How Much Carbon Does Switching to a Heat Pump Actually Save?

Switching from a gas boiler to a heat pump is one of the most impactful individual actions a UK homeowner can take to reduce their personal carbon footprint. But exactly how much carbon does it actually save? The answer depends on the carbon intensity of the electricity grid, your home's heating demand, and the efficiency of your heat pump. Here is how to calculate the real saving for your home — and why the number keeps improving.

The grid carbon intensity figure

The carbon saving from a heat pump depends heavily on how much CO₂ is emitted per kWh of electricity you consume. This is the grid carbon intensity, measured in grams of CO₂ per kilowatt-hour (gCO₂/kWh). The UK grid has decarbonised rapidly: in 2012, grid intensity was approximately 500 gCO₂/kWh; by 2025, it had fallen to approximately 150 gCO₂/kWh as coal was phased out and renewable capacity expanded.

DESNZ uses a figure of approximately 136 gCO₂/kWh for 2025 electricity in standard energy assessments (the SAP 10.2 emissions factor). This compares to 215 gCO₂/kWh for natural gas. The implication: electricity is already significantly lower carbon per kWh than gas, and this gap will widen as the grid continues to decarbonise toward the government's 2035 clean power target.

Calculating the carbon saving

For a 3-bedroom semi-detached home with 12,000 kWh annual heating demand, the carbon emissions comparison works as follows:

Even at a modest SCOP of 3.0, a heat pump reduces heating carbon by approximately 81% versus a gas boiler. At SCOP 3.5, the reduction is 84%. For a home switching from oil heating (approximately 265 gCO₂/kWh effective), the savings are even larger: a heat pump at SCOP 3.5 cuts heating carbon by approximately 87%.

Why the saving keeps improving

The carbon saving from a heat pump is not fixed — it improves automatically as the electricity grid decarbonises. A heat pump installed today at SCOP 3.5 achieves an 84% carbon reduction versus gas. By 2030, if grid intensity falls to 50 gCO₂/kWh (consistent with the government's Clean Power by 2035 trajectory), the same heat pump achieves approximately 95% carbon reduction. A gas boiler installed today, by contrast, becomes more carbon-intensive relative to a decarbonising grid every year.

This dynamic means the carbon case for heat pumps strengthens over time without any change to the equipment. It also means that delaying a switch from gas to a heat pump has a compounding carbon cost: every year of continued gas boiler use involves emissions that could have been avoided.

Comparing to other carbon reduction actions

To put the heat pump carbon saving in context:

• •Switching from a gas boiler to a heat pump: saves approximately 2,400 kg CO₂/year (3-bed semi)
• •Switching from a petrol car to an EV: saves approximately 1,100–1,500 kg CO₂/year (average mileage)
• •Eliminating one long-haul return flight: saves approximately 1,500–2,500 kg CO₂
• •Installing solar PV (4 kWp system): saves approximately 900–1,200 kg CO₂/year

Switching heating from gas to a heat pump is typically the single largest carbon reduction available to a UK homeowner — larger than switching to an EV, and achieved in a home context that requires no lifestyle change beyond the initial installation.

Refrigerant leakage: the caveat

Heat pump refrigerants — typically R32 or R410A — are potent greenhouse gases if released. A small refrigerant leak from a poorly maintained or damaged system can release the equivalent of several tonnes of CO₂. This is why the F-Gas regulations require refrigerant handling only by certified engineers, and why annual servicing (which includes a refrigerant pressure check) is important not just for efficiency but for environmental integrity. A well-maintained heat pump with no refrigerant leaks has the full carbon benefit described above; a leaking system can significantly erode it.

Heat pumps and renewable electricity

If you pair a heat pump with a home solar PV system or a 100% renewable electricity tariff, the carbon saving increases further. Solar generation directly offsets the electricity consumed by the heat pump on sunny days, with the grid-average emissions factor applying only to grid electricity consumed outside solar generation hours. For homes with 4 kWp of solar, the effective carbon factor of electricity consumed by the heat pump can fall below 80 gCO₂/kWh on an annual average basis.