How much CO2 does a gas boiler produce?

Natural gas produces 183g CO2 per kWh burned. A typical UK home using 12,000 kWh of heat per year with a 92% efficient condensing boiler produces approximately 2,400 kg (2.4 tonnes) of CO2 annually. Older non-condensing boilers produce more due to lower efficiency.

How much CO2 does a heat pump produce?

A heat pump uses electricity, which has a UK grid carbon intensity of approximately 136g CO2/kWh (2024 average). With a COP of 3.0, the effective carbon intensity is about 45g CO2 per kWh of heat — around 75% less than a gas boiler. As the grid decarbonises, this improves further.

What is the grid decarbonisation effect?

The UK electricity grid is getting cleaner each year as more renewable generation is added. The carbon intensity has fallen from 500g/kWh in 2012 to around 136g/kWh in 2024. By 2035, the government targets a fully decarbonised grid. This means heat pumps get greener every year, while gas boilers remain constant.

How many trees does it take to offset a gas boiler?

A mature broadleaf tree absorbs approximately 22 kg of CO2 per year. A typical gas-heated home produces around 2,400 kg CO2/year, so you would need approximately 109 mature trees growing year-round to offset one gas boiler. Switching to a heat pump saves the equivalent of planting 80+ trees.

Are heat pumps really lower carbon than gas boilers?

Yes, even with current UK grid carbon intensity. A heat pump with SCOP of 3.0 using grid electricity at 136g/kWh produces about 45g CO2 per kWh of heat, compared to 199g for a 92% efficient gas boiler. The heat pump is already 77% lower carbon, and this gap widens as the grid decarbonises.

TradeCalculator

Carbon Offset Calculator — Heat Pump vs Gas Boiler

Compare CO2 emissions from your gas boiler versus a heat pump. See annual and cumulative carbon savings, equivalent trees, and grid decarbonisation effects.

Annual Heat Demand

From gas bill or EPC

Current Boiler Type

Heat Pump Type

Projection Period

Years to project cumulative savings

How We Calculate This

This calculator compares the carbon dioxide emissions from your current boiler with a heat pump replacement, showing both annual savings and cumulative impact over 20 years.

Carbon calculation

Gas boiler CO2: (Heat demand / boiler efficiency) x 183g CO2/kWh
Heat pump CO2: (Heat demand / SCOP) x grid carbon intensity
Annual saving: Boiler CO2 - Heat pump CO2
Grid decarbonisation: Grid carbon factor reduces ~5% per year, improving HP savings

Frequently Asked Questions

Related Calculators

Air Source Heat Pump Sizing Calculator

Size air source heat pumps from whole house heat loss with defrost derating.

Ground Source Heat Pump Calculator

Calculate ground source heat pump borehole depth or trench pipe loops per kW.

Heat Pump COP Calculator

Calculate heat pump COP and seasonal COP with running cost comparison vs gas.

Heat Pump Radiator Calculator

Re-size radiators for heat pump 45C flow with de-rating factor.

Solar PV Array Calculator

Calculate solar PV array size, orientation yield factor and annual kWh by UK region.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.