The quick answer: yes, and you may use it more than you expect
Fixed air conditioning can be useful well beyond summer. If your system is a reversible air-to-air heat pump, it can warm the rooms it serves when the weather turns colder. Check the model's heating specification: the answer is not the same for every appliance sold as an air conditioner.
For Nick, heating has become a substantial part of using AC at home: "I use my air conditioning as much for heating as I do for cooling, possibly more. I've been really pleased with how it heats my home. It also feels cheaper to run."
That last point is worth examining. Comfort is something you can experience directly; establishing a saving needs a fair comparison. This guide explains how heating mode works, what changes in winter and how to compare the energy cost with gas or a plug-in electric heater.
How air conditioning heats a room
A reversible split system transfers heat. In heating mode, its outdoor unit collects heat from the outside air and the system delivers it indoors. Electricity powers that process. In cooling mode, the direction of heat transfer reverses.
This helps explain why the electricity going into a unit can be much lower than the heat it delivers. A system operating at a coefficient of performance, or COP, of 3 provides three units of heat for each unit of electricity consumed. COP describes performance under particular conditions, rather than a fixed promise for every hour of use.
For seasonal comparisons, look for SCOP, the seasonal heating efficiency rating. SEER refers to cooling. Ask an installer to explain the heating rating and capacity of the proposed indoor and outdoor unit combination. A strong cooling specification alone does not answer the winter-heating question.
Three ways you might use AC for heating
These are examples to help frame a conversation with an installer, rather than predictions for a particular house.
- One room while you work. If you spend the day in a home office, compare heating that space with how you currently use your heating. Keep the room temperature and occupied hours comparable. Any reduction from heating fewer rooms is separate from the efficiency of the AC itself.
- Several rooms through the day. Think about where people actually spend time and which doors are usually closed. Ask how the proposed system will serve those rooms together, rather than assuming warm air from a hallway unit will reach everywhere.
- The main heating for your home. Ask for a whole-home design covering room heat demand, cold-weather capacity and any supplementary heating. Include bathrooms and other spaces without an indoor unit. Most standard air-to-air installations also need a separate way to provide hot water for taps and showers.
Is heating with AC cheaper?
It can be. A fair starting point is the cost of delivering the same amount of heat, rather than comparing the power ratings on two appliances.
The illustration below starts with Ofgem's average Direct Debit unit rates for Great Britain for 1 October to 31 December 2026: 26.32p/kWh for electricity and 7.97p/kWh for gas. These are dated examples, not a quote for your tariff. The gas rate includes VAT; no VAT is added to the electricity rate for this period.
Change the electricity and gas rates, assumed AC efficiency and assumed boiler efficiency to see how the comparison changes. COP means units of heat delivered per unit of electricity used. Use your own unit rates and treat the efficiency settings as scenarios unless you have evidence for your installation.
Explore the energy cost
What does the same heat cost?
Change the tariffs and efficiency assumptions to compare the same amount of heat. These are illustrative energy costs, not a prediction of your bill.
- AC heating8.77p
- Gas boiler8.86p
- Direct electric heater26.32p
AC costs 0.08p less per kWh of heat than gas.
AC matches gas at COP 2.97 with 90% boiler efficiency and these tariffs. COP means units of heat delivered per unit of electricity. The efficiency settings are assumptions, not measurements of your system.
Starting rates: Ofgem, 1 October to 31 December 2026, average Great Britain Direct Debit. The gas rate includes VAT; no VAT is added to the electricity rate for this period.
Running energy only. Excludes installation, servicing and standing charges. Your own tariff and achieved efficiency may differ.
What the comparison includes
At the starting assumptions, a direct electric heater costs 26.32p per kWh of heat. AC at COP 3 costs 8.77p, while a gas boiler at an assumed 90% efficiency costs 8.86p. That puts AC and gas very close. At COP 4, the AC figure falls to 6.58p; at COP 2.5, it rises to 10.53p and becomes more expensive than the gas example.
These figures compare running energy only. They exclude installation, servicing and standing charges. Keeping a gas connection can mean continuing to pay its standing charge, even when you use less gas. Heating costs for hot water and rooms served by other appliances need to be counted separately.
For an existing AC system, comparing the next unit of heat is useful. For a new purchase, compare the full installed and ongoing cost as well. Energy Saving Trust says UK evidence on air-to-air savings remains limited, so a neat worked example should not become a guaranteed household saving.
What happens when it gets cold outside?
Heating capability depends on the model and conditions. A product's minimum operating temperature is not a promise that it will deliver its full rated heat output at that temperature. Ask for heating capacity and efficiency at the outdoor conditions used to design your installation.
Frost can form on an outdoor coil, and systems use a defrost cycle to clear it. Heating may pause while that happens. The detail and timing depend on the equipment, so check the operating instructions rather than treating every pause as a fault. Persistent loss of heat or a fault indication deserves the installer's attention.
The practical question is whether the system can keep the required rooms comfortable through cold weather. That needs a room-by-room assessment, not a choice based only on a headline cooling capacity. Government modelling also highlights the importance of supplementary heating and hot-water arrangements when assessing the whole home.
Making heating mode comfortable
Warm-air heating can feel different from radiators. Position and airflow matter: discuss where you sit or work, how the fan sounds at the output you need, and whether furniture will obstruct circulation. Ask about the whole room, not just the temperature near the unit.
Use the manufacturer's guidance for selecting heating mode, setting a comfortable temperature and adjusting the fan or airflow. Avoid repeatedly turning the setting up and down to force a blast of heat. Clean accessible filters as instructed and keep the outdoor unit clear of leaves and obstructions. Follow the servicing requirements for your equipment.
Heating does not remove the need for ventilation. Standard split AC generally recirculates room air, so continue the home's normal ventilation arrangements.
What to ask before accepting a quote
Bring your existing tariff details and explain when each room is used. A useful proposal should make the assumptions clear enough to compare with another installer's design.
- Which rooms will this design heat, and what provision is needed elsewhere?
- What room heat-loss assessment supports the proposed sizing?
- What heating capacity is available in the cold conditions used for the design?
- What do the COP and SCOP figures mean for this equipment combination?
- How should I use the controls, and what should I expect during defrosting?
- How will the outdoor unit's water drainage and position work in winter?
- What assumptions support the running-cost estimate, and what costs are excluded?
- If this replaces my main heating, how will hot water and supplementary heating be provided?
Common questions
Can air conditioning heat a home in winter?
Yes, a suitable reversible fixed system can provide heating. Its capacity, the building's heat demand and the installation design determine which rooms it can keep comfortable in cold weather.
Is AC heating cheaper than gas?
Sometimes. With the example tariffs in this guide and an assumed 90% efficient gas boiler, AC reaches a similar energy cost at COP 2.97. Higher efficiency reduces its energy cost; lower efficiency increases it. Your own tariff can change that comparison.
Is it cheaper than a plug-in electric heater?
At the same electricity tariff, AC operating above COP 1 needs less electricity to deliver the same heat than a direct electric heater. That comparison does not include the cost of buying, installing or servicing the AC system.
Can I replace my central heating with AC?
It may be possible with a suitable whole-home design. Assess every room, cold-weather performance, supplementary heating and hot water before removing an existing system. Adding one unit for summer cooling is not a whole-home heating assessment.
Will it heat water for my taps and shower?
Most standard air-to-air systems will not. Some specialist arrangements can provide hot water, but do not assume an ordinary wall-mounted split installation includes it. Ask how your household's hot-water needs will be met.