The secret to a cool flat in a heatwave is daytime discipline: everything you do between sunrise and evening either keeps heat out or lets it in. Get the day right and you'll coast into a comfortable evening. Here's the routine.
Shade before the sun hits
Sunlight through glass is the biggest source of indoor heat, so block it before it lands. Shade south- and west-facing windows from outside — roller shutters, external blinds, or awnings — ahead of the sun reaching each side. East rooms heat in the morning, west rooms in the afternoon, so pre-empt the sun's path. Outdoor shading beats indoor curtains, but closed light-coloured or thermal curtains help if that's all you have.
Keep windows and doors closed
This is the counterintuitive part: during the hot day, keep windows shut. When it's hotter outside than in, an open window lets hot air pour in and your banked cool air escape. Treat your flat as a sealed cool box during daylight, opening up only at night. Close interior doors too, to contain the cool in the rooms you use and seal off the sunny side.
Switch off heat sources
Appliances quietly heat your home. The oven is the worst offender — cook with the stovetop, microwave, or cold meals on hot days. Turn off lights you don't need, unplug or switch off idle electronics, and avoid running the dryer. Every heat source you eliminate is heat your shading and ventilation don't have to fight.
Bank the cool overnight, trap it by day
Daytime cooling and night ventilation work as a pair: you flush heat and bank cool air overnight (see our Stoßlüften guide), then trap that cool by sealing and shading through the day. The two halves only work together — great night ventilation is wasted if you throw the windows open at noon, and daytime sealing does little if you never ventilate.
Concentrate on the room you use
You don't need every room cool. Focus your shading and sealing on the room you'll spend the day in, and keep it closed off from hotter parts of the flat. A single cool room to work or relax in is a realistic, achievable goal even in a serious heatwave.
When sealing isn't enough
If your flat still climbs despite good daytime habits — a top-floor or very sunny flat — add active cooling. A fan makes a sealed room feel cooler, an air cooler helps in dry heat, and a mobile AC cools a closed room properly. The better you seal and shade, the easier any of these can keep up.
The takeaway
Keep your apartment cool by day: shade before the sun, seal windows and doors, kill heat sources, and ventilate only at night. Master the daytime routine and evenings take care of themselves. Check what's in stock near you if you want to add cooling on top.