Heat pump or gas boiler: comparing running costs, CO₂ and the law
Since 29 July 2026 both are allowed on equal terms in Germany. The difference lies in running costs, the CO₂ price, the biogas duty and the grant.
Worked through by Radif Partners · Editorial policy · How we calculate
Gas or heat pump, per year
Heat pump saves a year
€1,054
| Gas boiler | €2,316 |
| Heat pump | €1,262 |
| Heat pump electricity | 4,600 kWh |
Gas 12 ct, heat pump power 27 ct, SPF 3.
Since the Building Modernisation Act (Gebäudemodernisierungsgesetz) took effect, the choice between a heat pump and a new gas boiler is no longer settled by a percentage rule but by the numbers. For a household using 20,000 kWh of gas a year, a gas boiler at the official Destatis average of 11.58 ct per kWh costs €2,316 a year. An air-source heat pump with the seasonal performance factor measured in existing homes, 3.4, needs 4,600 kWh of electricity for the same heat and costs €1,262 on a heat pump tariff. That is €1,054 less each year. Three further points concern the gas boiler only. It emits about 3,628 kg of CO₂ a year, priced from 2028 in EU emissions trading without a fixed corridor. A gas boiler installed after 29 July 2026 must cover 10 % of its heat with biomethane or hydrogen from 2029 and 60 % from 2040 (section 43). And only the heat pump gets a grant: replacing a 25-year-old gas boiler, a household with €75,000 income receives €12,880.
Equally allowed, unequally expensive
Until 28 July 2026, the Building Energy Act required new heating to run on 65 % renewable energy once certain deadlines had passed. The act of 23 July 2026 removed that requirement. Today the gas boiler stands next to the heat pump in the list of section 42 of the Building Modernisation Act, and both are permitted. The decision therefore moves from the law to your own sums, where four items pull apart: the fuel, the CO₂ price, the green gas duty and the grant. If you are buying a German house with an old gas boiler, this is the comparison to make before you sign with an installer.
Running costs compared
The starting point is the consumption on your gas bill. From it the engine works out the heat the house actually needs and, for the heat pump, divides it by the SPF from the Fraunhofer ISE field study. For 20,000 kWh of gas a year:
| System | Energy a year | Cost a year | CO₂ a year |
|---|---|---|---|
| Gas boiler, 11.58 ct/kWh | 20,000 kWh gas | €2,316 | 3,628 kg |
| Air-source heat pump, SPF 3.4 | 4,600 kWh electricity | €1,262 | 0 kg at the house |
| Ground-source heat pump, SPF 4.3 | 3,637 kWh electricity | €998 | 0 kg at the house |
At constant prices, the air-source heat pump earns back €10,538 against the gas boiler over ten years. If, after the grant, it costs less than that amount more than a new gas boiler, it pays for itself within that time. The heat pump cost calculator uses your own figures.
The CO₂ price: a corridor in 2026, open afterwards
Every kWh of gas carries a CO₂ price. For 2026, section 10 of the Fuel Emissions Trading Act sets a corridor of €55 to €65 per tonne, and auctions averaged €65. That is about 1.40 ct per kWh including VAT. For 2027 the Bundestag voted on 15 October 2026 for the same corridor; the law has not yet been promulgated. From 2028, the EU emissions trading for buildings is due to apply, without a fixed price. Nobody knows how the price will move then. The values below are scenarios, not a forecast:
| CO₂ price per tonne | Extra cost of gas a year |
|---|---|
| €100 | €151 |
| €150 | €367 |
| €200 | €583 |
The heat pump carries no such surcharge; its risk lies in the electricity price. The state of play for 2027 and 2028 is summed up under CO₂ price 2027.
The biogas steps for new gas boilers
Choosing a new gas boiler brings a duty under section 43 of the Building Modernisation Act: a growing share of the heat must come from biomethane, biogenic LPG or hydrogen. For the household using 20,000 kWh a year, that means:
| From | Required share | Green gas a year | Per cent of surcharge |
|---|---|---|---|
| 1 January 2029 | 10 % | 2,000 kWh | €20 |
| 1 January 2030 | 15 % | 3,000 kWh | €30 |
| 1 January 2035 | 30 % | 6,000 kWh | €60 |
| 1 January 2040 | 60 % | 12,000 kWh | €120 |
Required share for your new gas boiler
Required from 2030
15 %
| Green gas a year | 2,700 kWh |
| Extra cost at your premium | enter a premium |
Applies to gas, oil and LPG boilers installed after 29 July 2026.
If you do not want to meet the duty through your gas tariff, the law allows, among other routes, adding a heat pump with at least 30 % of the boiler output. Older gas boilers that were running before 29 July 2026 are not affected. Exceptions and the deadlines after a breakdown are covered under gas boiler ban.
Where the sums are uncertain
Three assumptions carry the comparison, and none of them is fixed. First the SPF: air-to-water systems in the measurements ranged from 2.6 to 4.9, which in the example means €876 to €1,651 of electricity a year. Second the heat pump tariff: the Federal Network Agency figure dates from 1 April 2025, and no newer official survey exists. Third the gas price, an average across all contracts including the standing charge, which will not match your own tariff exactly. Enter your consumption and your own CO₂ scenario in the calculator above. Whether a heat network is planned for your street no longer obliges you to anything since 29 July 2026, but it may open a third option.
Grant and letting
For a heat pump KfW pays at least 30 % of up to €28,000 in eligible costs, for a gas boiler nothing (guideline of 17 August 2026). In the example, a €32,000 quote, a 25-year-old gas boiler and €75,000 income, the grant is €12,880 because the 16 % climate speed bonus is added. Your own case is calculated under heat pump grant. Landlords must, under the CO₂ cost allocation act, bear half the CO₂ costs of a new gas boiler from 2028; with a heat pump that item disappears. The split under the stage model for existing systems is shown by the cost split calculator.