How to keep your house cool in summer

The quickest way to keep your house cool is to stop the heat getting in before you try to remove it. Keep curtains and blinds closed on the sunny side during the day, shut windows while it is hotter outside than in, and only ventilate when the air outdoors is cooler, usually overnight and early morning. These free steps do more than any gadget, because UK homes are built to hold heat in, not let it out.

If that is not enough, you can climb a simple ladder of cooling options: free and behavioural fixes first, then a fan, then a portable air conditioner, and finally a fitted split system as the permanent fix. Each rung costs more to buy and run than the last, and each does a bit more. This guide walks through them in order, honest about what each one will and will not achieve, so you can stop at the rung that solves your problem.

Why UK homes get so hot in summer

Most British housing is designed to keep warmth in through long, cold winters, and very few homes have any cooling. That same insulation and heat retention works against you in a heatwave, so rooms warm up through the day and struggle to cool down at night.

The weather is not helping. Summer 2025 was the UK's warmest on record by mean temperature, with four separate heatwaves, and the all-time UK record of 40.3°C was set at Coningsby in Lincolnshire in July 2022, the first time the country passed 40°C. Hot summers are becoming more common, which is why this advice matters more each year.

Some rooms suffer more than others. Heat rises, so upstairs rooms and top-floor flats overheat most. Homes with windows on only one side, large unshaded windows facing east, west or south, or in dense urban areas also run hotter. Even highly insulated, energy-efficient homes can trap heat, so good summer ventilation matters whatever your home is like.

A realistic goal helps too. Cooling a whole UK home for free is hard, so aim to create one cool room: shaded, windows shut by day, doors closed, ideally the room you sleep in. That is far more achievable than trying to cool everywhere at once.

Free ways to keep your house cool

These cost nothing or very little and should always come first. It is easier to stop heat entering your home than to remove it once it is in.

Shade your windows. Close curtains and blinds on the sunny side of the house during the day. External shutters or awnings work even better because they block the heat before it reaches the glass. Solar window film is a cheap-to-moderate semi-permanent upgrade that cuts solar gain, best fitted to your south-facing and sunniest windows first.

Time your ventilation. Open windows only help when the air outside is cooler than inside, which usually means at night and early in the morning. Opening windows while it is hotter outside simply lets heat in and makes the problem worse. Shut them again once the outside air starts to warm up.

Cut indoor heat sources. Turn off and unplug appliances and lights you are not using, check the heating is fully off, and avoid the oven and hob during the hottest part of the day. Cooking at cooler times, or eating cold meals, keeps a surprising amount of heat out of the kitchen.

Make a cool room. Pick one room, keep it shaded with the windows shut by day, close the door, and reserve it for sleeping or resting. Concentrating your effort on one space gives a much better result than spreading it thin.

Do fans actually cool a room?

No. A fan does not lower the air temperature in a room. It moves air across your skin, which helps sweat evaporate and cools your body. That is a real and useful effect, but it only works when someone is in the airflow, so a fan left running in an empty room does nothing except use electricity.

Fans are still the cheapest cooling appliance to buy and to run, which makes them the sensible next rung after the free steps. Position one so the breeze reaches you, and consider a ceiling fan to keep air moving around a room.

The 35°C fan rule

UK official advice from the NHS, UKHSA and the British Red Cross is to use electric fans only when the air temperature is below 35°C. Above that, a fan can blow air that is hotter than your body around the room, adding heat rather than removing it, and can speed up dehydration.

The science is debated. A 2024 review in The Lancet Planetary Health argues the picture is more nuanced, suggesting fans may still help some healthy adults above 35°C while raising the risk for others, such as older people on certain medications. Treat 35°C as the established official threshold, but be aware it is not a settled rule of physics.

A couple of practical points: do not aim a fan directly at your body for long stretches, as that can contribute to dehydration, and remember a fan is cooling you, not the room, so turn it off when you leave.

What about evaporative coolers?

Evaporative air coolers sit between a fan and an air conditioner. They use a fan to move air over water, and the evaporation cools the nearby air slightly. They use far less energy than a portable air conditioner, but they add moisture to the room, so you need to keep it ventilated. They work best in small spaces and in drier air, and they will not transform a hot, humid room.

Are portable air conditioners worth it?

A portable air conditioner is the first option on the ladder that actually lowers the air temperature. It vents hot air out of the room through a hose fitted to a window, so the window seal around the exhaust must be tight or warm air simply leaks back in. They are effective for a single very hot room, but they are noisier, less efficient and far more expensive to run than a fan.

Sizing matters. As a rough guide, around 7,000 BTU suits rooms up to about 16 m sq, 9,000 BTU covers roughly 16 to 26 m sq, 12,000 BTU around 20 to 30 m sq, and 14,000 BTU and up for larger rooms. Treat this as a starting point rather than a promise, and check the maker's own sizing for the model you are considering. Our portable air conditioner buyer's guide goes into sizing and shortlists in more detail.

On price, expect bands rather than fixed figures, and remember stock sells out fast in a heatwave, so buy before a hot spell rather than during one.

These price bands come largely from a single retailer source and date fast; correct at July 2026, so treat them as indicative and check the retailer for current prices before buying.

What is the cheapest way to stay cool?

Free shading and night ventilation aside, a fan is by far the cheapest cooling appliance to run, and a portable air conditioner the most expensive. The table below shows typical GB running costs over 24 hours of use, from the Energy Saving Trust.

Running a portable air conditioner costs up to roughly 20 times more than running a fan.

Independent retailer estimates put portable AC running costs at roughly 21p to 37p an hour, or about £50 to £88 a month at around eight hours of use a day, broadly in line with the figures above.

Here is the maths behind a worked example. The Ofgem price cap unit rate for electricity on a standard variable tariff paying by Direct Debit is 26.11 pence per kWh (the average across England, Scotland and Wales, including VAT at 5%) for 1 July to 30 September 2026. A typical 9,000 BTU portable unit draws around 1 kW, so running it for eight hours uses about 8 kWh: 8 x £0.2611 = roughly £2.09 a day, or about £63 a month. A 50 W pedestal fan run for the same eight hours uses 0.4 kWh, costing about 1p a day. That gap is why fans win on cost every time, and why air conditioning is a comfort decision as much as a cooling one.

Prices and rates correct as of July 2026. The energy price cap changes quarterly, so check current rates before budgeting.

Fan or air conditioning: which should you use?

For most UK homes most of the time, a fan plus good shading and night ventilation is enough, and it costs a fraction as much to run. Reach for cooling that lowers the air temperature, a portable unit or a fitted system, when a single room is genuinely uncomfortable, when someone in the household is vulnerable to heat, or when you simply want reliable comfort through every hot spell.

If you find yourself buying and running a portable unit summer after summer, a fitted system often makes more sense in the long run. It is quieter, more efficient and a permanent solution, and it adds the structure that a portable cannot.

The permanent fix: a fitted split system

A fitted split system is the top of the ladder. It pairs an indoor wall unit with an outdoor condenser, professionally installed, and cools effectively and quietly. Choose a reverse-cycle model, an air-to-air heat pump, and the same unit will also heat your home in winter. Reverse cycle simply means it can run in both directions, taking heat out of the room in summer and pumping heat in during winter. These units are common across Europe and increasingly popular in the UK as summers warm.

A few things are worth knowing before you commit:

• A split or reverse-cycle system contains fluorinated refrigerant, known as F-Gas, so it must be installed by an F-Gas certified engineer. A DIY install is effectively off the table.

• The outdoor condenser raises planning rules. A cooling-only unit is generally not covered by permitted development in England and usually needs full planning permission. The permitted-development right applies only to reverse-cycle units that also heat, and even then subject to conditions on size, siting and noise. Scotland, Wales and Northern Ireland differ, so always check your local planning authority.

• Installation usually involves notifiable electrical work under Building Regulations.

• On grants, do not expect free air conditioning. A £2,500 grant for air-to-air heat pumps came into effect on 28 April 2026 in England and Wales, but it is tightly conditioned: the unit must heat as well as cool, replace an existing fossil-fuel or electric heating system and be fitted by an MCS-certified installer. It does not cover comfort-only cooling alongside a retained gas boiler, and it does not cover portable units. The larger £7,500 Boiler Upgrade Scheme grant is for air-to-water heat pumps, which are a different product.

Costs vary widely with capacity and how complex the install is, so a supplied-and-fitted single split is best treated as a band rather than a single figure. For current ranges, see our air conditioning cost guide, and when you are ready, compare quotes from local F-Gas registered installers to budget accurately. You can also browse wall-mounted split systems to see typical options.

How hard you have to work at this depends partly on where you live. The Air Con Index ranks the 91 towns and cities in England and Wales with the strongest case for home cooling, scored on summer heat, housing type and affordability.