By Bournemouth Air Conditioning. Published .
Most modern wall-mounted air conditioning units heat as well as cool. Switched to heat mode, the unit works as an air-to-air heat pump, taking heat from the outside air and moving it indoors, even on a cold morning.
If you had a unit fitted for the summer and have never pressed the heat button, here is how it works, how to get the best from it this winter and what is normal behaviour.
How an air conditioner heats a room
In cooling mode the system takes heat out of the room and releases it outside. In heat mode a valve reverses the flow of refrigerant, so the outdoor unit collects heat from the outside air and the indoor unit releases it into the room.
Because it moves heat rather than making it, a heat pump can deliver more heat than the electricity it uses. That is the difference between it and an electric fan heater or an oil-filled radiator, which turn each unit of electricity into one unit of heat. The exact efficiency depends on the model and on how cold it is outside, and it falls as the outdoor temperature drops.
Check your model's specification for its heating capacity and the lowest outdoor temperature it is designed to heat at. A cooling-only unit has no heat mode at all.
Settings that work in winter
- Pick a comfortable temperature and leave it there. Heat pumps work best holding a steady temperature rather than racing up from cold, and setting it much higher does not heat the room any faster.
- Use the timer or schedule to bring the room up to temperature before you need it, rather than switching on as you walk in.
- Point the louvres down. Warm air rises, so aiming the airflow at the floor gives a more even room.
- Use auto fan speed, or the quiet or night mode at bedtime if your unit has one.
- Keep the door closed. A wall unit is sized for a room, not the whole house.
A south coast winter is milder than one inland, but damp, windy days are common in Bournemouth and Poole. A steady setting copes with that far better than short blasts of heat.
Why it sometimes stops blowing warm air
On cold, damp days, frost forms on the outdoor unit's coil. To clear it, the system runs a defrost cycle. It briefly reverses, the indoor fan slows or stops, and the outdoor unit may give off a cloud of steam and drip water. After a few minutes it goes back to heating.
This is normal. You may also notice a short wait after switching on before any warm air comes out. Many units hold the indoor fan until the coil has warmed up, so they do not blow cold air at you.
What is not normal is a unit that spends most of its time defrosting, or an outdoor unit that ices up solid and stays that way. That points to an airflow problem, a fault or a refrigerant leak, and it is worth booking an air conditioning repair visit.
Keep the outdoor unit clear
The outdoor unit needs to breathe to collect heat. Keep leaves, garden furniture and covers away from it, and do not wrap it up for the winter. The meltwater from defrosting needs somewhere to go, so check it is not dripping onto a path where it could freeze.
Near the coast, salt and grime on the coil also reduce performance. A service cleans the coils, clears the drain and checks the system in both heating and cooling modes. Our guide on how often air conditioning should be serviced explains the intervals.
Is it worth using air conditioning as heating?
For a single room, such as a home office, a loft conversion or a garden room, a reversible unit is often a sensible way to take the chill off without running the central heating for the whole house. Whether it costs less than gas in your case depends on your tariffs, your boiler and how you use the room, so compare your own unit rates rather than relying on a general rule.
If you are thinking of adding a unit mainly for heating, look for a model with a good heating rating at low outdoor temperatures, and get the size right for the room. Planning rules also favour units that heat. In England, a unit used only for cooling does not count as permitted development, as we explain in do you need planning permission for air conditioning.
Book a survey or service
We install and service reversible systems across Bournemouth, Christchurch and the rest of the area. See home air conditioning for new installs, or book a check through our air conditioning servicing page. Call 07910 686513.
Related services: Air conditioning servicing, Air conditioning repairs, Home air conditioning.