Is bedroom air conditioning worth the money?

What temperature is too hot to sleep?

The standard for new homes in England, CIBSE TM59, says a bedroom should not go above 26°C between 10pm and 7am for more than 1% of the hours in the year. Government researchers noted in 2019 that the figure traces back to a pilot study of 21 volunteers in 1975, so treat it as a working line rather than a medical one. The same report estimated that overheating can cut a good night's sleep from eight hours to six or seven. Source: MHCLG research.

How warm do Croydon nights actually get?

Warmer than the averages. On the night of 18 July 2022 the Met Office station at Kenley Airfield, in the south of this borough, recorded a minimum of 25.8°C, which stood as the UK's warmest night on record until a reading of 26.8°C from Oxfordshire was confirmed. Inside a top-floor bedroom under a hot roof, the air is warmer than the air at the airfield, and it stays that way after the sun has gone. Source: Met Office.

What should you try first?

• Close the blinds or curtains on the sunny side during the day, not just at night.
• Open windows at night where that is safe and quiet enough, and open one on each side of the home if you can.
• Run a fan across the bed.
• Sleep in a cooler room on the worst nights.

In a UCL study of converted lofts, night ventilation cut overheating by 89% and was the most cost-effective measure. The government research explains why many people cannot use it: over half of households sometimes feel unable to open windows, mainly for security or noise, and on a main road or a ground floor that is a daily reality. Sources: Li, Taylor and Symonds; MHCLG research.

Fixed or portable for a bedroom?

The prices are Checkatrade's national figures for 12,000 BTU units, with the fixed figure being its unit and labour prices added together. If you own your home and sleep lightly, fixed is the better long-term buy. If you rent, a portable is usually the honest answer, and a monobloc sits between the two. Source: Checkatrade cost guide.

What size does a bedroom need?

iHeat gives 1.5 to 2.0kW for 10 to 15 square metres and 2.0 to 2.5kW for 15 to 25, with more for a room under the roof, a west-facing window or a lot of glass. Going far too big is a mistake as well, because an oversized unit cools the room quickly, switches off, and leaves the air clammy. The size guide explains the adjustments. Source: iHeat.

Will it keep you awake?

Not if it is chosen and placed with sleep in mind. Pick a model with a low fan setting and check its quoted sound level at that speed. Mount it so the airflow crosses the room rather than landing on the bed. Think about the neighbours as well. Permitted development hinges on a calculated 37 dB(A) or lower beside their nearest door or window, and in a Croydon terrace the bedrooms are often two metres apart across the fence. Source: Grant UK.

What does a night cost?

On Checkatrade's 20p to 60p an hour, eight hours is £1.60 to £4.80. A modern unit holding a steady temperature should sit at the bottom of that range or below it. Using the Energy Saving Trust's typical cooling efficiency of around 7, a 2kW unit draws about 0.29kW, which at the current 26.32p cap is about 7.5p an hour, or 60p for the night. Sources: Checkatrade cost guide; Energy Saving Trust; Ofgem.