Home / Blog / Guides

Guides

Heat pump flow temperature explained: the right setting for your home (UK 2026)

Last updated 2026-10-05

The short answer

Flow temperature is the temperature of the water a heat pump sends out to radiators or underfloor heating. Heat pumps generally work more efficiently when they can deliver the required warmth at a lower flow temperature, but the right setting depends on the home, the emitters and the weather.

There is no universal setting that is right for every property. A well-designed system should be able to keep rooms comfortable without relying on unnecessarily hot water. Radiators may feel warm rather than very hot, and the heating may run for longer at a steadier pace than a boiler system.

Flow temperature vs room temperature

Room temperature is the temperature you feel in the living space. Flow temperature is the water temperature inside the heating system as it leaves the heat pump. The water returns to the unit cooler after transferring heat to radiators or underfloor heating.

The heat pump uses electricity to move heat from outside into the home. In general, making it produce hotter water requires more work, so a lower flow temperature can improve efficiency. But the system still needs enough output to replace heat lost from the building, especially on colder days.

Why heat pumps often run at lower temperatures

Boiler systems are often operated at higher water temperatures and may heat radiators quickly in short bursts. A heat pump is commonly designed to run for longer periods, delivering heat steadily at a lower temperature. This approach can help the unit operate efficiently and maintain a more even indoor temperature.

That does not mean every heat pump should always run at the lowest possible setting. The design must balance efficiency with the home’s heat loss, the available radiator or underfloor-heating output, hot-water requirements and comfort preferences.

What is weather compensation?

Weather compensation uses an outdoor sensor and a heating curve to adjust the system’s flow temperature as the weather changes. When it is milder, the system can usually use cooler water; when it is colder, it may need to raise the flow temperature to deliver enough heat.

A correctly configured heating curve can reduce the need for manual adjustments. If your home is comfortable in mild weather but too cool during a cold spell, or overheats when the weather turns mild, ask your installer to review the curve and system settings.

How do radiators affect the setting?

Each radiator needs to emit enough heat to cover its room’s heat loss at the design conditions. A radiator that is too small for the room may require hotter water, while a larger emitter can provide the same heat at a lower temperature. Insulation, draughts, room layout and radiator balancing also matter.

You do not automatically need to replace every radiator. Ask for the room-by-room heat-loss calculation and the proposed radiator output at the design flow temperature. Our guides explain whether existing radiators can work and how a heat pump should be sized.

How to adjust your system safely

1. Check the controls first: understand whether you are changing the heating flow temperature, hot-water setting or room thermostat. They do different jobs.
2. Make small changes: if your installer has shown you how, adjust gradually and allow time for the home to respond.
3. Keep a note: record the setting, outdoor conditions and whether rooms stay comfortable.
4. Do not compromise hot water: cylinder temperature and hygiene controls should follow the manufacturer and installer instructions.
5. Ask for help if comfort is poor: persistent cold rooms can point to emitter, balancing, control or design issues, not just a flow-temperature setting.

Do not alter installer-protected commissioning parameters or safety settings without professional guidance. If you are unsure which control to change, ask the company that commissioned the system.

Questions to ask your installer

• What flow temperature and outdoor design conditions was the system designed around?
• Does the design use weather compensation, and what should the heating curve do?
• Have each room’s heat loss and radiator output been checked at the proposed temperature?
• Which controls can I adjust myself, and which settings should remain as commissioned?
• What should I do if a room is too warm or too cold after the system has had time to settle?

Compare the complete design rather than a single temperature number. You can also read about heat pump electricity use and running costs and use our sizing guide for an initial overview. Room BTU estimates are for air conditioning; whole-home heat-pump sizing requires a proper heat-loss assessment.

Frequently asked questions

← Back to all guides