Quick answer: heatwaves, UK homes and the cooling cost in 2026
- First UK 40°C reading
- 40.3°C
- Coningsby, 19 July 2022
- Climate change effect
- ~10x
- More likely than pre-industrial
- UK homes with no AC
- ~95%
- Built for cold, not heat
- Fan vs AC weekly gap
- £15+
- Same hours, same week
- Ofgem electricity cap
- 24.67p
- per kWh, 1 April to 30 June 2026
Heatwaves are now a UK problem, not a holiday memory
For most people who grew up here, 30°C was a "good summer". Anything higher meant a flight south. That picture has changed. On 19 July 2022 the Met Office recorded 40.3°C at Coningsby in Lincolnshire, the first time a UK weather station has ever crossed 40°C. The previous all-time record, 38.7°C set in Cambridge in 2019, was broken by more than 1.5°C in a single afternoon.
That is not a one-off statistical wobble. The Met Office and the World Weather Attribution group estimate that climate change has made a 40°C event in the UK roughly ten times more likely than it would have been in a pre-industrial climate. The pattern since 2018 (long, dry, hot summers in 2018, 2019, 2020, 2022 and 2025) is what climate scientists were modelling for the 2050s only a decade ago.
The financial side of this story usually gets ignored. Heat is electric in the UK: no gas boiler heats your home in August, so every extra fan, every portable AC, every fridge working harder against a warm kitchen, runs straight off your electricity meter. The Ofgem price cap, currently set at 24.67p per kWh for the 1 April to 30 June 2026 period, is the speed limit for what those extras cost.
Definition. A kWh (kilowatt-hour) is one unit of energy: the amount a 1,000-watt appliance uses in one hour. A 50-watt desk fan uses 1 kWh in 20 hours; a 1,500-watt portable AC uses the same kWh in 40 minutes. The standing charge is a flat daily fee for being connected to the grid; on electricity it is currently 57.21p per day at the cap.
Why most heatwave advice misses the point
Open any "heatwave tips" article and you will find the same five lines: close the curtains, drink water, take cool showers, wear loose clothing, check on older neighbours. All of that is necessary. None of it tells you what your home is doing wrong, or what it is costing you.
The expert reading of a UK heatwave is different. In a country where 95% of homes have no AC, the single biggest cooling lever is not what you turn on, it is what you stop the heat from getting at: window shading, ventilation timing, appliance choice, and the surprising amount of heat that comes from inside the house (fridges, set-top boxes, tumble dryers, ovens) rather than through the windows. These are the levers that work even when the temperature is above what your home was designed for.
The cost side of this matters too. A pedestal fan running 24 hours a day for a full week of heat costs roughly £3 at the Q2 2026 Ofgem price cap, about the same as a coffee. A portable AC running 8 hours a day for the same week costs around £20, the price of a takeaway dinner for two. Use both badly and a hot week can add £40 to your electricity bill before you have made a single cup of tea.
Why your UK home overheats
UK building regulations were written for one problem: keeping heat in during winter. Almost everything that helps you in January (thick walls, small windows, low ceilings, heavy insulation) traps heat in July. There are four specific reasons your home struggles when the temperature climbs.
An envelope built for cold
UK homes are sealed and insulated to stop heat escaping. In summer that same envelope works in reverse: once warm air is inside, the insulation that kept it out of January now keeps it in until October. A well-insulated 1960s semi can sit at 27°C indoors when the outside is 22°C and falling overnight, because the heat has nowhere to go.
Glazing that lets the sun cook the room
Modern UK extensions and new-builds use a lot of glass. South or west-facing single-pane glass, or even older double glazing without a solar control coating, can let in over 600 watts of solar gain per square metre of window. A 4 square metre patio door facing west can add up to 2.4 kW of heat to a room in late afternoon, equivalent to leaving a 2.4 kW fan-heater running.
No shutters, no external shading
Walk down a residential street in southern Europe in summer and most windows have external shutters or external blinds. In the UK, almost none do. External shading stops the sun before it hits the glass. Internal curtains and blinds (the UK default) only block the light after it has already entered the room and warmed the air, so they help less than half as much.
Appliances that quietly heat the room
Every watt of electricity an appliance uses ends up as heat inside the room. A tumble dryer adds about 2 kW for an hour. An oven on at 200°C adds roughly 1.5 kW for the duration. A 4K TV adds 150 W; a games console under the TV adds another 100 W; a desktop PC under the desk adds 200 W. By dinner time, a home office with the lights, screens and a tumble dryer drying a load of towels has put about 3 kW of heat into the house, more than a single-bar electric fire on full.
The "envelope and load" rule. If you only do one thing this summer, treat your home as a sealed box. Stop heat getting in (windows, blinds, ventilation timing) and stop heat being made inside (appliance use during the day). Cooling with fans or AC only matters after those two are sorted.
Cooling that works vs cooling that wastes money
There is a simple test for any cooling option: does it cool you, or does it cool the room? A fan does the first; an air-conditioner does the second. Fans are cheap to run because they only move air; air-conditioners are expensive to run because they actually pump heat out of the room and dump it outside.
A fan moves air across your skin to help sweat evaporate faster, which is how your body cools. It uses 50 to 80 watts of electricity. An AC compressor extracts heat from inside air and rejects it outside; it uses 700 to 1,500 watts to do the job. That is why a fan and an AC running the same hours can be a 10 to 20 times difference in cost on your bill.
The cheap structural fixes that beat both
Before you spend on either, do the things that cost almost nothing and run for free:
- Close windows, curtains and blinds on south and west-facing rooms by 7am;
- Use light-coloured or foil-backed curtains, or stick reflective film on the inside of the worst windows;
- Open windows on opposite sides of the home after 9pm to push the day's heat out;
- Stop using the tumble dryer (hang washing outside) and the oven (cook on the hob or eat cold) during the hot hours;
- Check the fridge door seal: a leaking seal makes the compressor run twice as hard and heat the kitchen;
- Switch off chargers, set-top boxes and game consoles at the wall when not in use.
When a fan is enough
For most UK homes, a pedestal or tower fan pointed at the person who needs cooling is enough through the worst hours. The fan does not lower the room temperature, but it can make you feel 3 to 4°C cooler. At 80 W and the cap, running it 8 hours a day for a whole week of heat costs about £1.10.
When AC starts to make sense
Air-conditioning earns its cost in a few specific cases: a south-facing top-floor flat that does not cool overnight, a bedroom shared with a baby or older person who cannot tolerate heat, or a home office where you need to work through a 35°C afternoon. In those cases, cool one room, not the whole house, and for the hours you need it, not all day. The calculator below shows what the difference looks like on your bill.
The heatwave home cooling cost calculator
Pick a cooling option, how long you would run it each day, and how many heat days you expect. The widget converts watts to kWh and prices it at the Q2 2026 Ofgem price cap electricity unit rate of 24.67p per kWh. No submit button, no email capture.
Your cooling plan
What it costs
Total cost at the Ofgem cap
£
kWh used over the period
A , hours a day for days, costs about £ at the Q2 2026 Ofgem price cap. That is almost times the same hours on the cheapest fan in this list. Switching to the priciest AC in this list for the same hours would cost £, about times more.
Fan vs AC, same hours, same days
Gap: £ for the same week of cooling.
Heat-day savings checklist: cheap structural fixes
Twelve specific actions, in the order they pay back fastest. Each one costs little or nothing and reduces what you need to plug in.
-
1
Pre-cool overnight with cross-ventilation.
After 9pm, when outside temperature falls below inside, open windows on opposite walls (front and back of the house) to flush the day's heat out.
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2
Close everything by 7am.
Once the sun is on the glass, every open window is letting hot air in. Shut windows, curtains and blinds on south and west faces before breakfast.
-
3
Use the foil-back curtain trick.
Tape kitchen foil, shiny side out, to the inside of the worst single-pane window. Cheap, ugly, and reduces solar gain by 50 to 70% on that pane.
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4
Time hot appliances around the heat.
Run the dishwasher, washing machine and oven before 8am or after 9pm, never in the heat of the afternoon. A 2 kW dryer on at 3pm is heating your home for free.
-
5
Check the fridge door seal.
A leaking seal makes the compressor work twice as hard, both running up the electricity bill and heating the kitchen. Test with a paper note: if you can pull it out without resistance, the seal is gone.
-
6
Hang washing outside.
A tumble dryer adds about 2 kW of heat into the home for every hour it runs. In a heatwave it is the worst appliance you own.
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7
Cook on the hob, the air-fryer, or eat cold.
An oven on for an hour adds the same heat as a 1.5 kW fan-heater. An air-fryer uses a third of that, in a sealed pot.
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8
Switch off standby and chargers at the wall.
A set-top box, games console and three chargers left plugged in add up to 30 to 60 W of constant heat into a small room, day and night.
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9
Point the fan at people, not at the room.
A fan does not cool air, it moves air across your skin so sweat works harder. Aimed at the empty centre of the room, it does almost nothing.
-
10
Put a damp cloth in front of the fan.
As the air pushes through the damp fabric, it cools through evaporation by 2 to 3°C. Costs nothing on top of the fan running cost.
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11
If you must use AC, cool one room only.
A portable AC in a bedroom for the four hours before sleep costs roughly £1.50 a night at the cap. The same unit cooling the whole house all day costs ten times that.
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12
Shift cooling to the cheap window with a time-of-use tariff.
Economy 7 and other off-peak tariffs price overnight electricity well below the daytime cap. Pre-cool the bedroom between midnight and 5am, then close it up before sunrise.
The adaptation gap. The UK is around 0.5°C past the climate most of its housing was built for. Until building regulations and retrofit grants catch up, the cheapest cooling you have is your own behaviour: shading, timing, appliance choice. A fan, used well, beats a badly used AC every time.
Frequently asked questions
Switch to a tariff that handles heatwaves better
The Ofgem price cap sets the maximum unit rate every supplier on a default tariff can charge during a heatwave, currently 24.67p per kWh. A well-chosen fixed deal or time-of-use tariff can sit below that ceiling, which makes every extra fan-hour or AC-hour cheaper.
Selectra's UK energy team checks tariffs against your real consumption, your region, and your meter type. If you run a fan most evenings, a standard fixed deal usually works. If you pre-cool overnight or have a smart meter, an Economy 7 or EV-friendly off-peak tariff can move much of the cooling cost into the cheap window.
Call our UK advisers on 020 3936 0059 for a 5-minute review of your current tariff against today's cap and the fixed deals on the market.