Guide · Heatwave safety

How to keep cool in a UK heatwave — NHS and UKHSA guidance.

A practical, fact-checked summary of what to do when the mercury climbs, drawn from NHS 'Beat the Heat', UKHSA Heat-Health Alerts and CIBSE overheating criteria.

Glass of iced water on a wooden table with drawn window blinds and a pedestal fan in the background
In short

Stay out of the sun 11am–3pm, drink water before you feel thirsty, keep sun-facing curtains closed by day and windows open overnight, and check on older neighbours daily. If someone is confused, has hot dry skin or a temperature ≥ 40 °C, call 999 — that is heatstroke.

Do these first

Four steps that carry the most weight.

  • Stay out of direct sun 11am–3pm

    This is the hottest part of the UK day. If you must be outside, seek shade, wear a wide-brim hat, apply factor 30+ sun cream and slow your pace. NHS and UKHSA guidance both single out this window as the highest-risk period.

  • Drink water regularly, before you feel thirsty

    Thirst lags dehydration by around an hour. Sip water through the day; avoid excess alcohol and very sugary drinks, which pull water out of your cells. Older adults and young children are especially prone to under-drinking.

  • Keep your home cool

    Close curtains and blinds on sun-facing windows during the day. Open windows overnight when outside air is cooler. Move to the coolest room — usually a north-facing ground-floor room — to sleep.

  • Check on people at higher risk

    The NHS lists older adults, babies and young children, people with heart/lung/kidney conditions, and people taking certain medications as higher-risk. A daily phone call during hot spells matters.

Warning signs

Know the line between heat exhaustion and heatstroke.

  • Heat exhaustion (act within 30 minutes)

    Tiredness, dizziness, headache, feeling sick, heavy sweating, cramps, fast breathing or pulse, temperature 38 °C or above. Move to a cool place, remove excess clothing, drink water or a sports drink, and cool the skin with wet cloths or a fan.

  • Heatstroke (call 999)

    Signs include confusion, loss of coordination, seizures, loss of consciousness, hot dry skin, or a temperature of 40 °C or above. This is a medical emergency — call 999 while continuing to cool the person.

Heatwave FAQs

What people ask most during a UK hot spell.

What is the safest indoor temperature during a UK heatwave?
UKHSA and NHS guidance recommend keeping indoor rooms — especially bedrooms — below 26 °C where possible. Above 26 °C sleep quality drops sharply, and above 30 °C the risk of heat-related illness rises for older adults and people with long-term conditions. CIBSE TM52 uses 25 °C as the operative benchmark for non-domestic occupied spaces.
Does closing curtains actually help?
Yes — closing curtains, blinds or shutters on sun-facing windows during the day is one of the highest-impact interventions in NHS and UKHSA 'Beat the Heat' guidance. External shutters or light-coloured reflective blinds block solar gain before it enters the room; internal curtains are less effective but still meaningful.
Should I open windows during a heatwave?
Open windows overnight and in the early morning when outside air is cooler than inside. Keep them closed during the hottest part of the day if outside air is warmer than inside — otherwise you're pulling heat in. Cross-ventilation between two open windows on opposite sides of a room is far more effective than one.
How much water should I drink in a heatwave?
The NHS advises drinking regularly through the day, before you feel thirsty. There is no single UK litre target — the Eatwell Guide suggests 6–8 cups (roughly 1.2 litres) as a baseline, and heat and physical activity raise that. Water, lower-fat milk and sugar-free drinks all count.
Is it dangerous to exercise in a UK heatwave?
Vigorous exercise between 11am and 3pm during an amber or red Heat-Health Alert period materially raises the risk of heat exhaustion and heatstroke. Move workouts to early morning or late evening, cut duration and intensity, and stop immediately if you feel dizzy, sick or confused.
References

Sources for every claim on this page.

Related reading: heat exhaustion & heatstroke first aid, cool an office without AC, AC vs fans in a heatwave, employer heat guidance.

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