Carbon Offset Calculator — Heat Pump vs Gas Boiler

Mains gas carries a carbon factor of 210g CO2 per kWh under SAP 10.2 (the UK Building Regulations / EPC basis). A typical UK home using 12,000 kWh of heat per year with a 92% efficient condensing boiler produces approximately 2,740 kg (2.7 tonnes) of CO2 annually. Older non-condensing boilers produce more due to their lower efficiency. (For corporate GHG reporting, DESNZ quotes 183g CO2 per kWh for the gas itself, before boiler losses.)

A heat pump uses electricity, which has a SAP 10.2 carbon factor of 136g CO2/kWh (annual UK average). With a SCOP of 3.0, the effective carbon intensity is about 45g CO2 per kWh of heat — around 80% less than a 92% efficient gas boiler. As the grid decarbonises, this improves further.

The UK electricity grid gets cleaner each year as more renewable generation is added. The carbon intensity of generation has fallen from around 500g/kWh in 2012 to roughly 125–170g/kWh by 2024. The government’s Clean Power 2030 Action Plan (December 2024) targets at least 95% low-carbon electricity and a generation carbon intensity well below 50g CO2e/kWh by 2030. This means heat pumps get greener every year, while gas boilers stay constant.

A mature broadleaf tree absorbs approximately 22 kg of CO2 per year. A typical gas-heated home produces around 2,740 kg CO2/year, so you would need roughly 125 mature trees growing year-round to offset one gas boiler. Switching to a heat pump saves the equivalent of about 100 trees planted (this is an illustrative rule of thumb, not a formal sequestration figure).

Yes, even at current UK grid carbon intensity. A heat pump with a SCOP of 3.0 using grid electricity at 136g/kWh produces about 45g CO2 per kWh of heat, compared with about 228g for a 92% efficient gas boiler (210g/kWh gas ÷ 0.92). The heat pump is already around 80% lower carbon, and this gap widens as the grid decarbonises.