Best air conditioning options for a bedroom

The short answer

For most UK bedrooms, a high-wall split air conditioner is the best option. It keeps the compressor outside, holds a steady temperature through the night, and heats the room in winter as well. The things to get right are the sound level on the lowest fan speed, the size in kW, where the indoor unit points and where the outdoor unit goes.

A portable unit is the fallback for renters, flats where an outdoor unit isn't allowed, or a spare room used a few nights a year. It is louder, because the compressor is in the room with you, and it needs a window open for its hose. Our guide to fixed versus portable air conditioning compares the two in detail.

If you share a wall with a neighbour, as most terrace and semi owners in Leeds do, the outdoor unit's position needs as much thought as the indoor unit. A quiet bedroom for you shouldn't mean a noisy one for them, and the permitted development rules are built around that.

Noise is the deciding factor

For sleep, sound level matters more than any other figure on the data sheet. The World Health Organization's guidelines for community noise suggest a continuous level of no more than 30 dB(A) inside a bedroom for good sleep. That gives you a benchmark to compare against.

Ask for the indoor unit's minimum sound pressure level in dB(A), on its quietest fan setting, and compare it with the 30 dB(A) figure. Manufacturers publish this on the data sheet. Check how it is measured, since some quote it at 1 metre and others at a different distance, which changes the number.

Decibels are a log scale. An increase of 10 dB is ten times the sound energy and sounds roughly twice as loud, so a unit quoted a few decibels lower can make a difference you will notice at 2am.

The outdoor unit matters as well. Putting it directly under your own bedroom window, or near your neighbour's, is a common mistake. Under permitted development it also has to meet a 37 dB(A) limit at the neighbour's nearest habitable room window, calculated with the MCS 020 a) method. Our noise guide shows the calculation in full.

Getting the size right

Size means cooling capacity in kW, not the physical size of the unit. Daikin's UK sizing guide gives a rule of thumb of about 0.1kW per square metre for a typical UK room with a 2.4m ceiling and average insulation, then adds capacity for higher ceilings, large south or west facing windows and more than two people.

Worked example: a loft bedroom in a Leeds terrace. The room is 4m by 3.5m, so the floor area is 14 square metres. At 0.1kW per square metre, that is 14 x 0.1 = 1.4kW. The room faces south-west with a large dormer window, and Daikin suggests adding 10% to 20% for that. Taking the top of the range, 1.4 x 1.2 = 1.68kW. In BTU, using 1kW = 3,412 BTU per hour, that is about 5,730 BTU per hour. Since domestic split units come in set sizes, the installer would pick the smallest model in the range that covers about 1.7kW. A loft room under a slate roof may need more than the rule suggests, which is why a proper heat-gain calculation at survey beats a rule of thumb.

Oversizing isn't a safe default. An oversized unit cools the air quickly and then shuts off, which leaves the room clammy, because it doesn't run long enough to take moisture out of the air. Our sizing guide covers this in more depth.

Features worth having in a bedroom

These are the features that make the most difference at night.

• A sleep or night mode that lowers fan speed and eases the temperature up gradually.
• Adjustable louvres so cold air isn't blown straight at the bed.
• A timer, so the room is cool before you go to bed.
• An indoor display that can be switched off.
• Good filters, if anyone in the house has allergies.

Where to mount the indoor unit

The usual position is high on a wall, ideally on a wall facing the bed or to one side of it, so the air crosses the room before it reaches you. Mounting it directly above the bed sends cold air straight down onto you. Avoid fitting it above a radiator, where warm air would rise into it, or straight opposite a sunny window.

The indoor unit also needs a route for the refrigerant pipes and condensate drain to the outside. On a back bedroom with the outdoor unit below on the same wall, that route is short. On a front bedroom where the outdoor unit has to go at the back, the pipes may run through a loft or along a landing, which adds work. Ask the installer to explain the route before you agree a position.

In a loft room with no gravity route to a drain, the installer will fit a small condensate pump. Pumps make some noise, so ask where it will sit and whether it can be placed away from the bed.

Comparing models on efficiency

Once you have two or three quotes, compare the efficiency figures as well as the price. Cooling efficiency is given as SEER, the seasonal energy efficiency ratio, and heating efficiency as SCOP, the seasonal coefficient of performance. Daikin's UK guide describes a SEER of 8.5 or more as A+++ on the energy label and 6.1 to 8.5 as A++, and calls a SCOP above 3.5 high performance.

A higher SEER means less electricity for the same cooling, and a higher SCOP means cheaper heat. In a bedroom used mainly on summer nights, SEER and the minimum sound level matter most. In a loft room you also plan to heat from October to April, SCOP matters as much.

Look at the capacity range as well. Inverter units can run below their rated capacity, and a unit that turns down further will run more quietly and more steadily on mild nights. The data sheet gives the minimum and maximum capacity for cooling and heating.

Finally, check the controls. Some people like an app so they can cool the room before they get home. Others prefer a simple remote. Either way, a timer and a sleep mode are the features you will use most.

Leeds bedrooms that overheat

Average summers in Leeds are mild. The Met Office 1991 to 2020 averages for the Leeds Weather Centre station put the mean daily maximum at 21.4°C in July. The bedrooms that cause trouble are the ones that trap heat on top of that.

Leeds City Council counts about 19,500 pre-1919 back-to-back houses in the city. Their attic bedrooms have one outside wall, a roof directly above and no through draught, so they stay warm well into the night. Dormer bedrooms in Victorian terraces in Headingley, Burley and Armley are similar, and so are upstairs rooms in new-build homes with large south-facing windows.

Houses near the Ring Road, the A65 or Leeds Bradford Airport have a second reason to want a unit, since opening the window at night lets in traffic or aircraft noise. A unit lets you keep the window shut.

What it costs to run overnight

At the Ofgem price cap for 1 October to 31 December 2026, electricity averages 26.32p per kWh by Direct Debit. Say the unit averages an assumed 0.6kW for 6 hours. That is 0.6 x 6 = 3.6kWh, and 3.6 x 26.32p = 94.8p a night. Check the rated power input on the data sheet for your model. Our running costs guide has more examples.

Planning, VAT and who can fit it

On most houses in England, the outdoor unit can go up under permitted development if it is 1.5 cubic metres or smaller and meets the 37 dB(A) noise limit. Leeds has 80 conservation areas, where the unit can't go on a wall facing a road under those rules. Flats need the freeholder's consent and listed buildings need listed building consent.

Installing an air-to-air heat pump in a home is zero-rated for VAT until 31 March 2027 under HMRC's VAT Notice 708/6. Our partner installers are MCS certified and apply the 0% rate to domestic installations.

Sources

• World Health Organization, Guidelines for community noise
• Daikin UK, Air conditioner size guide
• MCS 020 a) sound calculation
• Ofgem, Energy price cap unit rates
• Leeds City Council, Leeds Housing Strategy
• Met Office, UK climate averages (1991 to 2020)
• Leeds City Council, Conservation areas
• HMRC, VAT Notice 708/6: energy-saving materials and heating equipment