How should I use air conditioning for heating during UK winter months?

You rely on air conditioning for heat.
Winter arrives.
Comfort drops.

Air conditioning works well for heating in the UK. Problems start when settings stay unchanged from warmer months or when expectations do not match how the system behaves in cold weather.

Why winter use needs a different approach

Winter changes how rooms behave.

External temperatures drop.
Walls and floors lose heat faster.
Windows pull warmth out of the space.

Air conditioning can handle this, but only when settings support steady operation rather than short bursts.

Start with the correct operating mode

Heating mode must be selected.

Cooling or auto mode will undermine winter comfort.
Auto mode reacts to short temperature changes.
Heating mode focuses on maintaining warmth.

Always confirm the controller shows HEAT or a sun symbol.

Choose a realistic temperature setting

Set a sensible target temperature.

21°C to 22°C works well for most homes.
Higher settings do not heat rooms faster.
Lower settings reduce heating demand.

Pick a target and leave it alone.

Consistency matters more than the number.

Use fan speed to spread heat properly

Fan speed controls how heat moves.

Low fan speed feels gentle but warms slowly.
Medium fan speed spreads heat evenly.
High fan speed can feel cool at first.

In winter, start on medium fan speed for the first 10 to 15 minutes. Reduce it once the room warms.

Allow enough time for warmth to build

Heating with air conditioning is not instant.

Cold surfaces absorb heat first.
Air movement can feel cool early on.

Give the system time to stabilise. Judge comfort after at least 15 minutes rather than immediately after switching it on.

Avoid switching the system on and off

Frequent switching causes problems.

Each restart delays heating.
The system never reaches stable output.
Rooms feel colder overall.

During winter, steady operation produces better comfort than short bursts.

Be cautious with auto mode

Auto mode sounds helpful.
In winter, it often causes issues.

Sunlight, cooking, or people in the room can trigger unwanted cooling or reduced heating. This creates temperature swings and cold airflow.

Manual heating mode gives more predictable results.

Check timers before winter starts

Timers set in summer often remain active.

They can
Turn heating off overnight
Lower temperatures unexpectedly
Switch modes automatically

Review and disable timers that no longer suit winter use.

Understand defrost behaviour

In cold weather, outdoor units may frost.

During defrost
Indoor heating pauses
Airflow may slow or stop
Cool air may appear briefly

This is normal winter behaviour. Heating resumes automatically once defrost finishes.

Room factors that affect winter heating

Some spaces need more time and support.

Large windows
High ceilings
External walls
Open plan layouts

In these rooms, allow longer warm up periods and avoid frequent setting changes.

Common winter mistakes to avoid

These cause most heating complaints.

Leaving cooling or auto mode active
Changing temperature repeatedly
Using very low fan speed
Turning the system off too soon
Standing directly under the unit

Each one disrupts heat delivery.

When air conditioning struggles in winter

In very cold conditions, output can reduce.

The system may still heat but not reach high target temperatures. This is normal behaviour for air source systems.

Performance improves as outdoor temperatures rise.

When to seek professional support

Contact a specialist if
Heating mode is active with no improvement after 20 minutes
The system shuts down repeatedly
Error codes appear
The outdoor unit does not operate

Before calling, note the mode, temperature, fan speed, outdoor temperature, and how long the issue has been happening.

This helps speed up diagnosis.

Related guidance

Further residential air conditioning guidance is available at
https://www.climateworks.co.uk/residential-air-conditioning

References

UK Government guidance on heat pump operation
https://www.gov.uk/guidance/heat-pumps-how-they-work

Building Regulations Approved Document L
https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l

ClimateWorks residential usage data from installations across Hampshire, Berkshire, Surrey, and Oxfordshire between 2022 and 2025

Author

Dr Julian Carter
Technical and Compliance Director
ClimateWorks

Dr Julian Carter has over 20 years of experience in building services engineering, air conditioning system design, and regulatory compliance. He advises on residential and commercial projects across the UK, covering system selection, installation standards, commissioning, and real world performance.

As Technical and Compliance Director at ClimateWorks, he oversees technical governance, installer training, fault diagnosis, and customer education. His work focuses on reducing user related issues, improving system reliability, and ensuring air conditioning systems perform consistently throughout their service life.

‍