Bedroom air conditioning: what it does for sleep, and what it costs

What temperature stops you sleeping?

About 26°C, according to the overheating research the government published in 2019, which uses that figure as the bedroom threshold while admitting it rests on a small 1975 pilot study. The same research found that more than half of households sometimes report barriers to opening their windows, mainly noise and security. In Dartford that means a bedroom near the A2, the A282 or the Crossing's approach roads, or a ground-floor flat, where the window stays shut on the hottest nights of the year. Source: MHCLG.

How hot do bedrooms here get?

Hotter than the air outside by evening. Greenwich Observatory, the nearest Met Office climate station, averages a July high of 23.75°C and a July night-time low of 13.9°C, but a top-floor room that has taken the sun all afternoon can stay in the high twenties long after the street has cooled. The summer of 2026 was provisionally the UK's hottest on record, with a mean of 16.5°C and a peak of 38.1°C at Kew on 13 August, and the newest homes, airtight and often single-aspect, hold the heat longest. Sources: Met Office; ITV News; Elmhurst Energy.

How loud is a bedroom unit at night?

Quiet, if you choose for it. The compressor is outside; the indoor unit holds a fan and a coil, and at its lowest speed many models are quieter than a fridge. Ask for the sound figure at the lowest fan setting, not the headline figure, and ask for a model with a sleep mode that raises the set temperature gently through the night. For the neighbours, the outdoor unit must calculate at 37 dB(A) or less beside their nearest window, which is lower than ordinary night-time traffic noise. Source: Grant UK.

What size does a bedroom need?

Less than people expect. iHeat's guide gives 1.5 to 2.0kW for a room of 10 to 15 square metres and 2.0 to 2.5kW for 15 to 25, then more for large or south-facing windows and for a loft conversion. Oversizing is a real fault: a unit that is too big cools the air quickly, switches off before it has dried the room, and cycles on and off all night. The size guide explains the adjustments. Source: iHeat.

What does a bedroom unit cost?

On Checkatrade's national figures for May 2026, £750 for a 12,000 BTU unit and £1,150 to fit it, which we make about £1,900, plus £400 to £700 for the electrics; a bedroom usually needs the smaller end of the range, so the unit may cost less than that. Running it to hold temperature works out at about 9p an hour on the current price cap for a 2.5kW unit. In winter the same unit heats the room for roughly a quarter of what a plug-in heater costs, which is covered on the heat pump page and summarised on our air conditioning in Dartford page. Sources: Checkatrade; Ofgem; Energy Saving Trust.