Cooling a bedroom: sleep, quiet running and the right size of unit

How warm is too warm for sleep?

About 26°C is the bedroom benchmark used in the government's 2019 study of overheating in new-build homes. The report itself notes that the figure goes back to a 1975 pilot study of just 21 volunteers, so treat it as a convention rather than a precise line. That report also records that over half of households sometimes meet obstacles to opening their windows, chiefly security and noise: think of a ground-floor flat, or a bedroom above a busy road. Source: MHCLG.

How hot did summer 2026 get?

Hot enough to be provisionally the UK's warmest summer on record. The Met Office gives a mean temperature of 16.5°C, ahead of 16.1°C in 2025, and a peak of 38.2°C at Hartpury College on 13 August, a figure it revised on 17 September after data came in from a manual station. Nearer home, Greenwich, about six miles from Ilford, is the nearest station we found with published Met Office averages; for 1991 to 2020 it shows July days averaging 23.75°C at their warmest and nights about 13.9°C at their coolest. A bedroom that has had sun all afternoon can stay well above the evening air; rooms under the roof have their own guide. Sources: Met Office; Met Office, Greenwich.

Will an air conditioner keep me awake?

Not on its low settings. The three 2.5 kW indoor units in our noise guide drop to 19 or 20 dB(A) on their quietest fan setting and reach 40 to 42 dB(A) only at full speed. Two things decide which end you hear at night: whether the unit is big enough to hold the room on a low speed, and where the outdoor unit sits relative to your window and your neighbours'. If the model has a night setting, ask what it changes. The noise guide has the full figures. Sources: Mitsubishi Electric; Daikin; Fujitsu.

What size of unit does a bedroom need?

Generally 1.5 to 2.5 kW. On iHeat's figures, for standard ceiling heights, 1.5 to 2.0 kW suits 10 to 15 square metres of floor and 2.0 to 2.5 kW suits 15 to 25, with more for big windows or a room under the roof. Glow Green's table runs higher, putting a 9,000 BTU unit in rooms from 14 up to 23 square metres; that is about 2.6 kW using its own conversion of 3,412 BTU per kilowatt. Fujitsu's ASYG KMCC wall range starts at 2.0 kW, and 2.5 kW is the size of all three models quoted on this page. The sizing guide covers the adjustments. Sources: iHeat; Glow Green; Fujitsu.

What does a night of cooling cost?

About £1 to £1.35 at most, on our sums. Even working flat out at its rated input for eight hours, a 2.5 kW unit would use about 3.9 kWh (the Mitsubishi) to 5.0 kWh (the Fujitsu): roughly £1.02 to £1.33 with electricity at 26.32p a kWh, the current cap. Keeping an already cool bedroom cool overnight should need well under full output, so expect less. The running costs guide shows the working. Sources: Mitsubishi Electric; Fujitsu; Ofgem.

Where should the two units go?

The indoor unit high on a wall, aimed so the air runs along the ceiling rather than straight at the bed, with a route for the pipes and drain to an outside wall. The outdoor unit where it disturbs nobody's sleep: away from your bedroom window and your neighbour's, which also helps it pass the 37 dB(A) test. Terraces make up 32.27% of Redbridge homes, and on a terrace that usually points to the back wall or the side return. For how we fit bedroom units across the borough, see air conditioning in Ilford. Sources: Grant UK; Area Insights.