Combine seasonal COP and heat demand

Short answer #

Electricity demand equals useful heat divided by seasonal COP. Use building-specific heat demand and test COP as a range; a laboratory COP is insufficient.

Important variables #

• Investment after support
• Useful energy, efficiency and degradation
• Energy prices and tariff
• Horizon and discount rate

Worked example #

20,000 kWh heat needs about 5,000 kWh electricity at COP 4.0, or 7,143 kWh at COP 2.8.

Break-even: What changes the result? #

Test the main driver as a cautious, central and optimistic range. Also check whether the ranking reverses at a crossover or remains robust across the range.

Common mistakes #

• Treating subsidy or tariff as certain
• Omitting losses and degradation
• Confusing simple payback with return

Sources & assumptions

• KfW Bankengruppe — Heizungsförderung ab 21. Juli 2026 (2026-08-17)
• RATIOXA — Methodology and formulas (2026-08-17)