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Selecting the right type of Air conditioning installation

Types of air conditioner

  • Split-system: These have two parts: an outdoor compressor unit and an indoor unit connected by pipes. They’re usually used to cool one or more rooms, or an open-plan area, of up to 60 square meters. Price range: £600-£5000
  • Multi-split: A type of split-system, with one outdoor unit connected to two or more indoor units. This can be a good way to cool or heat two or three rooms that are reasonably close together, when separate split-systems or a ducted system aren’t possible due to space limitations.
  • Ducted: The best option for temperature control throughout a large home, this consists of a central unit connected by ducts to air outlets and sensors in each room, with a control panel to set the target temperatures and the zones of the house to cool or heat. See our separate ducted air conditioner buying guide for more details. Price range: £5000+.
  • Wall/window: These models are usually installed in a window or external wall, and can cool rooms and open-plan areas of up to 50 square metres. Smaller units can be plugged into a normal power point; larger ones may require additional wiring. We don’t currently include these models in our reviews, because there are fewer on the market now, as split-systems are more efficient and have become more affordable in recent years. Price range: £400–£1100.

    Types of indoor unit

  • High wall: the most common form of split-system, with the indoor unit mounted high on a wall. This allows the air flow to easily blow across the room, and the cool air will sink down and push the hot air up and away.
  • Floor-mounted: the indoor unit is wall-mounted but at floor level — this might better suit some rooms, and could be a better option if you mainly use the unit for heating, as the hot air will come out at your level and rise to the ceiling.
  • Cassette: these have the indoor unit mounted in the ceiling. Some models can be mounted in either the ceiling or the floor.
  • Choosing the right capacity

    Cooling and heating capacities (sizes) are rated in kilowatts (kW). A small room might require a 2.5kW model, while a large open-plan area might need 6kW or more. It’s important to accurately calculate the required cooling or heating capacity of your new air conditioner.

    Some installers and online calculators offer only a simplistic analysis and may tend to recommend a larger capacity than you really need. A proper calculation takes all the room’s details into account:

  • The size of the room: length, width and height.
  • The type of room: living room, open-plan living room and kitchen, bedroom, etc.
  • The size and orientation of the windows and glass doors. A large south window can let in a lot of heat in summer.
  • Shading and curtains on the windows.
  • Insulation of the floor, ceiling, and walls.
  • The local climate.
  • Delta T Cooling is currently looking into options for building a capacity calculator to help you determine the right size of air conditioner for your needs. Meanwhile, try the size calculator on

    Choose a model with equal or slightly greater capacity for the room. For example, if you calculate the room needs a 6kW model, then look for an air conditioner with rated cooling capacity in the range 6kW to 6.5kW (roughly). It’s probably a safer bet to get a model slightly above the required capacity than slightly below it; a little extra grunt may help in extreme temperatures. But don’t go too much above the required capacity.

  • Models too powerful for the room size may run frequent short cycles to achieve the target temperature – which is like tapping the accelerator in your car to maintain speed instead of applying steady pressure. This can result in the room getting too cold or hot; inadequate dehumidification (i.e. not drying the air enough. making the room feel less comfortable); increased power usage and running costs; and wear and tear on the system.
  • Underpowered models may have to run more often at maximum output, dry the air too much and you’ll similarly suffer excessive wear.
  • Running costs

    Heating and cooling appliances account for about 40% of the energy usage of the average home. To save money when running your air conditioner, there are several things you can do.

  • Size: Having the correct size of air conditioner is an important first step (see Choosing the right capacity).
  • Star ratings: a model with more stars will be more efficient and use less power than a model with fewer stars.
  • Delta T Cooling air conditioner reviews rate each model for cooling and heating efficiency more precisely than the star ratings, and give an indicative running cost for each model.
  • Make your home as energy-efficient as possible; see our top 10 tips on keeping your home cool efficiently and effectively.
  • Use Economy mode (“Eco mode”) if your air conditioner has one.
  • Set the thermostat (target temperature) to a reasonable temperature so the system doesn’t have to work too hard and use more power than really necessary.
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