For most homes, setting air conditioning heating somewhere between 18°C and 21°C provides a sensible balance between comfort and energy use. Energy Saving Trust recommends this general indoor heating range for most people. A useful starting point for an air to air heat pump is around 20°C, then adjust it gradually to suit the room and your personal comfort. Turning the temperature up to 28°C will not make the room warm up faster.
At a Glance
If you are short on time, here is what you need to know.
What temperature should I set air conditioning to for heating? Around 18°C to 21°C is a sensible range for most homes. (energysavingtrust.org.uk)
Where should I start? ClimateWorks would normally suggest trying around 20°C and making small adjustments from there.
Will setting it to 30°C heat the room faster? No. A higher thermostat setting does not make the system produce heat faster simply because the number is higher. Energy Saving Trust gives the same advice for home heating controls generally. (energysavingtrust.org.uk)
Should I leave a heat pump running steadily? Heat pumps generally perform best when allowed to maintain a relatively stable temperature rather than repeatedly recovering from very large temperature drops. (energysavingtrust.org.uk)
Should every room use the same temperature? No. A bedroom may feel comfortable cooler than a home office or living room.
Does a higher setting increase running costs? Generally, yes. Maintaining a larger temperature difference between indoors and outdoors increases the amount of heat the building loses.
Reading time: 11 to 13 minutes
Last reviewed: September 2026
What Does the Temperature on Your Air Conditioning Remote Actually Mean?
This sounds obvious, but it causes a surprising amount of confusion.
When you select:
20°C
you are asking the system to work towards approximately that room temperature.
You are not selecting 20 percent heating power.
Likewise, selecting:
30°C
does not mean the system suddenly becomes a more powerful heater.
The air conditioning system decides how hard it needs to work based on factors such as:
- Current room temperature
- Selected temperature
- Outdoor temperature
- System capacity
- Sensor readings
- How quickly the room is losing heat
Modern inverter equipment then adjusts its compressor and fan operation according to demand.
Why 18°C to 21°C Is a Good Starting Range
Energy Saving Trust recommends setting home heating to the lowest comfortable temperature, which for most people is somewhere between 18°C and 21°C. (energysavingtrust.org.uk)
That does not mean every person needs exactly the same temperature.
Comfort is personal.
One person might be comfortable at 19°C.
Another may prefer 21°C.
The important point is that most homes do not need to be maintained at 25°C or 26°C throughout winter to feel comfortable.
For residential air conditioning heating, ClimateWorks would normally suggest starting at approximately:
20°C
Use the room normally.
Then adjust it by one degree if necessary.
That produces a much more useful result than immediately selecting an extreme temperature.
ClimateWorks Insight
The first few days of winter heating are usually when homeowners experiment too much.
20°C feels slow.
They change it to 24°C.
Then 28°C.
Then lower it again.
Then switch modes.
The system never gets a chance to settle.
Modern inverter heating works best when you choose a sensible temperature and give the equipment time to establish stable conditions.
The remote control should not need constant attention.
Why Setting the Temperature Higher Does Not Heat the Room Faster
Imagine your home office is currently 14°C.
You want it to reach 20°C.
If you set the controller to 20°C, the system already knows there is a significant heating requirement.
It can increase output accordingly.
Changing the target to 30°C does not magically increase the heating capacity of the equipment.
Energy Saving Trust makes exactly this point with domestic heating controls.
Turning the thermostat higher does not make the home heat faster. (energysavingtrust.org.uk)
All you have changed is the point at which the system believes it should eventually reduce its heating demand.
If you forget to turn it back down, the room can become unnecessarily warm and use more electricity.
Should You Leave Air Conditioning Heating On?
This depends on how the room is used.
There is an important difference between a heat pump and traditional assumptions about heating.
Energy Saving Trust notes that heat pumps often work most effectively when allowed to run steadily rather than being repeatedly switched on and off in the same way as some conventional heating systems. (energysavingtrust.org.uk)
That does not mean heating an empty room at full comfort temperature twenty four hours a day.
It means avoiding unnecessary extremes.
If a home office is occupied throughout the working day, maintaining 19°C or 20°C can be more sensible than allowing it to become extremely cold and then repeatedly demanding a rapid recovery.
The best control strategy depends on:
- How quickly the room loses heat
- How often it is occupied
- Insulation
- Outdoor temperatures
- Your electricity tariff
What Temperature Should You Use in a Home Office?
A home office is normally occupied for long periods.
You are also relatively inactive while sitting at a desk.
For many people, approximately:
19°C to 21°C
will provide a comfortable working environment.
Start at 20°C.
If you feel cold after the room has genuinely stabilised, increase it slightly.
If you feel too warm, reduce it.
Do not judge the temperature during the first five minutes after switching the system on.
The room itself may still be cold.
Walls.
Floor.
Furniture.
Desk.
All of these surfaces absorb heat while the space warms.
What Temperature Should You Use in a Garden Room?
Garden rooms can behave very differently.
They may cool down quickly overnight because the building is exposed on almost every side.
If the room is used as an office, approximately 20°C is again a sensible starting point.
But insulation quality has a major effect.
A poorly insulated garden building may require substantially more energy to maintain 21°C than a well insulated room inside the house.
The answer is not necessarily to keep increasing the thermostat.
If the system is working continuously and struggling to maintain a sensible temperature, the building heat loss and system sizing should be considered.
What About Bedrooms?
Bedrooms often do not need to be as warm as living spaces.
Many people prefer a cooler room for sleeping.
If you are using air conditioning heating in a bedroom before going to sleep, a setting around:
18°C to 20°C
may be enough for many homeowners.
Personal comfort still matters.
The important point is that using a reversible system for heating does not mean every room needs one identical setting.
Independent room control is one of the biggest advantages of residential split air conditioning.
Conservatories Need More Care
Conservatories can have significant winter heat loss because of their glazing.
Setting the system to 25°C does not solve that underlying problem.
If the room loses heat faster than the equipment can replace it, the system will simply continue operating at high demand.
For a conservatory, we would still normally begin with a sensible comfort temperature around 19°C to 21°C.
The bigger questions are:
- Is the system correctly sized?
- How much glazing is there?
- What type of roof does the conservatory have?
- Is the space open to the main house?
- How well insulated is it?
A thermostat cannot compensate indefinitely for poor building performance.
Why Higher Temperatures Cost More
Heat naturally moves from warmer spaces towards colder ones.
During winter, your home is warmer than outside.
The greater that temperature difference becomes, the faster heat tends to escape through the building fabric.
So imagine the outdoor temperature is 5°C.
Maintaining the room at 20°C creates a 15 degree difference.
Maintaining it at 25°C creates a 20 degree difference.
The second room generally requires more heating energy.
Energy Saving Trust currently estimates that reducing a typical thermostat setting from 22°C to 21°C can produce meaningful annual energy savings in a conventionally heated home. (energysavingtrust.org.uk)
The exact financial saving cannot simply be transferred directly to one air conditioning system, but the principle remains the same.
Do not maintain a higher indoor temperature than you actually need.
How Does Inverter Heating Help?
Modern residential air conditioning does not simply operate at maximum output until the room is warm and then completely stop.
Inverter technology allows the system to change its output.
When the room is cold, heating demand is high.
As the room approaches the selected temperature, the system can reduce its output.
Once conditions stabilise, it can concentrate on replacing the heat being lost from the room.
This is why steady operation can feel very different from a fan heater.
The system is designed to maintain temperature rather than repeatedly create bursts of intense heat.
Does Airflow Direction Matter in Heating Mode?
Yes.
Warm air rises.
If a wall mounted indoor unit blows warm air horizontally across the ceiling, much of the heat can remain above the occupied area.
During heating, directing airflow further down into the room can improve comfort.
Fan speed matters too.
Very low fan speed may feel quiet but may not move warm air far enough in a large room.
A medium or automatic fan speed often distributes heat more effectively.
This is particularly relevant in:
- High ceiling rooms
- Open plan areas
- Conservatories
- Larger home offices
Do not try to solve poor air distribution simply by increasing the temperature setting.
Why Does the Indoor Unit Sometimes Stop Blowing Warm Air?
This is usually normal.
During winter, an air source heat pump may occasionally need to defrost its outdoor heat exchanger.
During this process, indoor heating can temporarily reduce or pause.
You may notice:
- The indoor fan slowing
- Warm airflow stopping briefly
- Steam around the outdoor unit
- Water beneath the outdoor unit
That does not automatically indicate a fault.
The system is managing frost so it can continue extracting heat efficiently.
Once defrost finishes, normal heating resumes.
Increasing the thermostat during defrost will not make the process finish faster.
A Typical ClimateWorks Hampshire Example
A homeowner installs air conditioning in a garden office.
On the first cold morning they enter the room at 8am.
The temperature is 12°C.
They set the air conditioning to 28°C because they want the room warm quickly.
Twenty minutes later they reduce it to 22°C.
Then 20°C.
The better approach would have been to select around 20°C from the beginning and allow the system to do its job.
Once the room reaches temperature, the inverter can reduce its output and maintain comfort.
Simple settings usually produce better results.
A Typical Berkshire Bedroom Example
Another homeowner uses bedroom air conditioning for summer cooling and discovers heating mode during winter.
They initially set the bedroom to the same 21°C used in the living room.
It feels too warm overnight.
Reducing the bedroom setting to approximately 18°C or 19°C creates a more comfortable sleeping environment while still preventing the room becoming excessively cold.
This demonstrates the advantage of room by room temperature control.
You do not need one temperature for the whole house.
Should You Use Auto Mode for Winter Heating?
Usually, we prefer homeowners to select Heat mode deliberately when they want heating.
Auto mode allows the equipment to decide whether heating or cooling is required according to its sensor readings.
In some rooms, sunlight or other heat sources can temporarily influence those readings.
This may create behaviour the homeowner does not expect.
A simple winter rule works well:
If you want heat, select Heat mode.
Then choose your desired temperature.
Allow the system to stabilise.
Common Winter Heating Mistakes
Setting 28°C Because the Room Is Cold
This does not make the unit heat faster.
Constantly Changing the Set Temperature
Give the inverter system time to stabilise.
Using Auto Mode Without Understanding It
Select Heat mode when heating is what you want.
Using Very Low Fan Speed in a Large Room
Warm air may not travel effectively through the space.
Turning the System Off the Moment the Room Feels Warm
Allowing an efficient heat pump to maintain a stable temperature can often provide better comfort than repeated large temperature swings.
Ignoring Heat Loss
If a room cannot maintain 20°C, investigate the building and system design rather than simply selecting 30°C.
Dr Julian Carter's Expert Commentary
“The thermostat is a target, not an accelerator pedal. Setting an air conditioner to 30°C because the room is cold does not give the compressor another level of heating capacity. For most homes, start around 20°C, select Heat mode and allow the system to stabilise. Once you understand how an inverter heat pump behaves, you normally find yourself touching the remote control far less.”
Dr Julian Carter
Technical & Compliance Director
ClimateWorks
How the ClimateWorks Process Works
If winter heating is going to be important, tell us before the system is selected.
Step 1. Get Your Online Guide Price
Use the ClimateWorks online quotation tool.
Tell us which rooms you want to heat and cool and receive an initial guide price.
Step 2. Request a Site Survey
If the guide price fits your expectations, request a site survey.
Where heating is important, we consider:
- Room heat loss
- Room dimensions
- Insulation
- Glazing
- Ceiling height
- Indoor unit position
- Air distribution
- Outdoor unit location
- System capacity
- How frequently the room will be used
Step 3. Receive Your Final Price
Following the survey, we provide the final quotation based on the agreed installation.
You can then accept or decline.
A system expected to provide meaningful winter heating should be selected with heating in mind from the beginning.
Why Homeowners Choose ClimateWorks
The system should be simple to live with once it has been installed.
ClimateWorks works with homeowners across Hampshire, Berkshire and Surrey to design air conditioning around year round use.
That means considering how the same equipment will behave in January as well as July.
Good residential air conditioning should not require constant adjustment.
Choose the temperature.
Let the system maintain it.
Use the room.
Frequently Asked Questions
What temperature should I set air conditioning to for heating?
For most people, somewhere between 18°C and 21°C provides a sensible balance between comfort and energy use. ClimateWorks generally suggests starting around 20°C. (energysavingtrust.org.uk)
Will setting air conditioning to 30°C heat the room faster?
No. A higher thermostat setting changes the target temperature, not the maximum heating capacity. (energysavingtrust.org.uk)
Should I leave air conditioning heating running all day?
It depends on how the room is used, but heat pumps generally work well when maintaining relatively stable conditions rather than repeatedly recovering from very large temperature drops. (energysavingtrust.org.uk)
What temperature should a home office be?
Many people will be comfortable around 19°C to 21°C. Start around 20°C and adjust according to personal preference.
What temperature should a bedroom be when heating?
Bedrooms often suit slightly cooler temperatures. Around 18°C to 20°C may be comfortable for many people.
Does lowering the thermostat save electricity?
Generally, yes. Maintaining a lower comfortable indoor temperature reduces heat loss and therefore heating demand.
Why does my air conditioning stop heating occasionally?
During cold weather the system may enter a normal defrost cycle to remove frost from the outdoor heat exchanger.
Should I use Heat mode or Auto mode?
If you specifically want heating, selecting Heat mode usually gives clearer and more predictable operation.
What fan speed should I use for heating?
Automatic or medium fan speeds often distribute warm air better than permanently using the lowest fan setting, particularly in larger rooms.
Why will my room not reach 20°C?
Possible reasons include excessive heat loss, incorrect system sizing, poor airflow, very cold outdoor conditions or a fault. If the system regularly struggles, it should be assessed rather than simply setting the thermostat higher.
References
Energy Saving Trust
Current guidance recommends heating most homes to the lowest comfortable temperature, usually between 18°C and 21°C, and explains that turning a thermostat higher does not make a property heat faster. (energysavingtrust.org.uk)
Energy Saving Trust
Its 2026 heating guidance notes that heat pumps generally perform best when operated steadily and again recommends thermostat settings between approximately 18°C and 21°C for most people. (energysavingtrust.org.uk)
Energy Saving Trust
Current air to air heat pump guidance explains that these systems provide room heating and cooling and that real running costs depend on the system design, existing heating system and how efficiently the heat pump is operated. (energysavingtrust.org.uk)
Department for Energy Security and Net Zero
Government research published in July 2026 examines the energy performance, running costs and suitability of reversible air to air heat pumps across different UK home types. (gov.uk)
Author Bio
Dr Julian Carter is Technical & Compliance Director at ClimateWorks and specialises in residential air conditioning, air to air heat pumps and year round indoor comfort. Drawing on practical experience from installations across Hampshire, Berkshire and Surrey, Dr Carter provides evidence based guidance to help homeowners understand how to use modern heating and cooling systems efficiently and comfortably throughout the year.
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