Can Air Conditioning Heat a Room in Winter?

Yes, air conditioning can heat a room in winter and does so more efficiently than you might think. Whilst many of us think of air con as a way to cool down in summer, its reverse-cycle split system lets you enjoy much-needed warmth during the colder months.

How air conditioning warms a room in winter: Summary

• The system reverses its normal operation to warm a room rather than cool it.
• Thermal energy is found in cold air, so the system extracts heat from the outside air.
• In very cold weather, the system will work harder to raise temperatures.
• Unlike traditional electric heaters, energy is not converted directly into heat; instead, it moves existing heat through a cycle.
• Air-to-air systems can warm an individual room very quickly.
• Correct sizing matters: an undersized unit will struggle in a large or poorly insulated room.

How air conditioning heats a room

Air conditioning heats a room by reversing its operation. In the summer, it moves heat from inside your house and displaces it outside, but in winter, or when temperatures are low, it extracts heat from the outside air.

This may sound a little confusing; if it’s cold outside and your system uses that air, it stands to reason that your home will get cold too, right? Wrong! There is still heat energy in cold air, so the system extracts the heat from it before the unit works through a series of processes resulting in warm air blown across the room.

1. Refrigerant in the outside unit absorbs heat from the outside air.
2. A compressor raises the pressure and temperature of the refrigerant.
3. This hot refrigerant passes to the indoor unit.
4. A fan blows the room air across the warm coil in the unit.
5. Warmed air circulates and the cooled refrigerant cycles back out.

Will it still work during winter weather?

Yes, there is still heat in the outside air, even when temperatures are very low. Quality systems are designed to work in cold weather, with many able to function in temperatures as low as -15°C. This makes them more than suitable for a regular Sussex winter. However, there are two things to remain aware of when temperatures plummet.

• The system will deliver less heat: The colder it gets outside, the harder the system works and the less heat it provides.
• A defrost pause is normal, and not a fault: In cold, damp weather, the unit may pause its heating cycle for a few minutes. This is perfectly normal and is the system going into defrost mode so it can clear frost from the coil.

Is air conditioning in winter cheaper to run than normal heating?

It certainly can be. The heating efficiency of your air conditioning or heat pump is measured by its SCOP, or Seasonal Coefficient of Performance.

A SCOP of 2 means that for every kWh of electricity, you get 2kWh of heat. Every unit should have a SCOP figure on its energy label so you can get an idea of how efficient it is. As per the Commission Delegated Regulation (EU) No 626/2011 (retained in UK law), SCOP bands are as follows:

The full scale reaches G, where the SCOP is anything below 1.90. A good modern unit sits around the A-rated level.

In terms of actual cost, using the current energy price cap, we can see how much you might spend per unit of heat.

*Please note, these prices are based on the current Ofgem price cap (Oct-Dec 2026) and are set to rise. Total costs will vary by unit, usage, condition, and energy tariff.

The benefits of heating with air conditioning

Using air conditioning for heating can be extremely beneficial if the unit suits the room size it heats. Benefits include:

• Low running costs
• Faster heating
• Room-by-room zoning
• No gas supply or flue needed
• Built-in timer and thermostat

When to use air conditioning instead of your central heating

If the weather is cold, but not excessively cold, and you need to warm up a single room, you could either heat it with your air con unit or switch on the central heating and warm up the entire house. Cost-wise, the air con wins in this scenario. However, in the depths of winter, when each room feels too cold to be comfortable, the central heating will remain your best bet.

What your air con can’t do in the winter

Whilst an air conditioner can warm a room in winter, it does have limitations that you’ll need to be aware of:

• It only heats the room it is in. For multiple rooms, you’ll need multiple units.
• Your hot water does not get heated, so you’ll still need a boiler or an air-to-water heat pump to get your radiators warm.
• It won’t be able to warm poorly insulated rooms to a high level.
• It may struggle to warm up rooms that are too big for the unit’s capabilities.

An assessment from a professional air conditioning installer determines which size unit best fits the room and whether multiple units are a cost-effective option for your home.

Which rooms benefit from air conditioning in the winter?

If you use your air conditioning as heating, it benefits some rooms more than others. Small units, for example, may struggle to warm a large open-plan living room/dining room space, but could heat up a home office perfectly.

For a single unit, you’ll get the best heating results in the following rooms:

• Home offices: One room to heat without having to switch the whole heating system on.
• Bedrooms: Warm them in the winter and cool them in the summer, all from one unit.
• Extensions or loft conversions: Your central heating may not reach them, so adding an air conditioning unit means you can keep them warm when they are occupied.
• Conservatories: In the winter, they can get cold quickly; in the summer, they can get warm fast. Adding conservatory air conditioning means you can still enjoy this part of your house, regardless of the time of year.

Air conditioning vs a whole-house heat pump

Air conditioning can be a great option for some added warmth in winter, but it will only warm the room it is in. An air-to-water heat pump, on the other hand, warms your radiators or underfloor heating, making it possible for the whole house to be heated.

Let’s compare them, so you have a clearer idea of their benefits and drawbacks.

Considering air conditioning this winter?

It might not be as strange as you first thought, and you’ll benefit from cooling the room in the warmer months too. At Sussex Air Conditioning & Heat Pumps Ltd, we install heat pumps and air conditioning units for domestic and commercial properties across Sussex, using our extensive industry knowledge and years of experience to deliver consistently high standards. Contact us today for a free quote.