Energy and running costs
Annual carbon saving: heat pump compared with a gas boiler
- where
- heat pump emissions (kgCO₂e/yr)
- annual heat demand (kWh/yr)
- seasonal performance, SCOP or SPF
- electricity emission factor (kgCO₂e/kWh)
- gas boiler emissions (kgCO₂e/yr)
- boiler seasonal efficiency (%)
- natural gas emission factor (kgCO₂e/kWh)
- annual carbon saving (kgCO₂e/yr)
Explain this equation
Compares the yearly carbon emissions of a heat pump and a gas boiler supplying the same heat.
Energy used is worked out as for running costs: heat demand divided by SCOP for electricity, or by boiler efficiency for gas. Each is then multiplied by its emission factor, the kilograms of CO₂ equivalent released per kWh of that fuel. The government publishes these factors each year; the electricity one includes losses in the grid.
Emissions are fuel use times emission factor.
Sense check: 15,500 kWh gives about 720 kg a year for the heat pump against about 3,140 kg for the boiler, a saving of about 2.4 tonnes.
Watch out: the electricity factor falls as the grid decarbonises, so use the current year's figure. Use the gross CV gas factor to match how gas is billed.
Estimates the yearly greenhouse gas emissions of a heat pump and a gas boiler meeting the same heat demand, and the saving.
Enter your values to see the result.
Good to know
Defaults are the UK Government GHG conversion factors 2026 (DESNZ): electricity generation 0.13096 plus transmission and distribution losses 0.01299, published as 0.14396 kg CO2e/kWh consumed (the parts are rounded), and natural gas 0.18231 kg CO2e/kWh on a gross calorific value basis (the basis used on gas bills). These are average factors for company reporting; SAP 10 and the Home Energy Model use their own factors, so EPC figures will differ.
Common mistake
Using an old grid factor. The 2026 electricity factor is about 26% lower than the 2025 one, so older figures understate the saving.
Limits
Annual average factors only; no refrigerant leakage, manufacture or time-of-use carbon intensity.
Sources
- DESNZ Greenhouse gas reporting: conversion factors 2026 (UK electricity generation 0.13096 and T&D 0.01299 kg CO2e/kWh; natural gas 0.18231 kg CO2e/kWh gross CV)
- EnergyCount: UK carbon conversion factors 2026, buildings and energy (restates the DESNZ 2026 values)
- BS EN 14825 Air conditioners, liquid chilling packages and heat pumps: testing and rating at part load and calculation of seasonal performance (SCOP)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow MCS standards, manufacturer data, BS 7671, the ENA connection rules and Building Regulations. System design and DNO applications need a competent, certified installer.