Heat pump in old buildings: Requirements, costs, subsidies and best solutions 2025
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Stefano Fonseca ist Ingenieur für Energie und Umwelt mit über sechs Jahren Erfahrung in der technischen Gebäudeausrüstung (TGA). Er kombiniert technisches Fachwissen mit einer Leidenschaft für verständliche Kommunikation. Seit mehr als fünf Jahren schreibt er als freiberuflicher Redakteur über erneuerbare Energien und nachhaltiges Wohnen, insbesondere über Photovoltaik und Wärmepumpen.
Many old buildings are considered unsuitable for heat pumps — but is that really true? Modern technology, targeted renovation and clever combinations often make the switch possible. In this article, you will find out when a heat pump in an old building pays off, which requirements must be met and how high the costs actually are.
When does a heat pump make sense in an old building?
A heat pump is useful in old buildings if the building is well insulated and can be heated with low flow temperatures. Old buildings with already renovated outer walls, modern windows and large radiators or floor heating are particularly suitable. The heat pump can then work efficiently and avoid high operating costs.
Requirements for a heat pump in an old building
For a heat pump in an old building to work efficiently, the building must meet certain requirements. Good insulation of the façade, roof and windows as well as low heat consumption are crucial. The heating surfaces must be as large as possible and be able to work with low flow temperatures, for example via underfloor heating or suitable low-temperature radiators. In addition, there must be sufficient space for the heat pump and, if applicable, a hot water or buffer tank. A suitable power connection and professional planning, including heating load calculation, are also necessary.
The following is a checklist to help you find out whether your old building is ready for a heat pump.
This checklist helps with the initial assessment. For a detailed assessment, you should consult a specialist company or energy consultant.
Does a heat pump make sense in unrenovated old buildings?
In unrenovated old buildings, the use of a heat pump is usually not useful, as the high heat demand and lack of insulation lead to inefficient operation and high electricity costs. Only through renovation measures such as new windows, façade insulation or modern radiators can a heat pump work economically.
Which heat pump is the best for old buildings?
The best heat pump for old buildings is an air-water heat pump. It is the least expensive, easy to install and provides numerous installation options. It is important that the building meets the requirements for efficient operation. If the heat requirement is very high, a hybrid heating be useful.
Here is a comparison of different types of heat pumps for old buildings:
Can a heat pump also work without underfloor heating?
A heat pump can also function without underfloor heating if sufficiently large radiators are available that work with low flow temperatures. Alternatively, special low-temperature radiators can be used. It is crucial that the heating system operates efficiently at a maximum of 55 °C.
Which radiators are suitable?
Low-temperature radiators with a large surface area and fan support are suitable for heat pumps in old buildings. These include panel heaters, special heat pump radiators and fan coil units. They emit enough heat even at low flow temperatures and ensure efficient operation. Classic cast iron or sectional radiators are usually unsuitable because they require high temperatures.
Costs of a heat pump in an old building
Depending on the condition of the building and technology, a heat pump in an old building costs between 25,000 and 45,000 euros. This sum includes not only the heat pump itself, but also installation, dismantling of the old heating system, possible insulation measures and adjustments to the heating system such as new radiators or hydraulic balancing.
The following is an overview of costs:
The operating costs of a heat pump in an old building depend on the energy requirements of the house, the efficiency of the system and the current electricity price. In a well-renovated single-family house, electricity consumption is between 4,000 and 8,000 kWh per year, depending on the type of heat pump. This corresponds to around 1,200 to 2,400 euros of electricity costs per year (at 30 ct/kWh) — i.e. 100 to 200 euros per month.
Funding options for heat pumps in old buildings
Heat pumps in old buildings are financed by subsidies and low-interest loans as part of the Federal Funding for Efficient Buildings (BEG) promoted. When replacing an old heating system, owners can apply for the KfW subsidy 458 or, in addition, the supplementary loan 358/359.
The KfW subsidy 458 covers up to 70% of eligible costs. For single-family homes in old buildings, investment costs of up to 30,000 euros are taken into account, which corresponds to a subsidy of up to 21,000 euros. A prerequisite is the installation of a climate-friendly heat pump (e.g. with natural refrigerant).
In addition, the KfW loan 358/359 can be used: It allows an effective annual interest rate of 0.01% for loans of up to 120,000 euros per residential unit. Householders with an annual income of up to 90,000 euros benefit from particularly favourable conditions.
This funding applies specifically to existing buildings — including old buildings — and makes the switch to a heat pump more economically attractive.
Is a heat pump worthwhile in an old building?
A heat pump is worthwhile in an old building if the building is well insulated and can be heated with low flow temperatures. It saves energy costs in the long term, reduces CO₂ emissions and receives government funding. Especially when gas prices rise, the heat pump is a future-proof solution.
The following example looks at a typical single-family house in an old building with an annual heat requirement of 18,000 kWh. The annual operating costs of an air-water heat pump are compared with those of a gas heating system, based on average energy prices in 2025.
In this example, funding reduces costs by 55%. 550 euros are saved annually in operating costs and after 20 years, the total savings amount to 6,400 euros. The heat pump in the old building pays off after around 8 years.
Experience with heat pumps in old buildings
A user reports in Home Technology Dialogue Forumthat his heat pump also works well in an old building without underfloor heating because it has achieved an annual performance factor (JAZ) of around 3.5 — this shows that with correct hydraulics and good planning, a heat pump in an old building can work efficiently.
In Battery Doctor Forum Does a user share an experience report of a self-installed heat pump. Although efficiency is limited, the effort is worthwhile. The heat pump had proven itself in old buildings, reduced heating costs and remained reliable despite simple self-installation.
In Finanztip forum A user warns of the risks: His modernized old building consumed almost 14,000 kWh of electricity in one year, resulting in electricity costs of around 7,000 euros — which was around twice as expensive as before with gas heating.
These three experiences show that heat pumps can work in old buildings — but only with good planning, installation and regular maintenance. Otherwise, there is a risk of high electricity costs, as the negative experience report impressively shows.
When is hybrid heating worthwhile in an old building?
Hybrid heating is worthwhile in old buildings when the heat demand is high and a heat pump alone would not work efficiently enough. The combination of gas heating and heat pump provides security of supply, reduces operating costs and enables the gradual transition to renewable energy — particularly useful for unrenovated or only partially renovated old buildings.
When do I need a buffer tank?
A heat pump needs a buffer tankwhen the heating system fluctuates significantly, the heat requirement is irregular or frequent cycles should be avoided. A buffer tank is also useful for older radiators, several heating circuits or a combination with solar thermal energy.
Heat pump in old buildings — useful or not?
A heat pump in an old building makes sense if the building is well insulated, can be heated with low flow temperatures and suitable radiators are available. Even though the investment costs are higher than a simple boiler replacement, lower operating costs, government funding and climate friendliness speak in favour of the use in the long term. The heat pump is often used after just a few years. Alternatively, hybrid heating or a high-temperature heat pump can be economical in buildings with very high heat requirements.
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