Is a heat pump lower carbon than a gas boiler?
Delivered heat is the fair unit: a boiler wastes some of the gas it burns, a heat pump multiplies the electricity it uses.
Compared on: 10,000 kWh of delivered heat per year (typical UK home)
Gas condensing boiler
2.20 t CO₂e~11,100 kWh of gas at 90% efficiency, at ~0.20 kg CO₂e/kWh including upstream.
Source: DEFRA/DESNZ UK conversion factors — natural gas
Air-source heat pump (UK grid)
750 kg CO₂e~3,300 kWh electricity at a seasonal performance factor of 3.0.
Source: DEFRA/DESNZ grid electricity factors
Direct electric heating (UK grid)
2.25 t CO₂e1 kWh in, 1 kWh out — no multiplication, so it lands near gas.
Source: DEFRA/DESNZ grid electricity factors
What this means
- A heat pump is around 3× lower carbon than gas on today's UK grid, and improves every year as the grid decarbonises.
- Direct electric resistive heating is not an improvement on gas — the efficiency multiplier is what does the work.
- Insulation cuts the kWh of heat needed in the first place, which helps whichever system you have.
Your own number, not an average
Averages answer the question; your own footprint tells you what to change first. The calculator takes about two minutes and needs no account.
Figures are averages drawn from public databases and peer-reviewed LCA work; see our methodology for how each factor is applied.