Most of the time, a hot flat is just uncomfortable. But indoor heat can cross from unpleasant into genuinely risky, especially for vulnerable people — and knowing the line helps you act before it matters. Here's a practical, non-alarmist guide.
When heat becomes a health concern
Your body cools itself by sweating and shedding heat to its surroundings. A room becomes a health concern when it stays hot enough that this becomes hard work, particularly overnight, when you should be recovering from the day's heat. Sustained indoor heat that prevents sleep, leaves you constantly drained, or keeps a vulnerable person uncomfortable is a signal to take cooling seriously rather than tough it out.
Warning signs of heat stress
Learn the signs in yourself and others:
- Dizziness, light-headedness, or headache
- Heavy sweating — or suddenly stopping sweating despite the heat
- A rapid or pounding pulse
- Nausea, muscle cramps, or unusual fatigue
- Confusion or disorientation (a serious sign)
Mild signs mean cool down and hydrate now. Severe signs — confusion, fainting, a very high temperature — need urgent attention; cool the person and seek medical help.
Who's most vulnerable
Some people feel indoor heat far more dangerously than others: babies and young children, the elderly, anyone with a chronic illness or on certain medications, pregnant people, and pets. Their bodies regulate temperature less effectively, so keep their rooms the coolest, check on them frequently during a heatwave, and make sure they drink enough. See our guides on keeping babies cool and keeping pets cool.
How to bring a hot room down fast
If a room is dangerously hot, act on both the room and the body:
- Cool the person first — move them to the coolest room, give cool (not ice-cold) water, apply damp cloths to the neck and wrists, and aim a fan across them.
- Cool the room — close and shade windows against the sun, and once it's cooler outside, ventilate hard to flush heat.
- Add active cooling — an air cooler in dry heat or a mobile AC for a sealed room brings the temperature down faster than passive methods alone.
Don't wait it out for vulnerable people
The key judgement: a healthy adult can usually ride out a hot afternoon, but for a baby, an elderly relative, or a pet, persistent indoor heat is worth acting on early rather than hoping it passes. Prioritise keeping their space cool, and treat warning signs seriously.
The takeaway
"Too hot" is less about a magic number and more about whether bodies can cope and recover, especially overnight and especially for the vulnerable. Watch for heat-stress signs, cool people and rooms promptly, and keep vulnerable household members coolest. If you need to add cooling, check what's in stock near you.
This is general guidance, not medical advice. For serious heat-related symptoms, contact a medical professional or emergency services.