost ^[26][6][10]. A 1972 block therefore raises questions about insulation, windows, radiators, hydraulic balancing and electrical capacity before sizing any heat pump.

Money governs the outcome. Heat-pump retrofits in multi-family houses require higher upfront outlay than gas boiler renewals ^[5][12][13]. Operating outlays hinge on electricity prices, gas prices and seasonal performance at given flow temperatures ^[5][26][6]. Federal funding under KfW programme 458 supports heating replacement in existing residential buildings ^[35][38][9]. Munich adds its FKG programme for climate-neutral buildings, including BEG-coupled heating-exchange modules, detailed in city guidance and Munich programme overviews ^[34][43][42]. One Reduco funding overview for Bavaria suggests combined support reached 46% federal plus 15% Munich in 2026 ^[40]. Cash shapes choices. How much net cost landlords can apportion to tenants under modernisation rules, and how operating-cost shifts affect gross rents and acceptance, will determine financial viability alongside subsidies.

Tenants feel each intervention. Heating replacement in rented stock triggers questions about apportionment, heating-bill allocation and disruption during construction. District heating offers a competing decarbonisation path in Munich districts, a trade-off examined in Munich heat-planning comparisons of district heating versus heat pumps ^[22][4][21]. High-temperature heat-pump designs promise higher supply temperatures for unrenovated radiators, an option assessed in Altbau guidance and manufacturer comparisons ^[23][1][33]. Ground-source variants involve drilling, permits and space constraints, topics covered in Buderus, Thermondo and heating-finder drilling guides ^[14][17][19]. Tenants notice disruption. The report therefore treats technical feasibility, cost and law as linked rather than isolated.

This investigation covers six linked areas. It estimates realistic retrofit costs for a heat-pump system sized for roughly 1,900 m² in a 1970s block, including heat source, distribution adjustments and ancillary construction. It reviews what the envelope needs first, from roof and facade to windows and hydraulic balancing, and how sequencing affects performance. It maps BEG support via KfW in 2026 and Munich FKG top-ups. It clarifies GEG obligations for existing large residential buildings, including renewable shares, consultation and documentation duties, and interaction with municipal heat planning. It compares electricity-driven running costs against continued gas operation. It explains tenant pass-through under modernisation apportionment. Scope stays tight. Each area draws on current German rules and Munich-specific instruments.

The report deliberately excludes several adjacent topics. It does not design a district-heating connection or compare network charges street by street. It does not engineer ground-source boreholes or assess groundwater permits for the specific plot. It omits detailed structural analysis, fire-protection redesign and indoor electrical riser calculations beyond capacity flagging. It excludes income-tax depreciation, corporate financing structures and portfolio strategy. It leaves out embodied-carbon life-cycle accounting and individual tenant behaviour modelling. Limits sharpen focus. Those exclusions keep attention on the core retrofit decision facing this building by 2027.

The report proceeds in four steps. Background sets the building baseline, the Munich policy environment and the technology palette for multi-family heat pumps. Findings present cost ranges, envelope prerequisites, subsidy mechanics, GEG duties, operating-cost drivers and apportionment rules in sequence. Discussion weighs trade-offs, sensitivities and timing risks for a 2027 implementation, including what changes if district heating arrives later or power prices diverge. Conclusion distils decision criteria and next investigative steps without pre-empting detailed design. This report follows that logic. It frames evidence for an owner decision rather than prescribing a vendor or system.

2. Background

Concrete apartment blocks erected around 1972 in Munich share a predictable fabric. Reinforced-concrete frames carry poorly insulated exterior walls, concrete balconies pierce the thermal envelope, and original roofs, cellar ceilings and single- or early double-glazed windows leak heat ^[27][29]. One renovation guide for 1950s to 1990s stock notes that this vintage typically lacks cavity insulation and airtightness detailing ^[27]. Heat escapes fast. Measured consumption in unrenovated examples often exceeds 150 kWh per square metre per year, and one Altbau insulation analysis places typical 1970s demand far above current new-build levels ^[29][27].

The existing heat source defines the next step. A gas-fired central boiler from 2004 burns natural gas in a central plant, distributes hot water through risers to radiators in 24 flats, and provides domestic hot water, often via storage tanks ^[12][5]. One heating-cost guide describes this generation as relatively compact, mature and cheap to install, with 20-25 year service lives under regular maintenance ^[12]. Evidence suggests condensing models from that era already recover flue-gas heat, but they still exhaust CO2 on site and depend on gas tariffs and chimney maintenance ^[5][12]. Replace parts now. Owners face a timing question because the boiler approaches the end of its technical life just as law tightens.

Heat pumps reverse the logic. Instead of burning fuel, they draw ambient heat from air, ground or groundwater, lift it with a compressor, and feed the same hydronic distribution at lower flow temperatures ^[16][18]. Viessmann's multi-family guide describes air-to-water units on roofs or courtyards, ground-source arrays with boreholes, and cascades that link several smaller heat pumps to cover large loads ^[16]. Vaillant documents a cascade heating a multi-family house in Bad Schwartau, where multiple units modulate together and back each other up ^[8]. Priwatt's overview of solutions for multi-family houses lists the same three families — central air-source cascades, ground-source with probes or collectors, and hybrid combinations with a second generator — and stresses hydraulic balancing, buffer storage and domestic hot-water handling ^[18].

High-temperature models narrow the gap to boilers. One comparison of Viessmann and Vaillant units for 2026 contrasts machines delivering around 70 °C versus 75 °C flow temperature with natural refrigerants ^[1]. One installer guide suggests high-temperature heat pumps suit radiators in old buildings because they sustain higher supply temperatures without electric backup ^[23]. Evidence suggests efficiency still falls as supply temperature rises, so manufacturers and planners push larger radiators, fan-assisted radiators or underfloor circuits to allow 55 °C or lower operation ^[26][23]. Physics punishes heat. Every extra kelvin of lift consumes disproportionate electricity.

Envelope work therefore precedes or accompanies a heating swap in this vintage. Effizienzhaus-online and Lenz Energieberatung both describe the accepted sequence as roof and top-floor ceiling first, then facade and windows coordinated together, then cellar ceiling and building services ^[3][25]. Evidence suggests this order cuts heating load, prevents oversized heat generators, and reduces moisture and thermal-bridge risks ^[3][28]. One sequencing guide notes that owners who replace heating before insulating often buy too much capacity and then operate the new plant part-loaded for decades ^[15][30]. Start with the shell. For a 1,900 m² concrete block, that means checking roof insulation, concrete parapets and balconies, window g-values and airtightness, and exposed heating pipes before sizing any heat pump ^[27][25].

Practitioners test suitability with the 55-degree test. Reduco's 2026 prerequisites guide and an installer explanation from HSH describe the same procedure: set the boiler curve to a maximum 55 °C flow temperature during cold weather, open all thermostatic valves, and observe whether flats stay warm ^[6][10]. Evidence suggests buildings that hold 20-21 °C room temperature at 55 °C flow need only modest radiator or hydraulic upgrades for a heat pump ^[6][10]. One heating-finder analysis ties economic operation directly to this threshold and shows annual performance factors dropping markedly above 55-60 °C ^[26]. Test first. The result calibrates radiator replacement, hydraulic balancing and the need for facade measures.

The German Heating Act, the Gebäudeenergiegesetz (GEG), sets the legal frame. The federal government describes the 2024 revision as the Act for Renewable Heating, centred on a 65% renewable-energy requirement for newly installed heating in new and existing buildings ^[46][41]. Vaillant's GEG overview and Energie-Fachberater summaries explain that the duty bites when owners install a new generator, not while an existing boiler still runs, but irreparable breakdowns trigger transition periods and advisory duties ^[49][48]. Evidence suggests municipalities with more than 100,000 inhabitants face earlier connection to municipal heat planning, which then activates the 65% rule for existing buildings ^[48][32]. One Munich GEG calculator guide links those deadlines to local gas and district-heating areas ^[32]. Law sets the frame. Fines and proof duties follow from Sections 108 and related verification rules, which the statute text and building-forum explainers detail for installation, operation and replacement records ^[47][54].

Munich adds a second clock through municipal heat planning and its Wärmewende. The City of Munich's Wärmewende pages commit to climate-neutral heat supply, expansion of district heating and geothermal sources, and phase-out of fossil individual heating ^[4]. Energy-network reporting on Munich's adopted heat plan describes far-reaching consequences for owners in designated district-heating, geothermal or hydrogen-ready zones versus areas slated for decentralised heat pumps ^[21]. One 2026 district-check guide contrasts Fernwärme connection against individual heat-pump supply street by street ^[22]. Evidence suggests owners must consult the heat plan before committing, because connection duties, subsidies and GEG fulfilment options diverge by zone ^[31][45]. Cleanthinking's national tracker notes that many large cities had to deliver plans by mid-2026, with law then linking GEG deadlines to plan publication ^[45][31]. Check the map.

Federal funding for the swap runs through Bundesförderung für effiziente Gebäude Einzelmaßnahmen, administered as KfW Programme 458 for residential buildings. KfW's product page and its current funding notices describe grants for replacing fossil heating with eligible heat pumps, including ground-source drilling and associated works ^[35][38]. The KfW programme leaflet M458 details eligible costs, technical minima and application via specialist contractors ^[9]. One multi-family calculation explainer shows how KfW caps eligible costs per dwelling unit and scales total grants with unit count, reaching up to 45,300 euros in the cited multi-family example ^[13][39]. ADAC summarises the cut effective 21 July 2026, which lowered base rates and bonuses after high demand ^[24]. KfW itself announced adjustments to BEG products and a transition phase for applications already underway ^[36]. One Bavaria funding overview translates the post-cut arithmetic into about 46% federal support in the best case ^[40]. Act early. Applications must precede contracts, and technical proof follows commissioning.

Munich layers its own Förderprogramm Klimaneutrale Gebäude (FKG) on top. The city's funding office describes an FKG module for heating replacement linked to BEG, which tops up federal grants for fuel switches ^[34]. EMA's explainer counts seven FKG modules covering heating, insulation, windows, ventilation and advice ^[43]. One specialist review of 2026 changes reports up to 60% renovation grants for multi-family houses when federal and municipal aid combine under cumulation rules ^[42]. The same Bavaria overview cited above places the Munich add-on at around 15% for heat pumps, subject to caps and budget availability ^[40]. Evidence suggests the city prioritises comprehensive retrofits and district-heating connections where the heat plan designates them, rather than isolated boiler swaps ^[4][42]. Stack funds carefully. Cumulation ceilings and EU state-aid limits cap total aid.

Running costs decide the business case after installation. Energie-Beratung Schmidt's 2026 gas-versus-heat-pump comparison frames the trade-off as lower fuel outlay for gas at purchase against higher exposure to gas commodity swings and CO2 pricing, versus higher electricity use for heat pumps moderated by seasonal performance factors ^[5]. TapTapHome's heating-cost guide lists gas boilers as cheaper to buy and service, and heat pumps as dearer to install but cheaper per unit of heat when the annual performance factor exceeds roughly three ^[12]. Evidence suggests ground-source systems achieve higher and more stable factors than air-source in cold spells, but they demand boreholes, permits and space ^[19][14]. Buderus and Thermondo drilling guides describe 50-100 metre boreholes, geological surveys, water-authority permits and spacing rules that drive cost and lead time ^[14][17]. One ground-source cost survey notes that drilling and earthworks often rival equipment costs in multi-family projects ^[2][7]. Drill once. Maintenance, chimney sweeping, gas meter fees and electricity tariff structure then shape annual bills for decades.

Tenant law governs how owners recover the investment. Modernisation-allocation guides paired with multi-family cost analyses describe the Modernisierungsumlage as the mechanism allowing landlords to apportion eligible modernisation costs to net cold rent, subject to caps, hardship objections and deduction of repair shares and public subsidies ^[5][13]. Evidence suggests only costs that permanently improve energy performance, comfort or sustainability qualify, and KfW and FKG grants must reduce the apportionable base before calculation ^[13][39]. One Munich GEG and heating-exchange guide links this rent effect to disclosure duties toward tenants before works begin ^[32]. Paperwork matters. Notices must itemise measures, cost allocation per flat, and expected energy savings, and tenants retain special termination and objection rights.

Baseline practice for a 1972 block thus combines three elements. Engineers first reduce load through roof, facade, windows and hydraulics, then size a low-temperature cascade or ground-source system validated by the 55-degree test, and owners sequence GEG compliance, heat-plan zone checks, KfW 458 applications and FKG top-ups before signing supply contracts ^[3][6][35]. High-temperature units and hybrid peaks cover residual peaks where radiators or domestic hot-water temperatures constrain design ^[1][23]. Gas remains the comparator for capital outlay and servicing simplicity, while heat pumps compete on renewable share and long-run energy cost where the envelope allows low flow temperatures ^[5][12].

3. Findings

3.1 Heat Pump Retrofit Costs for 1972 Munich MFH

Air-source cascades beat ground-source for a 1972 Munich multifamily block on upfront cost, footprint and permitting, and evidence suggests this ranking from Viessmann and Thermondo holds for dense retrofit ^[16][17]. Central cascade investment runs €40,000 to €80,000 before subsidies, according to Priwatt ^[18]. The fully loaded 20-unit air cascade lands near €125,000 including ancillary measures, and multiple sources report that total from Vaillant and Reduco ^[8][13]. The Bad Schwartau reference uses three aroTHERM plus air-to-water units at 10 kW each for 30 kW total, fixing the scale a 1970s block must replicate with buffers and backup, according to Vaillant ^[8]. Ground breaks the budget.

Per-unit air prices mislead until multiplied into a cascade. Device prices in the EnBW 24-flat comparison span roughly €5,000 for Mitsubishi to €15,000 for Viessmann per unit, with total installed cost at €11,000 to €27,000 per unit including consultancy, removal and commissioning, according to EnBW ^[11]. Heating capacity per unit spans only 7.3 kW for Stiebel Eltron to 9.7 kW for Viessmann, forcing cascade multiplication for a large block, according to EnBW ^[11]. Single-family air-to-water turnkey averages €36,000 with device €12,000-€20,000, installation €3,000-€12,000, hydraulics and storage €3,000, preparation €500-€2,500 and sound insulation €200-€800, which forces budget holders to carry more than the box, according to TaptapHome ^[12]. Small is cheap. Larger blocks scale through 2 to 5 units in parallel covering over 100 kW for 30 or more apartments, which prevents single-unit shortfall, according to Priwatt ^[18].

Gas remains cheaper to buy than any heat pump, and evidence indicates this gap from Energie-Beratung Schmidt sets the 2027 hurdle ^[5]. Air-to-water purchase including installation runs €15,000 to €42,000 by size, manufacturer and effort, while gas condensing costs only €8,000 to €15,000, leaving a €7,000-€27,000 entry premium to overcome, according to Energie-Beratung Schmidt ^[5]. One documented comparison priced a new heat pump at €30,000 against €12,000 for gas, with 30% funding deducted from the pump, which still leaves gas ahead on day one, according to HomeServe Gruppe ^[20]. A new condensing boiler alone costs €4,000 to €6,500 yet saves several hundred euros yearly, so the outlay amortises in a few years, according to effizienzhaus-online.de ^[3]. Altbau single-family installed examples run €18,000-€24,000 for aroTHERM plus and €24,000-€34,000 for Vitocal 250-A, according to Reduco ^[1]. Budget for reality. Conventional air holds JAZ 3 to 55°C then loses about 6% per extra degree to only about JAZ 2 at 70°C, raising electricity use at high flow, according to TaptapHome ^[23].

Ground-source hardware looks affordable until the borefield invoice arrives. Brine-water devices cost around €10,000 to €12,000 by design and class, which caps the box yet leaves the project open, according to Heizungsfinder ^[19]. Simple brine-water execution runs about €10,000 to €15,000 by capacity, with efficiency and extras raising price, according to Heizungsfinder ^[19]. Total sole-water including installation typically lands between €15,000 and €30,000, which already exceeds gas before drilling risk, according to waermepumpen.info ^[2]. Multiples add up fast. Installation runs about €2,500 to €3,000, according to waermepumpen.info ^[2]. Pump, storage and circuit connection adds €4,000 to €5,000 for smaller ground units and more for larger, plus roughly €1,000 for piping extras, and multiple sources report these add-ons from Heizungsfinder and waermepumpen.info ^[19][2]. Drilling of probes typically costs €6,500 to €11,000 as a major component, forcing developers to budget the ground separately, according to waermepumpen.info ^[2]. One four-unit multifamily paid €32,400 for deep drilling in rocky soil, according to nachhaltiges-zuhause.de ^[7]. Favourable shallow conditions cut the same scope to about €22,680, saving nearly €10,000 on soil alone, according to nachhaltiges-zuhause.de ^[7]. A circa 30 kW ground-source unit for four units needs €36,000 to €54,000 purchase-only, exemplified by €45,000 at Goethestrasse, which pushes MFH ground plant well above air cascades, according to nachhaltiges-zuhause.de ^[7].

Comparison of air-source and ground-source cascades for MFH retrofit.

Munich inner-city plots rarely fit the borefield a 1970s block demands, and evidence suggests this squeeze from Viessmann and nachhaltiges-zuhause.de ^[16][7]. Dense areas often restrict water or ground options for lack of space for collectors, probes or wells, according to Viessmann ^[16]. Probes save surface because drilling goes deep, while collectors need large free area problematic in dense settlement, according to nachhaltiges-zuhause.de ^[7]. Munich maps groundwater local heat, groundwater pumps, air pumps, collectors and renovation potential separately, which lets planners screen streets before drilling, according to the City of Munich ^[4]. Groundwater heating with pumps or local networks anchors the northwest and east, with collectors and air pumps supplementing, which narrows where deep probes compete, according to Energienetzwerk München ^[21]. Permits bite early. Up to 100 m needs lower water authority approval plus geological service notification, which adds weeks before mobilisation, according to Thermondo ^[17]. Beyond 100 m needs an additional mining permit from the state mining office, which adds a second authority, according to Thermondo ^[17]. Boreholes deeper than 100 m additionally need mining authority approval, according to Buderus ^[14]. Deep drilling is generally prohibited in groundwater protection zones, which can kill probes outright, according to Thermondo ^[17]. Strongly mineralized groundwater or carbon dioxide inclusions can preclude a borehole, according to Buderus ^[14]. Multiple boreholes must stay about 6 m apart and 3 m from boundaries, with about 2 m to the house, according to Thermondo ^[17]. The plot must stay accessible for heavy drilling equipment, which rules out tight courtyards, according to Thermondo ^[17]. Ancillary borehole items add €250-€600 for permits, €300-€750 for setup and €400-€500 for soil disposal, which pads per-metre rates, according to Thermondo ^[17].

Physics fixes the metres a Munich block must drill, and evidence indicates this linkage from Thermondo ^[17]. Required depth equals pump watts divided by soil extraction W per m, which turns geology into bore metres, according to Thermondo ^[17]. Mean extraction swings 30 to 70 W per m, so the same kilowatt needs double the depth in poor ground, according to Thermondo ^[17]. Gneiss, basalt, granite and sandstone deliver 35-70 W per m at the top, according to Buderus ^[14]. Limestone, clay, loam and water-bearing sand-gravel give 30-65 W per m, according to Buderus ^[14]. Dry sand-gravel falls below 20 W per m, according to Buderus ^[14]. Low yield hurts. The rule of thumb charges about €75 per bore metre and €50 per square metre of collector, which converts extra metres directly into budget, according to waermepumpen.info ^[2]. Probe drilling runs €50-€75 per metre to 100 m and around €100 per metre in harder South German rock, and multiple sources report that gradient from Heizungsfinder and Thermondo ^[19][17]. Seventy-five metres per kW (150 m for 10 kW) or 187.5 m² collector area sets the scale, forcing multi-bore fields for MFH loads, according to waermepumpen.info ^[2]. Ground extraction is 75% of heat, for example 5 kW heat needs 3.75 kW from ground, which sizes the field below headline capacity, according to waermepumpen.info ^[2]. Pricing follows local soil and chosen extraction method, which makes test drilling pay, according to waermepumpen.info ^[2]. Unknown ground that forces repeat setups to reach total metres lifts price, according to waermepumpen.info ^[2].

Efficiency favours ground, but the 1968 air reference proves air works in old stock. Fraunhofer ISE metered stock achieves mean JAZ 3.4 for air spanning 2.6-4.9 and 4.3 for ground spanning 3.6-5.4, which rewards ground with fewer kilowatt-hours per heat unit, according to Reduco reporting Fraunhofer ISE ^[13]. Across 77 buildings aged 15-170 years air averaged JAZ 3.4 with no age correlation, which puts a 1972 block in scope, according to Reduco reporting Fraunhofer ISE ^[6]. The 1968 reference runs three 10 kW aroTHERM plus units with 800-litre plus 1,000-litre buffers at 55/48°C and JAZ 4.0, which anchors realistic expectations, according to Reduco ^[13]. Two allSTOR plus buffers at 800 L and 1,000 L provide that inertia, according to Vaillant ^[8]. Plan for backup. A 63 kW ecoTEC plus gas condensing reserve backs 30 kW of pump capacity where 150 kW of gas stood before, yet the peak-load backup went unused in the first half year, and multiple sources report this bivalent outcome from Vaillant and Reduco ^[8][13]. Replacing a boiler one-for-one with same-power pump is discouraged, which forces proper load calculation, according to Viessmann ^[16]. Oversizing by factor 2 cycles constantly for COP 2.5 instead of 3.5-4.0 and adds €5,000-€10,000 over 20 years, which punishes rule-of-thumb sizing, according to Reduco ^[15]. Hydraulic balancing stays relatively inexpensive and fast, which trims flow temperature before pump day, according to HSH Installateur ^[10]. Air needs less space but averages more power, while earth and groundwater run cheaper year-round on warmer source, which explains the JAZ gap, according to Viessmann ^[16].

Running cost decides the 2027 business case more than the brochure. Opex decides. Ground-source annual electricity plus maintenance sits about €400-€500, which keeps monthly outlay low, according to waermepumpen.info ^[2]. The arithmetic is heat divided by JAZ times tariff, for example 10,000 kWh divided by 4 times €0.28 equals €700 yearly, which lets owners test bids, according to Heizungsfinder ^[19]. At JAZ 4, 2,000 hours and €0.28 plus €100 base, yearly electricity spans about €800 for 5 kW to €2,900 for 20 kW, which scales with connected load, according to Heizungsfinder ^[19]. Thirty thousand kilowatt-hours of heat at JAZ 3-4 draws about 10,000 kWh costing about €3,500 yearly at €0.35 allocated via heating bills, which sets MFH cash flow, according to Reduco ^[13]. Probes last over 50 years in the ground across unit swaps, while maintenance at about €400 yearly sustains 15-plus years, and multiple sources report this longevity from Buderus ^[14]. Rooftop PV cuts pump power cost 30-50% saving about €800-€1,200 yearly, which improves air economics most, according to ftimmobilien24 ^[22]. Electrically driven pumps count as eligible heating technology, which preserves subsidy access, according to KfW ^[9]. Munich assesses savings via demand reduction from energetic renovation, which precedes pump sizing, according to the City of Munich ^[4]. A 2027 Munich budget should carry about €125,000 gross for an air cascade with buffers and gas peak cover, less about €70,000 BEG in the documented 20-unit case, and multiple sources report those totals from Vaillant and Reduco ^[8][13].

3.2 Building Envelope and Heating Prerequisites for Heat Pumps

Envelope-first renovation cuts heating load from 16 kW to 7–8 kW, Reduco and Lenz Energieberatung document ^[15][25], allowing correct power calculation after full insulation, Bauelemente-Winter adds ^[30]. Size follows envelope, according to Bauelemente-Winter ^[30]. Windows, roof and envelope go to latest standard before heating replacement, with pre-1984 stock advised to insulate completely first, Effizienzhaus-online prescribes, evidence indicates ^[3]. New windows and improved insulation lower heating demand, so circulation pump, flow temperatures and distribution are tuned to the new lower demand, according to Effizienzhaus-online ^[3]. Insulating first permits smaller cheaper sizing and more efficient heat-pump operation in old buildings, Lenz Energieberatung notes, multiple sources report ^[25][30]. Combined heating, facade, basement, roof and window packages cut average consumption up to 70%, according to Effizienzhaus-online ^[3].

Outside-in sequencing with thermal protection first is cheapest and most reliable, Happy-Haus and Bauelemente-Winter guides concur, multiple sources report ^[28][30]. Heating modernisation and pipe insulation follow only after envelope insulation, according to Happy-Haus ^[28]. Reduco codifies six stages with envelope before technology as Stage 0 iSFP, Stage 1 roof/top ceiling, Stage 2 facade, Stage 3 cellar ceiling, Stage 4 windows/doors and Stage 5 heating plus ventilation, according to Reduco ^[15]. The iSFP compass defines optimal building-specific sequence, Reduco and Energie-Fachberater agree, multiple sources report ^[15][27]. Budget guidance flips start to windows first for greatest single losses, Oknoplast and Bauelemente-Winter note, multiple sources report ^[29][30]. Coordinate windows and facade together, according to Reduco ^[15]. Facade follows windows to fit connections in the insulation plane and avoid bridges to uninsulated walls, according to Bauelemente-Winter ^[30]. Wrong order costs 1,500–3,000 EUR rework and shifts dew point to reveals causing mold, according to Reduco ^[15]. Triple glazing in uninsulated walls moves the coldest surface to reveals with hidden condensation risk, demanding reveal insulation plus simultaneous or prior facade work or a DIN 1946-6 ventilation concept, according to Lenz Energieberatung ^[25]. Single measures without overall concept lose 10–20% effect via thermal bridges unless window joints are prepared for later facade, according to Reduco ^[15]. Recurring errors include facade-first starts, windows without wall insulation, heating before insulation causing oversizing, late funding and no overall concept, according to Lenz Energieberatung ^[25]. Single scaffolding for roof plus facade plus windows costs 6,000 EUR against 3×4,500 EUR equalling 13,500 EUR separately, saving 7,500 EUR when bundled, according to Reduco ^[15]. Distribution optimisation by hydraulic balancing is mandatory, according to ADAC ^[24], with KfW linking funding to efficiency or renewables gains plus whole-system optimisation, according to KfW ^[9].

Roof dominates losses and top-floor insulation pays back fastest, Lenz Energieberatung and Taptaphome data show, multiple sources report ^[25][23]. Uninsulated stock loses about 30% through roof, 15–20% through facade, 10–15% through windows and 5–10% through cellar floor, forcing continuous reheating, according to Lenz Energieberatung ^[25]. Roof or top-floor insulation cuts losses around 20% and window replacement about 15%, directly lowering required flow, according to Taptaphome ^[23]. Top-floor ceiling insulation saves 15–30% of heating cost equalling 375–750 EUR/yr on 2,500 EUR/yr heating, amortising in 5–10 years without funding, according to Lenz Energieberatung ^[25]. Facade insulation saves 15–25% equalling 375–625 EUR/yr, amortising in 15–25 years alone and 8–12 years with sowieso costs plus funding, according to Lenz Energieberatung ^[25]. Cellar ceiling saves 5–10% equalling 125–250 EUR/yr, amortising in 8–15 years without funding, according to Lenz Energieberatung ^[25]. Modern triple glazing reaches Uw ≤0.95 versus 2.5–5.0 for old windows, costing 500–800 EUR per PVC unit and 700–1,200 EUR per wood/alu unit or 10,000–20,000 EUR for 12–18 windows per house, according to Lenz Energieberatung ^[25]. Old double glazing to modern triple with Uw 0.76 cuts window heat loss over 70%, according to Oknoplast ^[29]. WDVS reaches 0.15–0.24 W/m²K at 130–220 EUR/m² for plaster facades, according to Reduco ^[15]. Ventilated rainscreen reaches the same 0.15–0.24 at 180–300 EUR/m² for all facades including wood, according to Reduco ^[15]. Interior insulation reaches only 0.35–0.60 at 60–150 EUR/m² but suits listed or street-facing facades where exterior work is blocked, according to Reduco ^[15]. Walkable top-floor insulation costs 50–80 EUR/m², non-walkable 30–50 EUR/m², between-rafters 80–120 EUR/m² and on-rafters 150–250 EUR/m², according to Lenz Energieberatung ^[25]. Re-cover at 100–150 EUR/m² leaves rafter insulation extra only 30–50 EUR/m² instead of 80–120 EUR/m² full cost, re-plaster at 60–80 EUR/m² leaves WDVS extra only 60–100 EUR/m² instead of 120–200 EUR/m² full, and double-to-triple upgrade adds only 40–60 EUR per window, according to Lenz Energieberatung ^[25].

Low flow temperature decides economy, not equipment brand, Heizungsfinder and HSH Installateur data show, multiple sources report ^[26][10]. Highest yearly performance sits at 30–40°C flow, Heizungsfinder reports ^[26]. Surface heating needs only 30–40°C due to very large area, according to Heizungsfinder ^[26]. Large emitting surfaces plus good insulation unlock low flow, Heizungsfinder and Taptaphome agree, multiple sources report ^[26][23]. Better walls, roof and windows cut heat loss so less output and lower flow suffice, according to Heizungsfinder ^[26]. Efficiency follows temperature lift between source and flow with floor heating at 30/35°C cutting consumption, according to HSH Installateur ^[10]. Each degree costs 2–2.5% extra, according to Heizungsfinder ^[26]. Unrenovated operation drops SPF from 4.0 to about 2.5 and raises electricity above gas cost, according to FT Immobilien ^[32]. Well-insulated operation at SPF 3–4 usually undercuts gas cost, according to FT Immobilien ^[32]. Modern 55°C flow marks the magic threshold for efficient ecological operation, according to HSH Installateur ^[10]. Up to about 55°C flow usually still heats more economically than gas or oil, according to Heizungsfinder ^[26]. Standard operation turns sharply uneconomic above about 55°C with the 55–60°C band showing steep electricity rise, according to Heizungsfinder ^[26]. Economically sensible flow sits at 50–55°C, according to Reduco ^[13]. Flow-driven JAZ decides economy and subsidy eligibility, according to Heizungsfinder ^[26]. Required flow follows energetic condition and emitter type with radiators versus underfloor, Taptaphome notes, evidence indicates ^[23]. Well-insulated buildings need only 45–55°C even with modern radiators while SCOP exceeds 5.0 at 35°C but falls to 3.5–4.0 at 60°C, according to Enter ^[33].

Basic suitability holds when flow stays below 55°C all year ideally below 50°C, according to Reduco ^[6]. Test first, then decide, according to Heizungsfinder ^[26]. Insulating roof and facade or replacing windows durably cuts demand and enables low-temperature heating, according to Heizungsfinder ^[26].

Flow-temperature suitability by insulation level and emitter type:

Radiators decide flow, hydraulics decide whether that flow suffices, Heizungsfinder and Taptaphome data show, multiple sources report ^[26][23]. Old column or ribbed radiators with tiny area often need 70–90°C and block efficient operation, according to Heizungsfinder ^[26]. Classic radiators deliver only 30–40% at 35°C, low-temperature types 50–70% and fan-assisted units 40–60% more, according to Reduco ^[6]. The low-temperature radiators need about 40–50°C, according to Heizungsfinder ^[26]. Modern panel radiators large enough often run at 50–55°C and still operate economically, according to Heizungsfinder ^[26]. Underfloor is ideal yet sufficiently large modern radiators also work efficiently at 40–55°C, according to Heizungsfinder ^[26]. Sufficiently sized radiators ran as low as surface heating in 1- to 3-family field tests with identical physics for larger buildings, according to Reduco ^[13]. Swapping only undersized units in coldest rooms for larger panel or fan models is cheapest whole-house flow reduction, Heizungsfinder and Taptaphome agree, multiple sources report ^[26][23]. The 70°C level is only reserve since balancing plus single-radiator swaps are almost always cheaper than larger plant, according to Reduco ^[13]. Sustained need above 70–75°C signals envelope failure rather than pump limits although modern propane units reach 75°C under 28 bar with one circuit, Reduco and Taptaphome note, multiple sources report ^[6][23]. Lowering demand via radiator swaps or top-floor insulation to allow standard pumps is usually more sensible, according to Taptaphome ^[23]. Balancing after roof or facade insulation is recommended, according to Effizienzhaus-online ^[3]. Without balancing near-pump radiators overheat while distant units stay cold and higher flow merely wastes energy, according to Heizungsfinder ^[26]. Balancing ensures even supply and exposes flow that only compensated maldistribution, according to Taptaphome ^[23]. Uneven test rooms reveal imbalance where balancing cuts heating cost up to 20% and is advised with any pump install, according to HSH Installateur ^[10]. Balancing may precede the first 55-degree test and is advised for efficiency at any retrofit, according to HSH Installateur ^[10]. Prior balancing improves test reliability by giving each radiator correct water volume, according to Reduco ^[6]. One multifamily example required 100-plus valves to reach 55°C flow with 48°C return, according to Vaillant ^[8]. Typical spread is 10–20 K with 40/30°C and 10 K for underfloor versus 90/70°C and 20 K for radiators, according to Heizungsfinder ^[26]. Flattest heating curve is ideal with steepness governing cold-rise and level trimming 5–15°C shoulder seasons, according to Heizungsfinder ^[26]. Curve tuning needs thermostats at maximum, below 5°C steepness steps of 0.1 with 12–24 hour waits and level fine-tuning at 5–15°C outdoors, according to Heizungsfinder ^[26]. Pre-planning needs heat-load calculation to DIN EN 12831-1 plus balancing and flow sensitivity before honest heat-pump versus hybrid versus biomass comparison, according to Metxme ^[31]. Cold rooms need calculated loads to size larger emitters for lower flow, according to Taptaphome ^[23]. The 50-degree test limits boiler to 50–55°C with all thermostats fully open for one to two days near 0°C or colder to prove warmth, according to Heizungsfinder ^[26]. The extended protocol opens thermostats to 20°C, disables night setback and observes 24–72 hours for uniform warmth, according to Reduco ^[6]. Stepwise lowering on several cold days while checking room temperatures confirms feasibility, according to Taptaphome ^[23]. Warm rooms at 55°C prove basic suitability with optional thermostat heads, hydraulic optimisation or single low-temperature swaps, according to HSH Installateur ^[10]. Cold rooms at 50°C demand single-radiator swaps before pump install, according to Heizungsfinder ^[26]. Viessmann deems 50–55°C supply worthwhile with expert checks required if higher, according to Viessmann ^[16]. Ventilation with heat recovery at 5,000–12,000 EUR planned with heating cuts demand another 10–15% and changes plant sizing, according to Reduco ^[15]. Poor insulation forces oversized plant with large buffers and full roof, window, radiator and wall renewal before sensible operation, Homeserve notes, evidence indicates ^[20][29].

3.3 Federal BEG and Munich Subsidies for MFH Heat Pumps

The 30% federal base grant decides MFH heat-pump economics in 2026, not the headline 70–80% rates ^[9]. KfW’s 458 product sheet fixes the Grundförderung at 30% of eligible total costs for all residential buildings ^[9], and the same 30% reaches landlords and WEGs explicitly, as Reduco’s MFH guide details ^[13]. The new BEG conditions apply from 21 July 2026, after KfW adjusted them in agreement with the BMWK ^[38], and KfW restarted the portal that day after freezing new filings 9–20 July 2026, according to Viessmann ^[41]. Eligible scope covers electrically driven heat pumps, solar thermal, biomass, fuel-cell and hydrogen-ready systems plus building- and heat-network connections, with planning and supervision inside eligible costs, as multiple sources report ^[35][9]. Bonuses do not save landlords, according to Reduco ^[13].

A 20-unit house commands a €215,000 eligible frame, so the full 30% lands on real costs, according to Reduco ^[13]. KfW caps eligible heating costs at €28,000 for the first dwelling, €15,000 each for the second to sixth and €8,000 each from the seventh onward ^[35][36]. Central-heating costs split equally across all units, according to Energie-Fachberater ^[39]. Reduco’s 20-unit arithmetic gives €215,000 of frame for €64,500 of base grant at 30% ^[13], while a €125,000 real investment sits fully inside and draws about €37,500, according to the same guide ^[13]. The frame shrinks fast ^[36]. Eligible costs are €27,250 from 1 February to 31 July 2027 and €26,500 to 31 January 2028, according to ADAC ^[24], and fall €750 every half-year to €22,000 from 1 August 2030, according to ADAC ^[24]. The absolute grant peaks at €22,400 at the 80% top rate ^[24][17]. Costs above the federal ceiling trigger Munich’s extra ^[34].

Self-occupancy unlocks every bonus; tenancy blocks them, according to Reduco ^[13]. KfW’s 458 sheet grants a 16% Klimageschwindigkeitsbonus for replacing old gas, oil, coal and other systems in self-occupied main residences, falling 4 points every half-year from 1 February 2027 ^[9][35]. The slide lands at 12% February–July 2027, 8% August 2027–January 2028, 4% February–July 2028 and zero from 1 August 2028, as multiple sources report ^[24][41]. The Einkommensbonus pays 40%, 30% or 10% for taxable household incomes up to €30,000, €40,000 and €50,000 on the self-used unit ^[9][36]. A €10,000 family supplement raises the threshold per household with a Kindergeld-eligible child under 18 ^[9][35]. Total federal support caps at 70%, rising to 80% at ≤€30,000 taxable income ^[35][9]. A €40,000 family with a child uses the supplement to reach €30,000 and claims €22,400 on a €32,000 pump until 31 January 2027, as KfW illustrates ^[36]. The 5% efficiency bonus and €2,500 biomass emission supplement died 21 July 2026 ^[24]. The Q1 2027 split retains 30% for EU-origin pumps and cuts non-EU toward 15%, as KfW and Viessmann describe ^[35][41]. Timing punishes delay ^[24].

Occupancy decides MFH funding compared.

BzA plus conditional contract before application decides eligibility ^[35]. KfW demands a Bestätigung zum Antrag (BzA) from a listed efficiency expert or contractor confirming technical requirements and eligible costs, including the 15-digit BzA-ID, as multiple sources report ^[35][9]. A supply or service contract with suspensive or resolutive condition on approval must already exist and show the planned completion date, with the conditional contract rule forbidding retroactive insertion ^[35][38]. The order is contract, then application via Meine KfW, then commissioning, since prior project start excludes funding, according to KfW ^[9]. One owner files the base request with implied consent, while an authorised manager files for WEG common property, as multiple sources report ^[35][13]. Bonus top-ups for self-occupied units follow within six months of base approval and before base evidence filing ^[35][9]. Proof needs tax assessments from the second and third year before application, with pension statements accepted for retirees, according to KfW ^[35]. The floor is €300 gross investment, according to KfW ^[9]. Operating, maintenance and energy-purchase costs stay ineligible, according to KfW ^[35]. Only a fossil-to-renewable switch qualifies, while replacing an existing heat pump draws no grant, according to ADAC ^[24]. Private 458 covers natural persons in the land register, while legal entities and partnerships including GbR use 459, according to KfW ^[35]. Heat pumps need JAZ ≥3.0 and ≥65% renewable coverage, as multiple sources report ^[33][24], and air-source units need 10 dB margin below statutory noise, down from 5 dB ^[6]. Drilling counts as Umfeldmaßnahme to 80% for brine-water pumps, according to Thermondo ^[17], and conversion from Etagenheizung to central, radiators and scaffolding count, according to Energie-Spezialisten ^[42]. No entitlement exists; funding depends on available federal budget ^[35][36]. File before ordering, as KfW requires ^[9].

Munich pays where Berlin stops: 15% on air-source plus 30% on the expensive ground-source excess. The City of Munich complements federal aid through its Klimaneutrale Gebäude (FKG) programme ^[37], topping electrically driven heat pumps, solar thermal and building- or district-network connections with 15% on BEG-eligible costs ^[43][40]. Ground-source and groundwater pumps earn an extra 30% only on costs above the BEG ceiling ^[34], with assessment bases capped per unit, yielding at most €9,000 on the first dwelling in one Bavarian overview ^[40]. The City’s worked example is concrete: €177,000 of costs in a ten-unit house against a €135,000 BEG ceiling leaves €42,000 excess for €12,600 of FKG extra ^[34]. Stay inside, get nothing extra, as the City states ^[34]. Eligibility is Munich-only inside postcodes 80331–81929, according to EMA Energiewelt ^[43], for buildings at least 10 years old, according to the same guide ^[43]. Owners, Erbbaurechtsnehmer, Nießbrauch holders and contractors may apply, while tenants cannot, as the City states ^[34]. An iSFP covering the measure must exist at application ^[34], confirmed later via the efficiency-measure form without filing the full plan, according to the City ^[34]. The portal message “Die beantragte(n) Maßnahme(n) dürfen beauftragt werden” releases commissioning, according to the City ^[34], and ordering the main measure beforehand still kills both main and bonus requests ^[34]. Without an expert in the federal filing, no TPN is due and the Fachunternehmererklärung suffices, according to the City ^[34]. Mixed-use houses fund only the residential share, according to EMA Energiewelt ^[43].

Stacking stops at 60% of eligible costs per measure. KfW permits cumulation with other public loans, allowances and grants to 60% of eligible costs ^[9][38], and Munich applies the same joint federal-plus-city ceiling per measure, cutting its own share when arithmetic exceeds it ^[43]. One illustration trims a 30% federal plus 20% climate plus 15% city package to 65% by cutting FKG to 10%, according to EMA Energiewelt ^[43]. The FKG base for heating disappears once any dwelling claims the federal climate-speed or income bonus, while the 30% ground-source top-up remains combinable, as multiple sources report ^[40][43]. WEGs must therefore waive those federal bonuses by resolution to keep the city base, with the manager filing, according to a Bavarian funding overview ^[40]. The safe sequence keeps both options: obtain the BEG number, then file FKG before either decision, then order, as EMA recommends iSFP → BEG → FKG → wait → order ^[43]. The KfW supplementary loan stays combinable with the grant, as multiple sources report ^[38][24], but the same costs allow only one KfW-or-BAFA application ^[9][38]. No §35c tax cumulation is allowed, according to KfW ^[9], and no BEG WG/BEG NWG combination is allowed with a three-year wait, according to KfW ^[9]. Pick one door ^[9].

3.4 GEG Obligations and Munich Heat Planning Deadlines

The 65-percent renewable mandate no longer decides Munich heating replacements. Bode and Viessmann converge on this point and multiple sources report the obligation ended with the GModG ^[44][41]. That changes the calculation. The Building Modernisation Act was promulgated on 28 July 2026 in BGBl. 2026 I No. 226 with the heating part applying since 29 July 2026 and further stages on 1 January 2027, 1 January 2028 and 1 January 2030, according to Reduco ^[15]. Owners regain free technology choice among heat pumps, heat networks, solar thermal, biomass, hybrids, gas, oil and LPG, according to Bode ^[44]. A system that must be replaced must meet the GModG requirements applicable at that time, according to Bode ^[44].

Functioning gas heating in Munich can stay in service and be repaired without triggering a swap. Bode and the Federal Government agree on this point and multiple sources report continued operation and repair remain allowed ^[44][46]. No new blanket replacement duty exists, according to Viessmann ^[41]. The hard limit is 31 December 2044 for fossil operation, after which only renewable heating is allowed, according to Viessmann ^[41]. That deadline forces a full fuel switch by 2045. Intact systems installed before 1 January 2024 may run to 31 December 2044 without mandatory replacement, according to Vaillant ^[49]. The old 30-year exchange duty is gone, according to Viessmann ^[41]. Sections §§ 71-73 GEG including that ban were repealed without replacement, according to Reduco ^[15].

New fossil boilers installed after 29 July 2026 face an escalating bio-share duty that raises fuel cost and sourcing risk, and multiple sources report Bode and Viessmann set identical stairs ^[44][41]. Bode details 10% from 2029, 15% from 2030, 30% from 2035 and 60% from 2040, according to Bode ^[44]. Meet the quota or break the law. Pure natural-gas heating became generally permitted again since 29 July 2026 but remains subject to at least 10% climate-friendly fuels from 1 January 2029 under § 43 GModG, according to Energie-Beratung Schmidt ^[5]. The quota can partly be met with solar thermal under certain conditions, according to Bode ^[44]. Fossil replacements stay unsubsidised even though the GModG re-allows them, according to ADAC ^[24].

Munich met the large-city heat-planning deadline on paper without creating owner duties. The WPG in force since January 2024 obliges every municipality to present a heat roadmap, according to CleanThinking ^[45]. Large cities over 100,000 inhabitants faced 30 June 2026 at 23:59 under § 4(1) WPG, and multiple sources report MetxMe and CleanThinking agree on that cutoff ^[31][45]. Beat the clock but not the obligation. Munich’s council passed the draft heat-planning resolution by a large majority on 22 May 2024, according to Stadt+Werk ^[37]. The city adopted the municipal heat plan on 26 November 2025 as the first decided WPG plan among Bavarian large cities with a 2035 climate-neutrality target, 90 measures, 33% district heating today and a geothermal pathway, according to MetxMe ^[31]. Its Wärmesatzung was adopted the same day, according to CleanThinking ^[45]. That statute has exclusively internal administrative effect with no external legal effect, according to the City of Munich ^[4]. The plan is an expressly non-binding orientation aid with first proposals for renewable supply, according to the City of Munich ^[4]. It imposes no obligation to install a specific system, according to the City of Munich ^[4]. Map classification alone creates no duty for an individual building with binding effect only via § 26 WPG designation, according to MetxMe ^[31].

Caption: Replacement logic for Munich gas heating under current rules | Situation | Legal requirement | Practical consequence | | Keep existing gas boiler | Up to 100% fossil operation allowed until 31 Dec 2044 ^[41] | No immediate swap required; 2045 switch must be planned ^[41] | | Install new fossil boiler after 29 July 2026 | 10% green fuels from 2029, 15% from 2030, 30% from 2035, 60% from 2040 ^[44] | Must procure biomethane or add solar thermal to stay compliant ^[44] | | Fall inside Munich heat-plan suitability area | No owner duty; map is orientation only until § 26 WPG designation ^[31] | Use GeoPortal heat map for planning, not as permit decision ^[37] |

About 290,000 Munich heating systems still burn coal, oil or natural gas with one third of all buildings on the gas network, according to Energienetzwerk München ^[21]. Munich’s mayor puts the fossil share at every second building heated with oil or gas, according to Stadt+Werk ^[37]. That stock explains the grid risk. The municipal inventory records gas and heat networks plus relevant generators and storage, according to the City of Munich ^[4]. The city orients supply through densification areas, development areas from 2025, investigation areas and decentral-supply areas, according to the City of Munich ^[4]. Heat line density per street segment serves as economic-feasibility indicator for street-laid networks, according to the City of Munich ^[4]. Munich wants most heat from underground geothermal in the long term, according to Stadt+Werk ^[37]. The plan was prepared with Stadtwerke München and external experts, according to Stadt+Werk ^[37]. Fewer users pay more. Stadtwerke München forecasts successive decline in active gas connections spreading grid costs over fewer users and raising specific grid fees, according to Energienetzwerk München ^[21].

Owner violations can cost up to 50,000 Euro while cities missing the plan face no direct fine. The penalty catalogue provides up to Euro 50,000 for offences Nos. 1-9, up to Euro 10,000 for Nos. 10-17 and up to Euro 5,000 for others, according to GEG-Info ^[51]. That scale bites. Failure to ensure § 43 GEG green-fuel generation in the required time and amount is an administrative offence under § 108 GModG, according to Gesetze im Internet ^[47]. Operating a boiler contrary to § 72(1) or (2) is an offence, according to GEG-Info ^[51]. Failing to have the § 74 inspection done correctly and on time is an offence, according to Gesetze im Internet ^[47]. No shortcut. The WPG imposes no immediate fine on municipalities missing the deadline but triggers follow-up duties and loss of legal security for construction projects, according to CleanThinking ^[45]. Concrete owner duties arise only through other laws like the GEG with their own timelines, according to CleanThinking ^[45].

Hardship, hydrogen readiness and network promises provide the only exits from fossil phase-out. The GEG foresees hardship where compliance would cause unreasonable hardship through economic overload or technical impossibility with heritage constraints, according to EWI Energy ^[48]. Exemption on application for financial difficulty, age, disability or structural circumstances remains possible, according to Energiewechsel ^[50]. Act early on exemptions. An H2-ready boiler is only allowed in formally designated hydrogen expansion areas to be fully converted by 31 December 2044 under § 71k GEG, according to MetxMe ^[31]. A contract guaranteeing heat-network connection within 10 years lets a transitional gas boiler run until connection, according to Energiewechsel ^[50]. Irreparably defective gas heating allows a used or rental interim boiler with five years to switch, or up to 13 years for gas floor heaters, according to Energiewechsel ^[50]. If network expansion or hydrogen conversion is abandoned, owners get three years to comply and a fault-based damages claim against the operator, according to Energiewechsel ^[50]. Mandatory advice before any new fossil install must cover heat-planning effects, CO2-price economics and renewable subsidies, according to EWI Energy ^[48].

3.5 Electricity Versus Gas Operating Costs and Payback

Heat pumps already undercut gas by about €749 a year at typical single-family demand despite electricity costing three times more per kilowatt-hour, according to TapTapHome ^[12]. 18,000 kWh of heat costs €1,285 with an air-to-water pump against €2,034 for gas, €1,508 for pellets and €1,710 for oil, according to TapTapHome ^[12]. The arithmetic works because one kilowatt-hour of power moves several kilowatt-hours of heat. Electricity stood at 37.0 ct/kWh against 11.93 ct/kWh for gas in a 2026 running-cost comparison, according to Reduco ^[40]. Backup heat does not erase that edge. The heating rod supplied only 1.3% of electrical work in field-tested air-to-water units, with 2024 CO2 emissions 64% below gas heating on dynamic accounting, according to Reduco ^[13]. The multiplier wins.

Running-cost comparison for electricity versus gas at stated heat demand.

Flow temperature decides whether that advantage is €500 or €900 a year. 20,000 kWh of heat needs 5,000 kWh of power at 35°C flow with seasonal performance factor 4.0 costing €1,500 a year at 30 ct/kWh, but 6,667 kWh at 55°C with factor 3.0 costing €2,000 and 8,000 kWh at 65°C with factor 2.5 costing €2,400, according to Heizungsfinder ^[26]. Lab data show what low temperature unlocks. Viessmann's Vitocal 250-A PRO on R290 with GWP 0.02 reaches 70°C flow down to -2°C outside and posts COP 5.32 at A7/W35, according to Reduco ^[13]. Field efficiency approaches that logic at good sites. 10,000 kWh of heat at seasonal factor 5.0 needs only 2,000 kWh of power costing €500-€640 a year on a 25-32 ct heat-pump tariff, while customers without that tariff pay 32-37 ct, according to Enter ^[33]. Collectors punish high lift. A four-unit horizontal collector draws 7,000-10,000 kWh a year costing €175-€250 a month because its seasonal factor runs lower, according to Nachhaltiges Zuhause ^[7]. Keep flow low.

Tariffs narrow the gap but do not erase it when seasonal performance stays above 3. All of Nachhaltiges Zuhause's operating-cost examples assume 30 ct/kWh, according to Nachhaltiges Zuhause ^[7]. Reduco's renovation case swaps 12 ct/kWh gas for about 30 ct/kWh electricity at COP 3.5 to save €1,500 a year with a 9 kW pump after complete envelope renovation, according to Reduco ^[15]. Legacy gas looked cheap. One Vaillant-documented community paid only 7.3 ct/kWh for gas while neighbours paid 15-16 ct/kWh for district heat, according to Vaillant ^[8]. That era ends on volume. Even at 10 ct/kWh, 40,000 kWh of gas still costs €4,000 a year before chimney, service and CO2 charges, according to Akkudoktor data ^[52]. Munich district heat at 10-12 ct/kWh plus €1,200-€1,500 base fee already exceeds a pump at seasonal factor 3.5 with about €2,520 electricity plus €800 for service and reserves, according to FT Immobilien ^[22]. Efficiency pays.

Maintenance favours electricity by a small but persistent margin. Gas at 11.30 ct/kWh costs €2,034 a year for 18,000 kWh plus €250-€350 for CO2 charge, chimney sweep and service, according to TapTapHome ^[12]. Earth-heat service adds about €150 a year, stated elsewhere as €150-€200, according to Heizungsfinder ^[19]. The Verbraucherzentrale puts service at €150-€300 a year per system and warns cascade contracts must clarify per-device versus per-system billing, according to Reduco ^[13]. Day-to-day running stays modest. Operating outlays run about €30-€40 a month or €400-€500 a year, according to Wärmepumpen.info ^[2]. Buderus puts annual power for a single-family earth pump at about €600-€1,000 depending on floor area, heating load and occupant count, according to Buderus ^[14]. Small sums compound.

Carbon pricing turns a narrow win into a widening gap to 2035. The national CO2 price on fossil heating rose from €45/t in 2024 to €55 in 2025, with an EU-wide trading system for building heat and transport starting in 2027, according to the Bundesregierung ^[46]. The 2026 corridor sits at €55-€65/t with no fixed price, according to Energie-Beratung Schmidt ^[5]. A multifamily block burning 12,000 cubic metres of gas a year emits about 24 t CO2, incurring about €1,440 in BEHG costs in 2026 and about €2,640 at a €110/t imputed 2030 value, split between landlord and tenant under the §5 CO2KostAufG stage model, according to MetXme ^[31]. Forward curves point higher. A planned €130/t makes gas heating roughly 50% more expensive, according to FT Immobilien ^[22]. Fossil fuels face an uncapped market CO2 price from 2028 with some experts expecting jumps to €200/t and uncertain affordable bio-gas or bio-oil supply, according to TapTapHome ^[12]. The PIK modelling cited by Energienetzwerk München sees up to €126/t by 2030 and up to €400/t by 2050, against EU ETS prints of €85.0/t in October 2023 and €64.5/t in March 2024, according to Energienetzwerk München ^[21]. Owners notice. CO2 pricing was the key lever convincing one Vaillant-documented owners' association to replace gas with heat pumps, according to Vaillant ^[8]. Delay costs.

Payback lands near a decade because upfront groundwork is heavy and yearly savings are steady. Acquisition and development costs amortise through operating savings in about a decade, according to Buderus ^[14]. Drilling alone carries a fixed setup and teardown block plus variable length, material and backfill costs, according to Wärmepumpen.info ^[2]. Total single-family development with permits, site setup and soil disposal often runs €6,000-€12,000, according to Thermondo ^[17]. Hardware adds more. Stiebel Eltron breaks single-family costs into about €20,000 for the device with entry models from €9,000 plus about €8,000 labour for around 100 hours including electrics and about €7,000 material, according to Reduco ^[13]. An optional buffer adds €1,000-€3,000 one-off, according to Buderus ^[14]. Planning costs qualify for aid. An individual renovation roadmap for the EH55 target costs €1,500-€3,500 with its own BAFA grant up to 50%, according to EMA Energiewelt ^[43]. That €1,500-a-year post-retrofit saving repays groundwork and hardware inside the ten-year window, according to Reduco ^[15].

3.6 Tenant Cost Pass-Through Under Modernisierungsumlage Rules

Subsidised heating replacements command a higher levy rate but collect less than arithmetic suggests in a 24-unit block ^[50]. The rate is 10% of apportioned heating costs per year with state subsidies and 8% without, and the Energiewechsel GEG FAQ and Viessmann guidance condition the higher rate on prior deduction of the subsidy ^[50][41]. GEG-compliant heating replacements face an additional ceiling of 0.50 euros per square metre per month within six years under § 559e, a limit the same FAQ and metxme.ai reporting impose even when the 10% calculation would allow more ^[50][31]. The cap decides the cash, according to the FAQ ^[50]. Multiple sources report the 15% maintenance deduction and the 3-euro and 2-euro six-year ceilings compared below ^[13][16].

Pass-through routes compared for heating replacement

Net math erases roughly half the headline investment before any rent increase is lawful, according to reduco.ai ^[13]. Multiple sources report that under § 559e the allocable base is total cost minus a 15% flat maintenance share deduction minus the grant before the 10% rate applies ^[13]. The subsidised share itself cannot be passed through rent, according to Federal Government guidance ^[46]. Multiple sources report the 12-unit reference of 151,000 euros eligible costs and 45,300 euros grant ^[13]. After the 15% cut 128,350 euros remain, minus the grant 83,050 euros remain allocable, or about 8,305 euros per year for the house, which at 840 square metres is about 0.82 euros per square metre per month so the 0.50-euro cap cuts collection to just over 5,000 euros per year, according to reduco.ai ^[13]. Evidence suggests KfW guidance splits the building cap equally across units, illustrated by dividing a 43,000-euro two-family total into 21,500 euros per unit ^[35][39]. Staged applications reduce the building cap by already claimed costs, according to KfW programme terms ^[9]. Doubling to 24 units halves the per-unit share, according to KfW guidance ^[35]. The cap still bites, according to reduco.ai ^[13].

Unsubsidised projects keep the 8% label but face tighter six-year ceilings ^[18][16]. The general rate is 8% of costs after deduction of funding on annual rent, a rule Priwatt and the ftimmobilien24 summary state identically ^[18][32]. Multiple sources report that a 30,000-euro net share at 8% is 2,400 euros per year or 200 euros per month, while an 8-family 30,000-euro own share is 300 euros per dwelling per year ^[16][18]. Small flats never collect the arithmetic, according to Viessmann ^[16]. Evidence suggests the six-year rent ceiling is 3 euros per square metre, or 2 euros where rent sits below 7 euros per square metre ^[16][13]. Choosing no funding despite eligibility drops the project into general § 559 at 8% per year, yet the 0.50-euro heating limit under § 559 para 3a sentence 3 still applies alongside the 3-euro or 2-euro overall ceilings, according to reduco.ai ^[13]. Heating-cost savings count too, with two-thirds deducted from the base, according to the ftimmobilien24 summary ^[32]. Missing the mandatory consultation under § 71m halves the allocable costs to 50% under § 71o, according to metxme.ai ^[31].

Hardship stops the 65% renewable duty before rent law even starts, according to dabonline ^[53]. Evidence suggests dabonline and ftimmobilien24 summaries list unreasonable personal circumstances, investment disproportionate to building value or to income, at least six months of continuous income-dependent benefits, age 80-plus self-use and monument protection as hardship or exemption grounds ^[53][32]. Landlords must announce the modernisation three months before construction starts, according to ftimmobilien24 ^[32]. For 24 letters that notice must translate the house net into per-dwelling euros per month after the 0.50-euro test, evidence suggests ^[50][31]. Paperwork decides enforceability, according to ftimmobilien24 ^[32].

Operating-cost law decides whether tenants feel the heat pump as relief, according to Gebäudeforum ^[54]. § 71o reserves operating-cost distribution to ordinance under § 6 authorisation, according to Gebäudeforum ^[54]. At JAZ 3.4 and 40.55 cents per kWh, usable heat costs about 11.9 cents per kWh, according to Energie-Beratung Schmidt ^[5]. Evidence suggests that level leaves only partial savings to offset the levy because two-thirds of savings already reduce the base ^[5][32]. A dedicated heat-pump tariff or grid-fee discount for controllable loads pushes the price lower, with a four-figure effect on a central meter for the whole house, according to reduco.ai ^[13]. Passing conversion investment into annual heating costs of low-income tenants drives housing flight, according to the Munich energy network ^[21]. Bills move votes, according to the network ^[21].

4. Discussion

Postponing a full-size cascade on an untouched 1972 envelope avoids locking in oversize. Reduco puts central air cascades at €40,000 to €80,000 before aid, rising near €125,000 fully loaded with buffers, controls and gas peak cover for a 20-unit house ^[13], while Vaillant's Bad Schwartau project demonstrates three parallel air-to-water units serving a multifamily block ^[8]. Ground-source competes on seasonal performance, with Viessmann and Heizungsfinder pointing to mean factors around 4.3 for ground against 3.4 for air ^[16][26], but Buderus and Wärmepumpen.info price probe drilling at €6,500 to €11,000 or €50 to €75 per metre to 100 m, near €100 in hard rock ^[2][14], plus 6 m hole spacing, boundary clearances, heavy access and water-authority permits with bans in protection zones ^[14][17]. Envelope work shrinks the plant instead. Effizienzhaus-online describes roof-first, then facade, cellar ceiling and windows cutting load from about 16 kW to 7-8 kW ^[3]. Prove low flow first. Reduco and HSH-Installateur prescribe multi-day tests with thermostats open to confirm operation at or below 55°C ^[6][10]. (see 3.1)

Chasing headline grant rates misreads 2026 arithmetic. KfW product 458 grants 30% of eligible heating costs to all residential holders including landlords under terms effective 21 July 2026 ^[9][35], and Energie-Fachberater calculates a 20-unit frame at €215,000 for €64,500 base aid, fully covering a €125,000 job for about €37,500 ^[39][35]. Evidence suggests Munich's FKG adds 15% on BEG-eligible costs for electrically driven pumps, solar thermal and network links ^[34][40], with an extra 30% only on costs above the federal ceiling for ground-source and groundwater systems ^[34][43]. Cumulation caps at 60% of eligible costs, with the city trimming its share beyond ^[34][43]. ADAC notes self-occupied climate-speed and income bonuses stay closed to rented investor units ^[24]. Should owners rush before frames slide toward €22,000 from August 2030 ^[39]? No. The 30% base plus 15% city stack persists within budget, while envelope-first spending preserves eligibility for planning, conversion and ancillary work ^[9][34]. Wait and prepare. (see 3.3)

Legal pressure no longer forces a 2027 swap. The Bundesregierung heating law page and Viessmann's GEG explainer record repeal of the 65% renewable duty through the Building Modernisation Act, applied from late July 2026 ^[46][41]. Evidence shows functioning gas plant may continue and undergo repair until fossil operation ends 31 December 2044 ^[46][41], while newly fitted fossil boilers stay allowed but lose subsidy and face rising green-fuel shares from 2029 through 2040 ^[41][50]. Munich's heat plan, adopted November 2025 with climate-neutrality and geothermal aims, acts as orientation aid; Stadt+Werk and the city's Wärmewende page assign it no individual installation duty ^[37][4]. Breaches still risk fines to €50,000 ^[47][51]. Does local mapping override federal freedom? No. Energienetzwerk-MUC and FT-Immobilien describe Munich classifications as non-binding signals amid a large fossil stock and likely higher specific grid fees as connections fall ^[21][22]. Law grants time. (see 3.4)

Running-cost math rewards low flow and punishes high flow. Energie-Beratung Schmidt compares 18,000 kWh heat at €1,285 with air-to-water against €2,034 for gas, €1,508 for pellets and €1,710 for oil ^[5][12], a gap one dataset attributes to each kilowatt-hour of power moving several of heat with backup covering only 1.3% of electrical work and emissions 64% below gas ^[5]. Evidence links savings tightly to flow: 20,000 kWh heat needs 5,000 kWh power at 35°C with factor 4.0 costing €1,500 yearly at 30 ct/kWh, but 6,667 kWh at 55°C with factor 3.0 costing €2,000 and 8,000 kWh at 65°C with factor 2.5 costing €2,400 ^[5][26]. Heizungsfinder anchors economical operation at or below roughly 50-55°C, with about 2-2.5% extra use per added degree ^[26]. Can a high-temperature pump rescue an unrenovated block? Taptaphome reviews 70°C units for old stock ^[23], yet field factors slide from around 3 at 55°C toward 2 at 70°C ^[26][23]. Temperature rules. (see 3.5)

Rent law converts technical efficiency into landlord cash flow, but caps blunt headline percentages. FT-Immobilien München and EWI Energy describe subsidised heating replacement allowing 10% yearly on apportioned heating costs against 8% unsubsidised, after deducting 15% maintenance share and then the grant ^[32][48], while the general route deducts funding and two-thirds of heating-cost savings ^[32][48]. Evidence caps collectable heating uplift at €0.50 per square metre monthly within six years, alongside €3.00 general ceilings or €2.00 where rent sits below €7.00 ^[32][48]. Energie-Fachberater and FT-Immobilien illustrate the bite: €151,000 eligible costs fall to €128,350 after maintenance and to €83,050 allocable after a €45,300 grant, about €8,305 yearly, which at 840 m² equals €0.82 monthly and drops under the cap to just over €5,000 yearly ^[39][32]. Missed mandatory consultation halves allocable costs, and landlords must announce work three months ahead with per-dwelling amounts after the cap test ^[32][48]. Caps bite. Hardship rules can block duty on disproportionate investment, long-term benefit receipt, age 80-plus self-use or monument status ^[41][48]. (see 3.6)

Consider the strongest case for immediate 2027 electrification at full strength. It runs like this: lock the 30% federal base plus 15% Munich aid before half-yearly frames sink and budgets exhaust, escape the carbon-price climb from €45 per tonne in 2024 toward a €55-€65 corridor in 2026 and an EU-wide heat-and-transport system from 2027 with higher forwards, dodge rising specific grid fees as Munich gas connections dwindle, avoid paying twice for scaffolding, outages and a 23-year-old 2004 boiler that could fail, and copy the 1968 house that hit factor 4.0 at 55/48°C with 800- and 1,000-litre buffers where a 63 kW gas reserve stayed idle for half a year ^[5][21][8]. That case deserves weight. High flow destroys it. Heating an unrenovated 1972 block at 65-70°C drags air-source factors toward 2.0-2.5 and lifts power draw from 5,000 kWh to 8,000 kWh for the same heat, erasing the €749 yearly edge Schmidt quantifies ^[5][26]. Reduco's 55-degree test and hydraulic balancing plus selective radiator swaps prove lower flow for a fraction of plant cost ^[6][10], while KfW's base aid and Munich's top-up combine to 60% and cover planning and conversion work when sequenced correctly ^[9][34]. Vendor comparisons touting 70-75°C operation ^[1] lose to field performance data from Heizungsfinder on this point. Immediate swap still wins on one dimension. Delay prolongs exposure to gas and carbon volatility through 2027-2030. Concede that risk. (see 3.2)

Two variables dominate all others. Achievable flow temperature fixes the power bill, and net allocable rent after maintenance deduction, grant subtraction and the €0.50 ceiling fixes payback. Evidence gaps qualify confidence. No room-by-room load calculation, blower-door result or Munich boring log pins down this house's 100 kW-plus need or soil extraction at 30-70 W per metre ^[14][17]; Nachhaltiges Zuhause suggests four-probe rocky drilling at €32,400 against €22,680 in easy ground ^[7]. FKG budget exhaustion, half-yearly BEG frame cuts, forward power and gas tariffs, forthcoming EU carbon values and PV-roof yield defy firm forecasting ^[24][38][40]. Single-family payback near a decade does not transfer cleanly to a 24-flat block ^[5][12]. Weighing those limits, postpone the complete gas-to-pump changeover past 2027. Renovate roof, facade, glazing, basement ceiling and hydronics first, validate operation at or below 55°C, then fit an air-to-water cascade around €125,000 retaining the boiler for peaks while stacking the 30% federal grant with the 15% Munich supplement. The amended law lets the 2004 unit run to 2044, cheaper heat-per-kilowatt-hour accrues only after flow falls, and capped apportionment rewards load reduction before electrification. Act in sequence. (see 3.3)

5. Conclusion

Keep the 2004 gas boiler running, slash load and flow temperature through fabric and hydraulics, then electrify with a bivalent air cascade drawing federal and Munich aid ^[41][8][34].

One report suggests sequencing roof or top-floor ceiling first, then facade, cellar ceiling, windows with facade, then heating and ventilation, with shared scaffolding trimming cost ^[3]. Evidence suggests combined packages cut use by up to 70% and lower design load from around 16 kW toward 7-8 kW, which shrinks pump size and auxiliary power ^[3][25]. Start with the roof. Evidence suggests Heizungsfinder, Reduco and installer practice quantify about 2-2.5% extra consumption per extra degree, with sweet spot at 30-40°C and economic operation at or below 50-55°C ^[26][6][10]. One report suggests Oknoplast seats windows in the insulation plane with facade work to avoid bridges, dew-point shift, condensation and rework ^[29]. Evidence suggests heat-load calculation, balancing, flat-curve tuning and multi-day 55-degree tests with thermostats open validate low-temperature readiness ^[6][10]. Prove 55°C first.

Air cascades fit this block better than probes. Vaillant's Bad Schwartau write-up, Viessmann MFH guidance and Reduco costing frame a fully loaded 20-unit air system near EUR 125,000 with buffers, ancillaries and gas peak cover ^[8][16][13]. Evidence suggests core cascade outlay runs EUR 40,000-80,000 before aid, for example three 10 kW air-to-water units giving 30 kW, while single catalogue units deliver only 7.3-9.7 kW so larger blocks parallel 2-5 machines past 100 kW ^[13][11]. Evidence suggests gas condensing at EUR 8,000-15,000 against air-to-water at EUR 15,000-42,000 and EUR 36,000 single-family turnkey ^[12][5]. Vendor sheets decisively settle low-temperature cascade feasibility: the 1968 reference ran 55/48°C at seasonal factor 4.0 on 800-litre plus 1,000-litre buffers with a 63 kW gas reserve behind 30 kW of pumps unused for half a year ^[8]. Buderus, Thermondo, waermepumpen.info and Heizungsfinder detail drilling at typically EUR 6,500-11,000 or EUR 50-75 per metre to 100 m, near EUR 100 in hard rock, plus 6 m spacing, boundary setbacks, rig access and water-authority bans, outweighing the mean factor edge of 4.3 over 3.4 for air as air slides from around 3.0 at 55°C toward 2.0 at 70°C ^[14][17][2]. Skip drilling.

KfW product 458 anchors 2026 funding. KfW paperwork, KfW online guidance and ADAC summaries place new BEG terms from 21 July 2026 after freeze and restart, with 30% base for all residential owners including landlords and central plant split equally ^[9][35][24]. Energie-Fachberater, KfW arithmetic and Reduco MFH costing set the 20-unit frame at EUR 215,000 for EUR 64,500 base, covering a EUR 125,000 job for about EUR 37,500, stepping down toward EUR 22,000 from August 2030 ^[39][9][13]. One report suggests rented investor flats cannot add speed, income or efficiency bonuses that ended 21 July 2026 ^[40]. The City of Munich FKG, Energie-Spezialisten and ema-energiewelt add 15% on BEG-eligible electric-pump costs plus 30% only above the federal ceiling for ground-source, for Munich postcodes, buildings over 10 years, iSFP at application and no early order ^[34][42][43]. Evidence suggests cumulation caps at 60% with Munich trimming excess, and any flat claiming federal speed or income bonus forfeits city heating base while ground top-up stays combinable, forcing WEGs to waive those bonuses and file contract-then-application via Meine KfW with BzA ^[34][40]. File in order.

Reformed law lets the boiler stay. The federal government, Viessmann law guidance and energy advisers confirm the Modernisation Act from late July 2026 scraps the 65% duty, restores technology freedom and allows repair and operation of working gas heat until 31 December 2044 ^[46][41][48]. Evidence suggests new fossil installs stay allowed but unsubsidised with rising green-fuel shares 2029-2040, fines to EUR 50,000 and narrow hardship, hydrogen-area and interim-boiler exceptions after mandatory advice ^[41][47]. Stadt+Werk, Munich network analyses and city heat documents describe the November 2025 heat plan as orientation aid without individual swap duties, while shrinking gas connections lift specific grid fees ^[37][21][4]. Wait lawfully.

One report suggests Energie-Beratung Schmidt meters 18,000 kWh heat at EUR 1,285 air-to-water versus EUR 2,034 gas, EUR 1,508 pellets and EUR 1,710 oil, despite threefold power price, because one power unit moves several heat units with 1.3% backup share and 64% lower emissions ^[5]. Evidence suggests 20,000 kWh heat needs 5,000 kWh at factor 4.0 and 35°C for EUR 1,500 yearly at 30 ct/kWh, but 6,667 kWh at factor 3.0 and 55°C for EUR 2,000 and 8,000 kWh at factor 2.5 and 65°C for EUR 2,400 ^[5][26]. One report suggests dedicated pump tariffs and controllable-load discounts preserve the edge above factor 3 ^[5]. One report suggests carbon pricing climbed from EUR 45/t in 2024 to EUR 55 in 2025 inside EUR 55-65 in 2026, with EU-wide building-transport pricing from 2027 widening the gap toward decade amortisation ^[5]. Hold 55°C.

Evidence suggests subsidised heating swaps levy 10% yearly on apportioned heating share versus 8% unsubsidised, after 15% maintenance cut and grant deduction, capped at EUR 0.50 per square metre monthly within six years ^[39][41]. Evidence suggests the cap binds first: EUR 151,000 eligible falls to EUR 128,350 then EUR 83,050 allocable after EUR 45,300 aid, or EUR 8,305 yearly, equalling EUR 0.82 at 840 m² and cut to just over EUR 5,000, split equally and roughly halved per flat toward 24 units ^[39][50]. One report suggests the general path deducts aid and two-thirds savings under EUR 3.00, or EUR 2.00 below EUR 7.00 rent, yet the EUR 0.50 heating ceiling still bites even if aid is declined ^[50]. Evidence suggests landlords must give three months notice with per-flat uplift after the cap test, while hardship pauses, still needing the listed expert's BzA split for the exact 24-flat allocation, cover disproportionate cost, long benefit receipt, age 80-plus self-use or monument cover ^[32][47]. Size for the cap.

Confidence splits by risk. Fabric-first sequencing carries high confidence; only a failed 55°C test after full retrofit flips it toward high-temperature pumps or hybrid retention ^[6][10]. The EUR 125,000 bivalent budget carries medium confidence; a structural roof overrun or split scaffolding flips timing ^[13][8]. Subsidy stacking carries medium confidence; a mid-year BEG frame cut or FKG pause flips net cost ^[35][34]. Operating advantage carries medium confidence; a power-tariff shock without pump tariff or a carbon freeze flips payback ^[5]. Lawful waiting carries high confidence; only a network connection order flips it ^[41][37]. Watch tariffs.

Immediate swap locks 30% base before frames slide toward EUR 22,000, dodges carbon and grid-fee climb as gas connections thin, banks around EUR 749 yearly saving at once and avoids remobilising scaffolding ^[24][5][13]. That case wins if the boiler fails beyond repair, the block already logs 55°C, Munich signals FKG tightening, or carbon forwards jump ^[41][6][34]. Otherwise delay pays.

Prove 55°C this winter. Evidence suggests the cascade then meters near factor 3.0 at 30 ct power, holding power-per-heat below gas ^[5][26]. Insulated Munich blocks will heat below gas cost in 2030 while early full swaps still pay high-flow penalties ^[5][26].

References

^[1] Viessmann oder Vaillant Wärmepumpe 2026: Vergleich, 70 vs 75 °C — https://reduco.ai/blog/heizung/viessmann-oder-vaillant-waermepumpe · general ^[2] Was kostet eine Erdwärmepumpe? — https://www.waermepumpen.info/erdwaermepumpe/kosten · general ^[3] Die richtige Reihenfolge bei der Sanierung ist wichtig — https://www.effizienzhaus-online.de/daemmung-oder-heizung/ (deu) · government ^[4] Wärmewende für München — https://stadt.muenchen.de/infos/waermewende-muenchen.html · government ^[5] Wärmepumpe oder Gasheizung 2026? 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Source quality: 10 government, 10 professional, 34 general.