Heat pump in an older building: which numbers matter?

Short answer #

Building age alone does not decide. Actual heat load, required flow temperature, achievable seasonal performance, emitters, electricity tariff and investment matter. Use a professionally assessed building and model ranges.

Important variables #

• Annual useful heat demand
• Flow temperature and heat emitters
• Realistic seasonal performance
• Investment including adaptations

Worked example #

20,000 kWh heat at SCOP 3.2 needs 6,250 kWh electricity. At SCOP 2.5 it needs 8,000 kWh, 1,750 kWh more each year.

Break-even: What changes the result? #

Lower flow temperatures and suitable emitters improve efficiency. High adaptation cost or an unfavourable electricity price moves the economic crossover.

Common mistakes #

• Using lab COP as annual performance
• Comparing energy cost only
• Omitting building adaptations

Sources & assumptions

• IEA PVPS — Photovoltaic Power Systems Programme (2026-08-17)
• RATIOXA — Methodology and formulas (2026-08-17)