A heat pump heating curve sets the relationship between outdoor temperature and the water temperature required for space heating. When outdoor conditions become colder, the system generally needs warmer water. In milder weather, it can use a lower flow temperature while maintaining indoor comfort.
A correctly adjusted heating curve helps the heat pump respond to changing heating demand without producing unnecessarily hot water.
What is a heat pump heating curve?
The heating curve tells the controller which flow temperature to target at different outdoor temperatures.
Flow temperature is the temperature of the water leaving the heat pump and entering the heating distribution system, such as radiators or underfloor heating.
For example, a home may need a higher flow temperature on a cold winter day than on a mild autumn afternoon. The heating curve allows the controller to make that adjustment automatically.
Our guide to heat pump flow temperature explains why this setting matters for efficiency.
How the heating curve works
An outdoor sensor measures the external temperature. The controller uses the configured heating curve to determine the target flow temperature.
The principle is straightforward:
- Colder weather: the controller generally raises the target flow temperature to meet greater building heat loss.
- Milder weather: it lowers the target flow temperature as heating demand falls.
- Warm weather: space heating may stop when the system’s configured heating limit is reached.
The exact relationship depends on the building, heating system and controller settings. There is no single curve suitable for every installation.
Why the heating curve matters
Heat pumps generally operate more efficiently when they can deliver heat at lower water temperatures, provided the emitters still supply enough heat to keep the rooms comfortable.
An unnecessarily high heating curve can result in overheating and higher electricity consumption. A curve set too low can leave rooms unable to reach their desired temperature.
The aim is to find the lowest suitable flow temperature across different weather conditions. This can support:
- Stable indoor comfort.
- More efficient space heating.
- Reduced unnecessary high-temperature operation.
- Better matching between the heating system and the building’s needs.
Actual results depend on the installation, controls and previous settings.
Heating curves and weather compensation
Using outdoor temperature to adjust the target flow temperature is known as weather compensation.
Rather than relying solely on a room thermostat to switch heating on or off, weather compensation changes the water temperature as outdoor conditions change.
Some systems also use indoor-temperature feedback to refine their response. The available functions depend on the controller and its configuration.
Weather compensation can be used with radiators, underfloor heating and other suitable emitters, provided the system is correctly designed and commissioned.
How to adjust a heat pump heating curve
Start with the installer’s recommended settings for the building and heating system. Record the existing settings before making adjustments.
A practical approach is to:
- Observe indoor temperatures during both mild and cold weather.
- Note whether the whole home is too warm, too cool or comfortable.
- Make small adjustments using the controller’s instructions.
- Allow the building time to respond before making another change.
- Review performance under different outdoor conditions.
Some controllers provide separate adjustments for the curve’s slope and its overall temperature offset. These have different effects, so follow the model-specific instructions or ask the installer to help.
If only one room is cold, check its radiator output, water flow and balancing before increasing the heating curve for the entire home.
Heating curve settings for different homes
The appropriate settings depend on:
- Building heat loss and insulation.
- Local outdoor conditions.
- Radiator or underfloor-heating capacity.
- Required indoor temperatures.
- Water circulation and hydraulic balancing.
A well-insulated home with underfloor heating may maintain comfort at relatively low flow temperatures. A radiator system may need higher temperatures, depending on radiator size and room heat loss.
Our guide to heat pump radiator sizing explains how to check whether existing radiators can meet a room’s heating requirements at the intended water temperature.
Smart controls and automatic adjustment
A heating curve sets the target flow temperature according to outdoor conditions. The heat pump controller applies this setting to help match space heating to the building’s needs.
Available monitoring and adjustment options depend on the heat pump model and control configuration. Remote access can make settings easier to view or adjust, but correct commissioning remains essential.
Common heating curve mistakes
Common mistakes include:
- Setting the curve higher than necessary.
- Lowering it until rooms cannot maintain comfort.
- Making several large adjustments at once.
- Changing settings again before the building has responded.
- Copying settings from a different property.
- Using a higher curve to compensate for poor balancing or undersized radiators.
Heating-curve adjustments concern space heating. Domestic hot-water settings should be managed separately according to the manufacturer’s and installer’s instructions.
Getting the balance right
The best heating curve is the one that maintains comfortable room temperatures with the lowest suitable flow temperature as outdoor conditions change.
Good results depend on the whole system: building insulation, correctly sized emitters, adequate water flow and properly configured controls.
Work with your installer to establish suitable initial settings and refine them through observation.
Frequently asked questions
What is a heat pump heating curve?
It is the relationship used by the controller to set the target space-heating flow temperature according to outdoor temperature.
Why is the heating curve important?
It helps the system maintain comfort while avoiding unnecessarily high water temperatures, which can reduce efficiency.
How do I know if my heating curve is too high?
Rooms may become warmer than intended, particularly under certain outdoor conditions. Other control settings can also cause overheating, so review the system with your installer before making large changes.
Can adjusting the heating curve improve efficiency?
Yes, if the current settings produce hotter water than the building needs. The benefit depends on the installation and its previous operating conditions.
Is the same heating curve suitable for every home?
No. The appropriate curve depends on building heat loss, emitter capacity, climate and indoor-temperature requirements.
