Heating Cost Comparison Calculator 2026

Yes. Since 29 July 2026 the Building Modernisation Act (GModG) has applied, and the former duty to use 65 % renewable energy when replacing a heating system is gone. You may install a new gas boiler again. From 2029, however, it must use a rising share of biomethane or hydrogen (the Bio-Treppe), and it gets no funding.

The Bio-Treppe (bio-ladder) is set out in § 43 GModG. Gas and oil boilers installed in an existing building after 29 July 2026 must cover at least 10 % of their heat from biomethane, bio-oil, biogenic LPG or hydrogen from 2029, 15 % from 2030, 30 % from 2035 and 60 % from 2040. Until 2034 a solar thermal system or ventilation with heat recovery also counts. Existing boilers are not affected.

Yes. A hybrid system meets the duty if its heat pump covers at least 30 % (bivalent parallel) or 40 % (bivalent alternative) of the peak-load boiler’s output (§ 43(5) GModG). For hybrid units only the heat pump share is funded, and there is no climate speed bonus because gas is still used. This version of the calculator does not yet compare hybrid systems.

Often yes, as long as the flow temperature is not too high. With classic radiators up to 55 °C we assume a seasonal performance factor of 3.0, with underfloor heating 4.0. Replacing just a few radiators can lower the temperature needed. In the worked example on this page, the air-source heat pump is the cheapest option over 20 years in a detached house using 20,000 kWh of gas with classic radiators.

KfW funds heat pumps, pellet boilers and district heating connections at 30 % (programme 458). If they apply by 31 January 2027, owner-occupiers get another 16 percentage points of climate speed bonus for replacing a working oil, coal, gas-per-flat or night storage heating, or a gas boiler at least 20 years old. An income bonus of 10 to 40 points applies for household incomes up to €50,000. The total is capped at 70 %, or 80 % for incomes up to €30,000. For the first unit, at most €28,000 of costs are eligible.

From the first quarter of 2027 the base rate for heat pumps falls to 15 %. Heat pumps of EU origin get a 15 point value-added bonus and so stay at 30 %. A KfW information sheet will set the exact date and definition. The climate speed bonus also drops to 12 % from 1 February 2027, and eligible costs fall to €27,250. The application date is what counts.

For gas and oil boilers installed after 29 July 2026, landlords pay half of the CO₂ price and gas network fees from 2028, and from 2029 half of the extra cost of the bio share, limited to a 30 % share (§ 5a CO2KostAufG). For existing boilers the tiered model based on CO₂ emissions per square metre still applies. There are hardship rules for small landlords and owner-occupied two-family houses (§ 5d) that the calculator does not model.

Yes, as a modernisation under § 559e BGB. Since 29 July 2026, § 559f BGB generally requires proof of a seasonal performance factor of at least 2.5. Without it, only half of the cost counts. Exceptions include buildings built after 1996 or that can be heated with a flow temperature of 55 °C or less. For a new fossil boiler under § 43 GModG the flat 15 % deduction for avoided maintenance no longer applies.

In 2026 a tonne of CO₂ from heating costs €55 to €65; we use €60. A government bill proposes the same corridor for 2027. From 2028 the EU emissions trading system ETS 2 applies and the market sets the price. The calculator uses three scenarios for it, with €100 in 2030 and €150 in 2035 in the medium scenario. A bill on a green gas quota from 2045 is due by 1 December 2026.

No. The duty to replace boilers older than 30 years has been gone since 29 July 2026 (§ 72 GModG repealed). You may keep running and repairing a working boiler. If you switch while the old boiler still works, you get the climate speed bonus, which steps down from February 2027.

The seasonal performance factor (SPF, in German Jahresarbeitszahl or JAZ) shows how much heat a heat pump makes from one kilowatt hour of electricity over a year. An SPF of 3.5 means 1 kWh of electricity gives 3.5 kWh of heat. It depends mainly on the flow temperature and the heat source. Ground-source heat pumps reach higher values than air-source ones because the ground is warmer than the outside air in winter.