TL;DR
UK households use significantly more electricity during heatwaves. The largest demand drivers are portable and fixed air conditioning, fans running for extended periods, and increased compressor cycling in fridges and freezers in warm kitchens. The Ofgem standing charge does not change with weather, but unit consumption rises sharply and the bill follows. Targeted measures cut consumption faster than tariff switching during short events.
Last reviewed: 2 June 2026
A UK heatwave lifts household electricity bills through a small number of large drivers and a lot of small ones. The standing charge and unit rates set by Ofgem do not change with the weather, but consumption rises sharply. For households on the default tariff cap, the difference between a 28C summer and a 32C summer can mean tens of pounds across a month. The largest savings come from targeted operating changes, not tariff switching.
Key facts
- A typical portable air conditioning unit uses 0.7 to 1.5 kWh per hour of operation.
- A pedestal fan uses around 0.05 to 0.08 kWh per hour, far less than air conditioning.
- Fridge and freezer compressors cycle more often in warm kitchens, lifting baseline load.
- The Ofgem default tariff cap sets unit and standing charge rates. Weather does not change the cap directly.
- The Department for Energy Security and Net Zero produces guidance on staying cool affordably.
Where the extra electricity goes
The three largest heatwave drivers in a typical UK home are air conditioning, fans, and the refrigeration cycle. A 1.5 kW portable air conditioner running 8 hours a day for a week uses around 84 kWh, which on a standard cap unit rate adds roughly GBP 25 to the bill before standing charge. A pedestal fan running the same hours uses about 4 to 5 kWh in the same week, around GBP 1.50. Refrigerators and freezers cycle their compressors more often when the kitchen is warm, which can lift baseline load by 10 to 20% across the appliance fleet for the duration of the heatwave.
Why the bill rises faster than the temperature
Air conditioner efficiency falls as outdoor temperature rises, because the compressor works harder to dump heat into hotter outside air. This means the same 1.5 kW unit delivering the same cooling effect uses more electricity per hour on a 32C day than on a 28C day. The bill therefore rises faster than the linear temperature increase suggests. The same effect, in reverse, applies to gas boilers and outdoor temperatures in winter.
Targeted measures that cut consumption fastest
First, prioritise fans over air conditioning where comfort allows. The energy gap between a fan and a portable AC unit is roughly 20 to 1 per hour. Second, close blinds and curtains on south and west facing windows before the sun reaches them, not after. The reduction in solar gain can cut cooling load by a third. Third, check fridge and freezer door seals and avoid placing hot food directly into either. Fourth, where AC is used, set the thermostat to 24C or above rather than to a target below ambient outdoor temperature.
Where switching tariffs helps and where it does not
For a short duration heatwave, tariff switching is unlikely to save more than the targeted measures above. For households on the default tariff cap, fixed deals that beat the cap have been thin during recent volatility, and exit fees on existing fixes can wipe out the saving. For households on prepayment meters, the cap level was equalised with credit meters from July 2023 onwards, so the structural penalty has gone, but the daily standing charge still applies whether or not electricity is used.
Important
This article gives general information on UK household electricity use during heatwaves. Specific savings depend on tariff, appliance fleet and consumption pattern. Households facing acute affordability stress on bills should contact their supplier and may be eligible for the Household Support Fund administered by their local council, or for the Warm Home Discount in winter.
Common questions
Does the energy price cap rise during a heatwave?
No. The Ofgem default tariff cap is set quarterly and reflects a wholesale reference window. Weather does not change the cap directly. What rises is the household's unit consumption.
Is portable air conditioning more efficient than a fixed split system?
No. Fixed split systems are typically significantly more efficient because they vent heat outside and have larger heat exchangers. Portable units lose efficiency to the warm air they pull from the room through their exhaust hose.
Can I claim help with summer bills?
Schemes such as the Warm Home Discount apply in winter rather than summer. The Household Support Fund, administered by local councils, can be used flexibly for fuel poverty support and may apply. Eligibility varies by council.
