Heat pump in an older German home 2026: cost, funding, running costs

Updated: 2026-07-12 · Reading time: 11 min · ImmoLens editorial team

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This guide was written by the ImmoLens editorial team and last reviewed on 2026-07-12. The information is for orientation and does not replace legal, tax or financial advice.

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With the Gebäudeenergiegesetz 2024 (GEG, the German buildings energy act), the question of "the cost of a Wärmepumpe (heat pump) in an older building"is no longer an academic one for property buyers. If you buy an existing building with oil or gas heating, you have to switch to renewable energy when the heating system is replaced, and in many cases that means a heat pump. This guide shows realistic investment costs, which funding pots apply in 2026 and when a heat pump makes economic sense in an older building.

ℹ️ An air-to-water heat pump in an older building costs €30,000-55,000 gross in 2026 (unit plus installation plus hydraulics). After KfW 458 funding (BEG), a share of €18,000-38,000 of your own money is usually realistic, depending on the condition of the building and the funding rate.

1. When does a heat pump make sense in an older building at all?

The decisive technical figure is the flow temperature (Vorlauftemperatur): the lower the temperature the heating system can work at, the more efficiently the heat pump runs (measured as the JAZ, the Jahresarbeitszahl or seasonal performance factor). Modern renovations of older buildings often allow flow temperatures below 55 °C:

Building condition	Typical flow temperature	Heat pump suitability	Expected JAZ
Well insulated (KfW 85 or better)	35-45 °C	✅ Very well suited	3.8-4.5
Partly renovated (roof/windows renewed)	45-55 °C	⚠️ Suited with limitations	2.8-3.5
Unrenovated (built before 1980)	60-70 °C	❌ Uneconomical without renovation	1.8-2.4

⚠️ Caution: A JAZ below 2.5 means the heat pump consumes more than a comparable gas heating system, and at higher electricity prices. A heat pump without renovating the building is not an economical solution in many older buildings. So always look at the two together.

2. Investment costs 2026: three scenarios

Scenario	Gross cost	Funding (KfW 458)	Your own share
Well-insulated detached house (EFH), air heat pump	€28,000-38,000	approx. €10,500-15,000	€17,500-25,000
Older detached house (EFH) plus hydraulics plus radiators	€40,000-55,000	approx. €15,000-20,000	€25,000-38,000
Apartment building (MFH) / ground-source variant (EWP)	€55,000-90,000	up to approx. €30,000	€30,000-65,000

3. What the investment costs: the 6 main items

🌡️

Heat pump unit (air/water)Unit including outdoor and indoor unit: €10,000-20,000. Ground-source systems (brine/water) are more powerful but more expensive: €15,000-28,000 for the system alone.

🛢️

Buffer tank and domestic hot waterHydraulic buffer tank (200-500 l) and hot water cylinder: €2,000-5,000. With a combined tank solution this is often cheaper to bundle.

🔩

Hydraulic balancing and pipeworkMandatory for a funding application (BEG), and sensible anyway: €1,500-4,000. Without hydraulic balancing the heat pump runs inefficiently.

♨️

Replacing radiators or installing underfloor heatingAt high flow temperatures (> 55 °C), switching to larger low-temperature radiators or underfloor heating is often necessary: €3,000-12,000 depending on the area.

⚡

Electrical connection and meterStronger fusing (usually 3-phase, 16-25 A), a heat pump tariff meter, and possibly groundwork: €1,000-3,500.

🏗️

Ancillary work (drilling, foundation, refrigerant lines)For ground-source: a 100-150 m deep borehole costs an extra €8,000-15,000. Foundation slab and sound insulation measures for the outdoor unit: €500-2,000.

4. Funding in 2026 at a glance

Programme	Type of funding	Base funding rate	Max. funding rate	Funding cap
KfW 458 / BEG Einzelmaßnahme (single measure, BAFA)	Grant	30% (heating replacement)	70% (incl. climate bonus plus income bonus)	€30,000 in eligible costs (first residential unit in a detached house), so a grant of max. €21,000
KfW 358 / KfW 359 (energy-efficient renovation)	Loan (low-interest)	from 2.37% effective annual interest	Up to KfW Effizienzhaus 55	€150,000 per residential unit
Bundesförderung Effizienzgebäude (BEG WG, federal funding for efficient buildings)	Loan plus repayment grant	5-20% depending on the EH level	Up to EH 40 Renewable Ready	€150,000 per residential unit

💡 Tip: As a buyer, you should mention the speed bonus of 20% (only until 31.12.2028, for working oil or gas heating systems that are ≥ 20 years old) in the purchase talks: it raises the total funding rate from the 30% base rate to up to 70%. Important when you do your own maths: the 70% do not apply to the invoice total, they apply to the eligible costs, and those are capped at €30,000 for the first residential unit in a detached house. The grant is therefore at most €21,000, even if the system costs €40,000.

5. Running costs: heat pump vs. gas

Heating system	Energy price (2026)	Annual consumption (150 m² detached house)	Annual cost (heating)
Gas heating (η = 97%)	~12 ct/kWh	~18,000 kWh gas	~€2,160
Heat pump (JAZ 3.2)	~28 ct/kWh electricity (heat pump tariff)	~5,600 kWh electricity	~€1,570
Heat pump (JAZ 4.0) plus PV	~15 ct/kWh (self-consumption)	~4,500 kWh electricity	~€675

6. The typical process when buying a house and retrofitting a heat pump

Buyer roadmap: planning a heat pump in an older building

Check the Energieausweis→Determine the flow temp.→Energieberater (BAFA-certified)→Submit the funding application (before the order!)→Installation and acceptance

The funding application must be submitted before the contract is awarded, otherwise the funding is forfeited

7. Frequently asked questions about heat pumps in older buildings (FAQ)

Does a heat pump work without a full renovation first?

Yes, if the flow temperature stays below 55 °C. That is also possible in older buildings if the roof, windows and basement ceiling are already insulated. A complete core renovation is not a mandatory prerequisite, but better insulation improves the JAZ and reduces electricity consumption considerably.

What does a heat pump really cost once everything is included?

Realistically €35,000 - 50,000 for a typical older detached house, once the hydraulics, radiator replacement and electrical work are included. After funding (KfW 458 with the base funding rate of 30%), an average of €24,000-35,000 remains as your own share.

What is the JAZ and why does it matter so much?

The Jahresarbeitszahl (JAZ, seasonal performance factor) states how much heat energy the pump produces per kWh of electricity used. A JAZ of 3.5 means: 1 kWh of electricity becomes 3.5 kWh of heat. Below a JAZ of 2.5, a heat pump in an older building is usually less economical than a modern gas heating system, and that is a decisive point in the purchase decision.

When is a heat pump not worth it in an older building?

If the building is unrenovated and needs flow temperatures above 60 °C, if there is no space for an outdoor unit or a deep borehole, or if the renovation costs (radiators, hydraulics, insulation) together prevent an economical payback within 15 years. In such cases a hybrid solution (heat pump plus a gas peak-load boiler) can make sense.

Which documents do I need for the funding application?

The Energieausweis, a specialist planner's confirmation (from a BAFA-certified Energieberater), a cost estimate from the installation company and proof of ownership. Important: the application must be submitted before the contract is awarded to the company carrying out the work, otherwise the funding lapses.

Am I obliged to replace the heating system after buying the house?

Under the GEG 2024 there is generally a transition period of up to 2 years when ownership changes. After that, the GEG requirements apply depending on the building and the type of heating (65% renewable energy when a new heating system is installed). Existing heating systems that still work may continue to be operated until they break down.

💡 Tip: Plan the heat pump and the bathroom renovation together if you can: both measures tie up the same trades (plumbing, electrics), and combined jobs are often quoted more cheaply. Funding can be applied for separately for each measure.

8. Further guides

Analyse heating and energy data from the listing

ImmoLens reads Energieausweis data and heating details from listings and lays out renovation needs and funding potential in a structured way for your purchase decision.

Analyse the listing

The next step for your property

Check your listing for free with AI: renovation costs, funding programmes and risks in a few minutes. Start your analysis, or use the free tools: Closing cost calculator, Budget calculator, Viewing checklist.