The short answer
The features that make the most day-to-day difference are an inverter, heating that copes with cold weather, a genuinely quiet lowest fan speed, good airflow control, useful timers and easy-to-clean filters. Many extras are pleasant rather than essential.
On this page
Specification sheets list dozens of features, and different manufacturers give the same idea different names. It's easier to judge them by what they actually do, and by whether you'll use them in a normal week. The features below are described in plain terms, so you can recognise them whatever they're called.
The essentials
| Feature | What it does | Why it matters |
|---|---|---|
| Inverter | Varies compressor speed to suit the room | Steadier temperature, quieter at low output |
| Heating | Runs the system in reverse to warm the room | Useful for much of the year |
| Low minimum fan speed | Keeps the indoor unit very quiet | Matters most in bedrooms |
| Dry mode | Takes moisture out with limited cooling | Helps on humid, mild days |
| Auto restart | Returns to its settings after a power cut | Saves resetting it |
Most split systems sold for homes have an inverter, but check on cheaper units, especially portable ones, many of which still switch fully on and off. What an inverter does explains the difference.
Heating matters for planning too. In England, an air-to-air system fitted under permitted development must not be used solely for cooling, so it needs to provide heating as well. The planning permission guide covers the other conditions.
Comfort features
- Airflow control. Louvres that swing up and down, and on many units left and right, let you spread air around the room or aim it away from people. Being able to fix the louvres in one position is as useful as the swing. See directing the airflow.
- Presence sensors. Some units detect where people are and direct air towards or away from them, or turn their output down when the room is empty.
- Sleep mode. Gradually adjusts the set temperature overnight and keeps the fan quiet.
- Quiet mode for the outdoor unit. Limits outdoor noise at the cost of some output, which can help where the unit is near bedroom windows.
- Boost mode. Runs at full output for a short time to bring a room to temperature quickly.
Control and scheduling
- Timers. An on and off timer is almost always included. A weekly schedule, on the remote or in an app, lets the system follow your routine without you touching it.
- Wi-Fi control. Built in or added with an adapter, it lets you control the system from your phone. Wi-Fi, apps and smart controls covers what to check.
- Wired wall controller. Some units can take a controller fixed to the wall, which is handy in homes where remote controls go missing.
- Temperature sensing where you sit. Some remotes measure the temperature at the handset and send it to the unit, which can give a truer reading than the sensor up near the ceiling.
Heating in cold weather
If you'll use the system to heat through winter, a few details on the specification sheet matter more than any extra:
- Operating range. This shows the lowest outdoor temperature the unit is designed to heat at.
- Heating output in the cold. Output falls as the temperature drops, so ask how much heat the unit gives at low outdoor temperatures, not just its rated figure.
- Base heater. Air-to-air heat pumps need to defrost from time to time in cold, damp weather. Some outdoor units have a small heater in the base to stop meltwater refreezing there.
- Low-temperature heating setting. Some units can hold a room at a low temperature, often around 8 to 10°C, to stop an empty room getting too cold.
Extras to weigh up
- Self-drying. Some units run the fan for a while after cooling to dry the inside of the unit, so it doesn't sit damp.
- Extra filters. Some models take additional filters designed to catch finer particles or reduce odours. They add a little to the cleaning and replacement routine.
- Air-treatment features. Some units include ionisers or similar technologies, with a range of manufacturer claims. They're separate from heating and cooling, so judge the unit on those first.
- Energy monitoring. Some apps show electricity use, which helps you spot patterns. The figure is often an estimate rather than a meter reading.
- Appearance. Finishes, colours and slimmer shapes are a matter of taste, and worth considering for a unit you'll look at every day.
Related guides
- What an inverter doesAn inverter lets the compressor change speed. Instead of switching on and off, the system runs hard to reach the setting, then slows down to match what the room needs, holding a steadier temperature with less noise.
- Wi-Fi, apps and smart controlsMany air conditioners can be controlled from a phone app over your home Wi-Fi, either built in or through an add-on adapter. An app lets you switch on, change settings and set schedules from anywhere, while the remote usually still works as normal.
- What air conditioning filters doAir conditioning filters catch dust and fibres before they reach the indoor unit's coil and fan, keeping air flowing freely and the inside of the unit cleaner. Most are washable mesh screens that need cleaning every few weeks in regular use.
- Sleep and quiet modesSleep mode usually shifts your setting by a degree or two over the first hours of the night, warmer when cooling and cooler when heating, and turns the fan down. Quiet mode slows the fan to cut noise, at the cost of some output.