How to Keep a Baby Cool at Night During a UK Heatwave

By Angelica Videla — Certified Baby and Toddler Sleep Consultant, London | Supporting families across the UK, Europe, US, and Australia

Why UK heatwaves hit baby sleep so hard

Most UK homes are built to retain heat, not release it. Unlike homes in warmer climates, the majority of UK houses have thick insulation, double glazing, and no air conditioning. During a heatwave, this means nurseries absorb heat during the day and hold it well into the night. A room that reaches 28°C by mid-afternoon may still be 26°C at midnight.

Babies are more vulnerable to heat than adults because they cannot regulate their body temperature as effectively. They have a higher surface-area-to-weight ratio, they cannot remove their own bedding, and they cannot tell you they are too warm. This is why overheating is a risk factor highlighted by the Lullaby Trust and every safe sleep guideline.

The good news is that a UK heatwave is temporary — typically lasting 3 to 7 days. With the right adjustments, your baby can sleep safely and reasonably well through it. Sleep may be slightly more disrupted than usual, but that is normal and will resolve quickly once temperatures drop.

Room temperature: what the numbers mean

The ideal room temperature for baby sleep is 16 to 20°C. During a heatwave, achieving this without air conditioning is often impossible. Here is how to respond at each level:

20 to 24°C: Warm but manageable. Use a 1.0 TOG sleeping bag with a short-sleeve bodysuit or vest. No additional action needed beyond normal summer precautions.

24 to 27°C: Hot. Switch to a 0.5 TOG sleeping bag or a lightweight muslin sleep sack with just a nappy underneath. Use a fan to circulate air. Keep curtains closed during the day.

27 to 30°C: Very hot. No sleeping bag needed. Your baby can sleep safely in just a nappy. A fan is essential. Consider a damp muslin cloth hung near the fan to cool the air slightly.

Above 30°C: Move your baby to the coolest room in the house, even if that means a temporary change in sleep location. Ground-floor rooms and north-facing rooms are typically the coolest.

What your baby should wear to sleep during a heatwave

Clothing decisions during a heatwave should be based on the actual room temperature at the time you put your baby down — not the forecast, not the outdoor temperature, and not what the room felt like earlier in the day.

24 to 27°C: A breathable summer sleep sack (0.5 TOG or muslin) with a nappy only, or a short-sleeve vest if you prefer a layer. The muslin fabric breathes significantly better than cotton at higher temperatures.

Above 27°C: Just a nappy. No sleeping bag, no vest, no socks. Your baby's skin needs to be exposed to release heat effectively.

If you are unsure, underdress rather than overdress. A slightly cool baby will sleep far better than an overheated one. Check the back of the neck regularly — it should feel warm and dry, never hot or sweaty.

For a complete layer-by-layer guide at every temperature: how to dress a baby for sleep by room temperature. For detailed TOG guidance: what TOG sleeping bag does my baby need?

How to cool the nursery without air conditioning

Close curtains and blinds during the day. This is the single most effective passive cooling measure. Blackout blinds do double duty — they block both light and solar heat gain. Close them from mid-morning and keep them closed until the sun moves off the window.

Use a fan. A fan does not cool the air — it moves it, which helps sweat evaporate from skin and makes the room feel cooler. Point the fan toward a wall or upward toward the ceiling rather than directly at the cot. Position it well out of reach. A fan running all night is safe and significantly improves comfort.

Open windows strategically. During the day, keep windows closed if the outside temperature is higher than the inside temperature. In the evening and overnight, open windows on opposite sides of the house to create a cross-breeze. Always use a window restrictor that limits the opening to no more than 6.5cm.

Try a damp towel or muslin near the fan. Hanging a damp cloth in front of or near the fan creates a rudimentary evaporative cooling effect. This can reduce the perceived temperature by 1 to 2°C.

Move rooms if necessary. If the nursery is on an upper floor or south-facing, it may be significantly hotter than other rooms. Temporarily moving the cot or travel cot to a cooler room is a practical and entirely reasonable response.

Hydration during a heatwave

Under 6 months: Do not give water. Breast milk and formula provide all the hydration your baby needs. Offer extra feeds — your baby may want to feed more frequently during hot weather. Breastfed babies may take shorter, more frequent feeds. This is normal and appropriate.

6 to 12 months: Offer small sips of cooled boiled water between feeds. Continue breast or formula feeds as normal. You can also offer water-rich foods like cucumber, melon, and yoghurt during meal times.

Over 12 months: Offer water regularly throughout the day. A sippy cup of water accessible during wake periods ensures your toddler stays hydrated. Watch for signs of dehydration: fewer wet nappies, dark urine, dry lips, lethargy.

How heat affects naps

Daytime naps are often more affected than nighttime sleep during a heatwave because peak room temperatures typically occur between 2pm and 6pm — exactly when afternoon naps happen.

Expect shorter naps. Naps in a hot room will often be 30 to 45 minutes rather than the usual 60 to 90. This is normal during a heatwave. Do not try to extend the nap — a hot, uncomfortable baby will not resettle.

Consider an earlier morning nap. If your schedule allows, shifting the first nap slightly earlier captures the cooler morning temperatures. The afternoon nap is typically the hardest during a heatwave.

A pram nap in the shade outdoors may actually be cooler than the nursery during peak afternoon heat. Use a breathable sunshade and monitor your baby closely.

How overheating affects sleep quality

Heat disrupts sleep in several specific ways. Understanding these helps explain why your baby's sleep pattern changes during a heatwave — and why it resolves quickly once temperatures drop.

Lighter sleep cycles. The body needs to drop its core temperature slightly to enter deep sleep. When the room is hot, this temperature drop is harder to achieve, which means your baby spends more time in light sleep and less in the restorative deep sleep phases.

More frequent waking between cycles. During light sleep phases, discomfort from heat is more likely to trigger a full waking. This is the same mechanism that causes night waking from any environmental discomfort.

Earlier morning waking. Body temperature naturally rises in the early morning hours. In a hot room, this rise pushes the baby past the comfort threshold earlier, producing a wake-up at 5am instead of 6:30am.

These are all temporary. Once room temperature returns to normal, sleep quality recovers within 1 to 3 nights. For more on why environmental factors drive night waking: night wakings guide. For early morning waking specifically: early morning wakings guide.

Signs of overheating to watch for

• Hot, sweaty, or clammy skin on the back of the neck or chest
• Damp hair
• Flushed or red cheeks
• Rapid breathing
• Restless, unsettled sleep with frequent waking
• Heat rash — small red spots, typically on the neck, chest, or in skin folds
• Irritability and difficulty settling that is unusual for your baby

If you notice these signs, remove a layer, turn on the fan, and offer a feed. If your baby seems lethargic, unresponsive, or has a very high temperature, seek medical advice immediately.

A heatwave checklist for tonight

• Check the nursery thermometer at bedtime — dress your baby for the actual temperature
• Close curtains and blinds well before bedtime to prevent further heat build-up
• Set up a fan aimed at the wall or ceiling, well away from the cot
• Use a 0.5 TOG muslin sleeping bag or just a nappy depending on temperature
• Offer an extra feed before bed to ensure hydration
• Open windows if the outside temperature is cooler than inside (use a restrictor)
• Keep your regular bedtime routine — consistency helps even when conditions are not ideal
• Accept that sleep may be shorter and more broken than usual — this is normal and temporary

After the heatwave

Once temperatures return to normal, switch back to your regular sleeping bag and clothing immediately. Return to your usual bedtime. Most babies readjust within 1 to 3 nights.

If your baby's sleep was already disrupted before the heatwave and does not recover afterwards, the heat may have been masking an underlying schedule or settling issue. A personalised sleep plan can identify what needs to change and in what order.