Air Source Heat Pump vs Gas Boiler: The Honest Comparison for London Homeowners.
If you are weighing up an air source heat pump vs gas boiler for your London home, you have probably come across a lot of conflicting claims online. Some sources say heat pumps are dramatically cheaper to run. Others say they cost more. The honest answer is that it depends on your home, your tariff and how the system is installed. In this guide, we walk through the real 2026 numbers on running costs, efficiency, carbon emissions and overall value, so you can make an informed decision.
How Air Source Heat Pumps and Gas Boilers Actually Work
A gas boiler burns fuel to heat water directly. Modern condensing boilers operate at around 90 to 92% efficiency, meaning for every £1 of gas burned, roughly 90p becomes useful heat.
An air source heat pump works differently. Rather than burning fuel, it extracts heat from the outside air and concentrates it using a refrigeration cycle, similar to a fridge in reverse. The key measure of efficiency here is the Coefficient of Performance, or COP. A well-installed air source heat pump typically achieves a seasonal COP of 3.0 to 4.0, meaning for every 1 kWh of electricity used, it produces 3 to 4 kWh of heat. In percentage terms, that is 300 to 400% efficiency, several times more efficient than even the best gas boiler.
Running Costs: The Honest Numbers for 2026
This is where it gets genuinely interesting, and where a lot of marketing oversimplifies things. At current 2026 energy prices, electricity costs roughly 24 to 25p per kWh, while gas costs roughly 6 to 7p per kWh, meaning electricity is around 3.5 to 4 times more expensive per unit than gas.
On a standard variable electricity tariff, running costs for a heat pump and a gas boiler are often broadly similar, with some studies showing heat pumps costing slightly more, and others showing a small saving, depending on the property’s insulation and the heat pump’s COP. Industry modelling for a typical 3-bedroom home suggests gas boiler running costs of roughly £760 to £835 per year, compared with roughly £840 to £1,450 per year for a heat pump on a standard tariff, a wide range that reflects how much individual property factors matter.
On a dedicated heat pump electricity tariff, which offers a lower rate specifically for heat pump use, many homeowners see running costs fall to £200 to £400 per year less than a gas boiler. This is currently one of the most effective ways to make a heat pump more cost-effective to run.
In short:
- On a standard tariff: running costs are broadly comparable to a gas boiler, and may be slightly higher or lower depending on your property
- On a heat pump tariff: many homeowners see a saving of £200 to £400 per year
- With a correctly sized and optimised system: heat pumps perform at their best and the gap narrows further in their favour
We always recommend a proper heat loss survey before installation, as this is the single biggest factor in how well a heat pump will perform in your specific home. You can book a free assessment with our team to get an honest, property-specific picture before you commit.
Carbon Emissions: Where Heat Pumps Clearly Win
While running costs can be close, carbon emissions are not. According to data from DESNZ and the Energy Saving Trust, a gas boiler produces roughly 215g of CO2 per kWh of heat output, while an air source heat pump produces roughly 80g of CO2 per kWh, reflecting the lower carbon intensity of UK grid electricity combined with the heat pump’s efficiency multiplier.
For a typical home with an annual heat demand of around 12,000 kWh, that works out to roughly 2,580 kg of CO2 per year for a gas boiler, compared with roughly 960 kg for a heat pump, a reduction of around 60%. As the UK electricity grid continues to decarbonise, this gap is expected to widen further in favour of heat pumps over the coming years.
Installation Cost and the £7,500 Grant
Heat pumps cost more to install upfront. A gas boiler replacement typically costs £2,500 to £4,500, while an air source heat pump typically costs £8,000 to £15,000 before any grant. However, the £7,500 Boiler Upgrade Scheme grant significantly closes this gap, often bringing the net cost of a heat pump down to somewhere between £2,500 and £7,500, much closer to the cost of a new boiler. For a full breakdown of 2026 pricing, see our guide on heat pump installation costs in London.
Over a longer timeframe, typically 15 to 20 years, the combination of the grant, comparable or lower running costs on the right tariff, and significantly reduced emissions tends to favour heat pumps, particularly as gas prices are widely expected to rise over time while electricity prices may fall as more renewable generation comes online.
So, Which Should You Choose?
If your current boiler is nearing the end of its life, your home is reasonably well insulated, and you are able to switch to a heat pump-friendly electricity tariff, an air source heat pump is likely to make sense both financially and environmentally, especially with the £7,500 grant applied.
If your home has very high heat demand, or you are not in a position to review your electricity tariff, a heat pump may cost more to run on a like-for-like basis in the short term, though emissions savings would still apply. A correctly sized and optimised system makes a significant difference here, which is why we would always recommend a proper assessment first rather than relying on general figures.
As a Samsung approved installer with a 7-year warranty, and with installations typically completed in 2 to 3 days, we take the time to assess each property individually so you get an honest recommendation, not a one-size-fits-all answer.
Not sure if a heat pump is right for your home?
Get a free, no-obligation property assessment from our MCS certified team. We will give you an honest recommendation based on your home, not a generic estimate, including your eligible grant amount.
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By Matthew Fasami