A homeowner's guide to air conditioning in UK houses and flats: whether it is worth having, which system suits which property, how to estimate running costs and how to get the most comfort from every kilowatt-hour.
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Not so long ago, air conditioning in a British home was seen as a luxury, or as something you'd only want for a week or two each summer. That's changed. Hot spells come round more often and homes are better insulated and more airtight than they used to be. Lots of people now work all day from a spare room that was never meant to be lived in like that. And the split systems fitted today are reverse-cycle heat pumps, so they heat as well as cool.
This guide looks at domestic air conditioning from the homeowner's side. We cover whether it makes sense for your home and which type of system suits which kind of property, then what it costs to run and how to use it efficiently.
For a lot of households, yes, especially if one or two rooms regularly overheat. Rooms under the roof, south and west-facing rooms with big windows, conservatories, garden rooms and well-insulated new builds can all stay uncomfortably warm in summer, often well into the night. A fan just moves warm air around. It doesn't take out heat or humidity, and an air conditioner does both.
Add heating into the picture and it looks even better value. Run as a heat pump in spring, autumn and winter, a split system can warm a room the central heating struggles to reach, like a loft conversion, an extension or an outbuilding. In plenty of homes it ends up doing more heating than cooling.
It's less likely to be worth it if your home stays comfortable in summer anyway, or you'd only use it a few days a year. Sometimes shading, blinds or better ventilation would fix the room more cheaply. A survey should give you an honest view either way.
A split system moves heat. It doesn't make cold. Refrigerant circulates between the indoor and outdoor units through insulated copper pipes. In cooling mode it soaks up heat from the room air as that air passes over the indoor coil, carries it outside and lets it go through the outdoor unit. Moisture in the room air condenses on the cold coil and drains away, which is why an air conditioned room feels fresher as well as cooler.
In heating mode it all runs the other way. The outdoor unit pulls heat out of the outside air, even on cold days, and the indoor unit releases it into the room. Because it's moving heat around instead of generating it directly, it typically delivers several units of heat for each unit of electricity used.
The building matters as much as the room. The table below shows the combinations we come across most in UK homes.
| Property situation | System that usually fits | Why |
|---|---|---|
| One room that overheats | Single wall-mounted split | Simplest, quickest and least disruptive option |
| Two to four bedrooms or rooms | Multi-split | One outdoor unit serves several independently controlled rooms |
| Flat with limited outside wall space | Compact split or multi-split | Keeps the number of external units to a minimum |
| Extension, new build or loft conversion | Ducted unit | Can be hidden in ceiling voids while the build is open |
| Large open-plan kitchen or living space | Ceiling cassette or larger split | Spreads air evenly across a wide area |
| Conservatory or garden room | Wall-mounted or floor-standing split | Handles heavy summer heat gain and provides winter heating |
For a closer look at the most common options, see our guides to wall-mounted units and multi-split systems. People sometimes look at portable units as a cheaper option. They're noisier, though, they need a hose out of a window, and they use far more electricity for the cooling you get.
Domestic splits are rated in kilowatts of cooling, typically 2.0, 2.5, 3.5, 5.0 or 7.0kW. Room size is only part of the sum. Window area, orientation, insulation and how you use the room all count. Our article on choosing the right unit size explains how it is worked out.
What it costs to run comes down to how much electricity the unit draws (its input power in kW, which is different from its cooling output), how many hours it's on and what you pay per kilowatt-hour. The sum looks like this:
Input power (kW) × hours of use × unit price (p/kWh) = running cost in pence
Say a bedroom unit averages 0.6kW of electrical input while it runs, it's on for 6 hours and electricity costs 25p per kWh. That gives 0.6 × 6 × 25 = 90p for the day. The 25p rate is only an illustration. Check the unit rate on your own electricity bill or tariff and use that figure.
In practice the input power moves around. An inverter unit ramps down once the room is up to temperature, so its average draw is often well under the maximum on the specification sheet. Our full guide to air conditioning running costs covers the factors in more detail.
The way you use a system affects running costs as much as the system you buy. These are the habits the engineers at UK Aircon find make the biggest difference.
On low fan speed a modern indoor unit is quiet, and most have a night or sleep mode that turns the fan down and eases the temperature gradually through the night. Where the unit goes makes a big difference. Air shouldn't blow straight across the bed, and we plan for that on every domestic air conditioning installation.
Air conditioning takes moisture out as it cools, which you'll appreciate on close, humid nights. Some people find the air feels dry if the unit runs hard for hours on end. Moderate setpoints and steady running usually stop that happening.
The filters in an indoor unit catch dust and fibres from the recirculated air, so keeping them clean helps the room stay fresher. Some models add extra filtration stages. If air quality is a particular worry in your home, look at indoor air purifiers and at ventilation alongside air conditioning.
Leaseholders usually need the freeholder's consent before fixing an outdoor unit to the building. Listed buildings, conservation areas and front elevations can need planning or listed building consent, so mention it early. UK Aircon checks with the local planning authority where it applies.
The easiest time to put air conditioning in is while the house is already being altered. During an extension, loft conversion or big refurbishment the ceilings and floors are open. Refrigerant pipes, cables and condensate drains can all go out of sight, and a ducted unit becomes a realistic alternative to a wall-mounted one. If the outdoor unit position is planned with the architect's drawings, it won't end up wherever there happens to be a gap at the end.
Not ready for the full system yet? It can still be worth running the pipework and drainage routes during the build, so the units can go in later with very little disruption. Get the installer involved early, before plastering and decorating, so the routes, electrical supplies and access for servicing are agreed with the builder.
A domestic system needs very little day-to-day attention. Clean the filters every few weeks when it's in heavy use, keep the outdoor unit clear and book a professional service once a year. Do that and it stays efficient and quiet, and you'll have what you need if you ever make a warranty claim. Our guide to air conditioning maintenance covers it step by step.
Yes. Most modern split systems are reverse-cycle air-to-air heat pumps, so they heat as well as cool. They work well for individual rooms, extensions, loft conversions and garden rooms, typically delivering several units of heat for each unit of electricity used.
It depends on the unit's input power, how long it runs and your electricity price. Multiply input power in kW by hours of use and your unit rate in p/kWh to estimate the cost. Inverter units running steadily at low output are usually economical.
Air conditioning removes moisture as it cools, which helps on humid days. Very low setpoints and long periods of hard running can make the air feel dry, so moderate temperatures and steady operation are recommended.
Usually, yes, but you normally need written consent from the freeholder or managing agent to fit an outdoor unit, and the building may restrict where it can go. Compact splits and multi-splits help keep external units to a minimum.
Modern wall-mounted indoor units are quiet on low fan speed and most have a night mode. The outdoor unit is louder, so it should be positioned away from bedroom windows and neighbours where possible and fitted on anti-vibration mounts.
UK Aircon designs and fits home systems from £1,800 installed, sized for the room and backed by a 5-year warranty. Find out more on our domestic air conditioning installation page, or request a free quote and we will reply within 24 hours.
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