Air conditioning vs gas boiler: which is cheaper to run? (UK, 2026)
Most people think of air conditioning as a summer-only appliance. In fact, modern split systems are air-source heat pumps that heat and cool — and in a lot of UK homes they now beat a gas boiler on running cost. Here's the honest comparison at 2026 prices.
The key number: coefficient of performance (COP)
A modern A+++ split air conditioner has a COP of around 4.0 for heating. That means for every 1 kWh of electricity it draws, it delivers around 4 kWh of heat. A gas boiler, by contrast, has an efficiency of 88–92% — for every 1 kWh of gas you pay for, you get 0.88–0.92 kWh of heat.
That 4x multiplier is why AC heating can be dramatically cheaper than gas, despite electricity being more expensive per kWh.
The maths at 2026 UK prices
Ofgem energy price cap (mid-2026, indicative): 27p/kWh electricity, 7p/kWh gas.
| To deliver 10 kWh of heat | Energy used | Cost |
|---|---|---|
| Gas boiler (90% efficient) | 11.1 kWh gas | £0.78 |
| A+++ air-con heat pump (COP 4.0) | 2.5 kWh electricity | £0.68 |
The AC comes out ~13% cheaper for heating, per kWh delivered. In shoulder seasons (spring, autumn) when the COP is even better, savings widen to 20–25%.
Where AC really wins
- Heating a single room instead of firing up the whole house's central heating for one cold snug or bedroom
- Home offices — you're only heating the room you're in
- Extensions where extending the wet central heating is expensive
- Loft conversions where radiator plumbing is a pain
- Shoulder seasons (April, May, September, October) where boiler efficiency drops off
Where gas still wins
- Whole-house heating in a poorly-insulated older property
- Hot water — AC doesn't do hot water; you still need a boiler or immersion
- Very cold days (below 0°C) where AC COP drops to ~2.5 and it gets closer to gas
Cooling — no contest
A boiler obviously can't cool. In a UK summer with 30°C+ heatwaves becoming yearly, cooling is where AC pays for itself in sleep and productivity alone. A bedroom unit running overnight (8 hours) costs around £0.24–£0.40 — cheaper than a pint.
The practical setup most Midlands homes go for
Keep the gas boiler for hot water and background heating in winter. Add air conditioning to the rooms you actually live in — lounge, main bedroom, home office. You get cheap zonal heating year-round plus proper cooling in summer, without ripping out anything you already have.
FAQ
Do I need to replace my boiler if I install AC?
No. Most customers keep the boiler for hot water and background heat, and use AC for zonal heating and summer cooling.
What about heat pumps for hot water?
Different product — an air-to-water heat pump. Split air-con systems (air-to-air) heat and cool the room, not your hot water tank.
Does the COP really hold up in winter?
Modern inverter units maintain COP > 3 down to about 2°C. Below freezing it dips, but the Midlands rarely stays sub-zero for long stretches.
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