Can You Install a Heat Pump in Any Old Building?
The short answer: Yes, in principle, a heat pump can be installed in almost any building. The decisive question is not whether, but under what conditions it operates efficiently and economically. In a well-insulated old building with an adapted heating system, a heat pump can work just as efficiently as in a new build. In an unrenovated old building with small radiators and high heating demand, however, it can become uneconomical.
The Three Decisive Factors in Old Buildings
Three factors determine whether a heat pump makes sense in your old building: the flow temperature of the heating system, the building's heating demand, and the heating surfaces (radiators or underfloor heating).
Flow temperature is the most important parameter. Heat pumps operate most efficiently at low flow temperatures up to 45 degrees Celsius. Underfloor heating requires only 30 to 35 degrees, large radiators 40 to 50 degrees. Old, small radiators in unrenovated old buildings, however, often require 55 to 70 degrees to adequately heat the rooms. At these high temperatures, the seasonal COP drops to 2.0 to 2.5, and operating costs increase considerably.
Heating demand indicates how much energy the building needs for heating. In an unrenovated old building (pre-1970), the specific heating demand often lies at 150 to 250 kWh per square meter per year; in a well-renovated building at 50 to 100 kWh. The higher the heating demand, the more electricity the heat pump consumes and the higher the operating costs.
Heating surfaces must be large enough to deliver sufficient heat at low flow temperatures. In old buildings, radiators are often undersized for operation with a heat pump. Replacing them with larger radiators or installing underfloor heating can solve this problem.
Which Renovation Measures Should You Tackle First?
Before installing a heat pump, energy consultants frequently recommend the following measures in this order based on cost-benefit ratio.
First: Hydraulic balancing (500 to 1,500 euros). The most effective and cheapest measure that optimizes heat distribution and can lower the flow temperature. Second: Roof insulation (15,000 to 25,000 euros for a typical single-family home). Up to 30 percent of heating energy escapes through an uninsulated roof. Roof insulation is often simpler and cheaper than facade insulation.
Third: Window replacement (800 to 1,500 euros per window). Old single-glazed or leaky windows cause major heat losses. Triple glazing significantly reduces heating demand and drafts. Fourth: Facade insulation (150 to 300 euros per square meter). The most effective but also most expensive single measure. Reduces heating demand by 20 to 40 percent.
Fifth: Radiator replacement or underfloor heating (3,000 to 15,000 euros). If after insulation the flow temperature is still above 50 degrees, replacing radiators with larger models or retrofitting underfloor heating is advisable.
What Does the Energy Consultant Say?
Before installing a heat pump in an old building, consultation with a certified energy consultant is strongly recommended. The consultant creates an individual renovation roadmap (iSFP) that shows the optimal sequence and combination of measures. The cost of the iSFP (1,500 to 2,500 euros) is subsidized at 80 percent by BAFA, and the iSFP adds an extra 5 percent bonus to the BEG subsidy.
Case Study: Old Building from 1965
A typical case: Terraced house, built 1965, 120 square meters, oil heating with 25,000 kWh consumption, small radiators, no insulation standard. Without renovation, the effective COP would be only 2.2, electricity costs would be approximately 3,400 euros per year, more than the previous oil costs.
After partial renovation (roof insulation, window replacement, radiator enlargement), heating demand drops to 16,000 kWh, flow temperature to 45 degrees, and the effective COP rises to 3.2. Electricity costs then amount to approximately 1,500 euros per year, well below the previous oil costs of 2,750 euros. The combination of renovation and heat pump thus saves 1,250 euros per year while simultaneously improving living comfort.
Conclusion: Insulate First, Then Pump
The golden rule for heat pumps in old buildings is: First improve the building envelope, then install the heat pump. Investment in insulation pays off twice: through lower heating demand and through a higher COP for the heat pump. Use our calculator with different insulation settings to see the effect of renovation on economic viability.