Heat Pumps in Older Buildings: What Works, What Doesn't?
"A heat pump in an older building won't work": this sweeping statement is wrong. It dates from a time when heat pumps really did only run efficiently in well-insulated new builds with underfloor heating. Modern units now reach significantly higher flow temperatures and can therefore also cope with conventional radiators: in most older buildings, a heat pump works as long as you keep a few points in mind.
What matters is an honest assessment of the existing building: how high is the building's heat load, what flow temperature do the existing heating surfaces need, and where are the structural limits? This guide shows you the possibilities and limits, including costs and funding. The key figures up front: 60 to 80% of older buildings are suitable for a heat pump, the maximum BEG funding (Germany's Federal Funding for Efficient Buildings) is 70%, and the typical payback period is 15+ years.
Requirements: when is an older building suitable?
Whether a heat pump runs economically in an older building essentially depends on a single question: can the building be kept warm with moderate flow temperatures? Heat pumps work more efficiently the smaller the temperature difference between the heat source and the heating water. A house that manages with a maximum flow temperature of 55 °C is therefore a good candidate; a house that does not get properly warm even at 70 °C is not, at least not without preparatory work.
Incidentally, you can test the flow temperature in a very practical way before you invest: on a cold winter day, set your existing heating system to a flow temperature of 55 °C and observe whether all rooms get sufficiently warm. If the house stays comfortable, the most important hurdle has been cleared. Practical factors also play a role: from space for the outdoor unit and the capacity of the power connection to the noise sensitivity of the neighborhood.
Suitable if
- Heat load below 8 kW
- Flow temperature of max. 55 °C possible
- Radiators large enough or underfloor heating in place
- Building power connection of at least 24 kW
- Space for the outdoor unit (3 m²)
Difficult with
- Heat load above 12 kW (very poorly insulated)
- Only small panel radiators
- A power connection that cannot be upgraded
- A listed building with design requirements
- A noise-sensitive neighborhood
Which heat pump for an older building?
Not all heat pumps are the same: the systems differ above all in the heat source from which they draw their energy. The air-to-water heat pump uses outdoor air and is the easiest to install, but in return it has to work hardest precisely when it is coldest outside. Ground and groundwater, on the other hand, offer stable temperatures all year round and therefore better seasonal performance factors (SPF), but this comes at the price of drilling, permit procedures and higher investment costs.
In practice, the air-to-water heat pump is the most common route for older buildings, because it requires no earthworks and can also be realized on smaller plots. If you have the option of a ground probe and take a long-term view, the brine variant is often the more efficient choice. The overview shows the strengths and weaknesses of the systems:
| Type | Advantages | Disadvantages |
|---|---|---|
| Air-to-water HP | Affordable, simple | Louder, efficiency drops in winter |
| Brine-to-water (ground probe) | Highly efficient, quiet | More expensive (drilling), permit required |
| Water-to-water (well) | Highest SPF | Permit required, not possible everywhere |
| Ventilation with active heat recovery (Nilan) | Combination: ventilation, heating, hot water | Duct routing is difficult in older buildings |
You can read more about combining ventilation and heat pumps in the guide to comfort ventilation with heat recovery. You will find suitable units in the Heat Pumps category.
Preparing an older building: step by step
The most common mistake in a heat pump project in an older building is impatience: anyone who orders the unit straight away without first having the heat load and heating surfaces checked risks an incorrectly sized system, which either works inefficiently or cannot maintain living comfort. An oversized heat pump cycles frequently and wears out faster; an undersized one cannot keep the house warm on cold days.
A sound sequence therefore always starts with the calculation: only once it is established in black and white how much heat the building really needs, and whether the existing radiators can deliver this heat at low flow temperatures, should specific units be discussed. At the same time, it pays to look at the infrastructure: the power connection, installation location and noise protection are best clarified early on, while alternatives are still open.
- Heat load calculation according to DIN EN 12831 by an energy consultant (mandatory for BEG funding)
- Heating surface check: are the existing radiators sufficient at a flow temperature of 55 °C? This includes hydronic balancing with calculation
- Check the insulation status: is the roof insulated? Are the windows at least double-glazed? If not, insulate first
- Power connection: 24 to 32 kW is often required; if necessary, upgrade the building connection (at a charge)
- Outdoor installation: minimum distance of 3 m from the neighboring property line, comply with sound levels according to TA Lärm (German Technical Instructions on Noise Protection)
Note: For very old houses (built before 1980, uninsulated), you should prioritize insulation first. Then the heat pump suddenly makes sense.
Costs and funding 2026
Investing in a heat pump in an older building is noticeably more expensive than installing a new gas or oil boiler. Nobody should gloss over that. In existing buildings, the unit itself often comes with additional costs that do not arise at all in new builds: upgrading the power connection, replacing individual radiators that are too small, or the mandatory hydronic balancing. If you plan for these items from the outset, you will not face any nasty surprises later on.
On the other side are the generous government subsidies, which cushion a considerable part of the additional costs, and the ongoing savings compared with fossil fuels over the entire service life of the system. The typical cost blocks at a glance:
| Item | Costs |
|---|---|
| Air-to-water HP, complete | €20,000 to €30,000 |
| Brine HP with drilling | €30,000 to €50,000 |
| Hydronic balancing | €500 to €1,500 |
| Upgrading the power connection | €1,500 to €5,000 |
| Replacing heating surfaces (if necessary) | €3,000 to €8,000 |
| Total investment | €25,000 to €65,000 |
With 70% BEG funding, the effective out-of-pocket costs are €7,500 to €19,500. You can read all the details in the 2026 funding guide. You will find accessories for integration into the heating system under Heating Pipes and Press Fittings.
Frequently asked questions
Does a heat pump really work in an older building?
Yes, in 60 to 80% of older buildings. Requirements: a heat load below 8 kW and the ability to heat with a flow temperature of max. 55 °C. A practical test with the existing heating system in winter quickly provides clarity.
Do I need new radiators?
Not necessarily. If the existing radiators deliver sufficient output at a flow temperature of 55 °C (calculation required!), the existing system will work. Often it is enough to replace just a few critical radiators with larger models.
How much electricity does a heat pump need in an older building?
An SPF of 3.0 to 4.0 is typical in older buildings. With a heating energy demand of 20,000 kWh, that means 5,000 to 6,700 kWh of electricity.
Can I combine the heat pump with my old heating system?
Yes, a "hybrid heating system" is permitted. The heat pump covers the base load, and the old heating system steps in at peak load. This can be a sensible interim solution if the building is being renovated step by step.
Conclusion
A heat pump in an older building is feasible in most cases: what matters are the heat load, the flow temperature and adequately sized heating surfaces. If you have a proper heat load calculation carried out before investing and limit your existing heating to a flow temperature of 55 °C as a test in winter, you will quickly know where you stand. With up to 70% BEG funding, out-of-pocket costs fall significantly, so the project can also pay off economically. And even if the building is not ready yet: with targeted insulation and hydronic balancing, almost any older building can be made heat-pump-ready step by step.
You will find heat pumps and accessories in the heating range at wohnungstechnik.de.
