Weather compensation
A control strategy that varies flow temperature according to outdoor temperature so the system delivers only the heat the building currently needs. It is standard on European heat-pump installations and materially affects running cost.
Also called load compensation, outdoor reset
What is weather compensation?
Weather compensation varies the flow temperature according to outdoor temperature, so the system sends hotter water only when it is genuinely colder outside. In North America it is called outdoor reset.
Weather compensation: how it works
Heat loss from a building rises roughly in proportion to how much colder it is outside, so the water temperature needed to replace that loss rises with it. A heating curve maps one to the other. The system then runs continuously at a low flow temperature in mild weather and raises it only as conditions demand, which keeps the heat pump working at the smallest lift it can.
Where you meet the term
- On a heat pump controller, as a heating curve with a slope and an offset.
- In a running cost investigation, where a fixed flow temperature set at commissioning explains costs a correctly sized system should not have.
- In a comfort complaint, where a curve set too low leaves the house short on the coldest days.
How to check it
- Confirm the outdoor sensor is reading sensibly. A sensor in direct sun, or one that has failed to a fixed value, feeds the curve the wrong input and the whole strategy follows it. Technician
- Adjust the curve one step at a time across a cold spell. Lowering the slope reduces flow temperature at low outdoor temperatures. Changing it repeatedly within a day tells you nothing, because the building responds slowly. Technician
Weather compensation: what it is not
- Weather compensation is not a thermostat replacement. It sets how hot the water is, while room controls still decide when heat is called for.
- A curve set too aggressively low saves nothing if the occupants respond by raising the room set point or switching on other heating.
Weather compensation questions
Is weather compensation the same as outdoor reset?
Yes. They are the same strategy under different regional names, and both work by mapping outdoor temperature to a target flow temperature through a curve.
Why does my heat pump run constantly with it enabled?
That is the intended behaviour. Long low-output runs at a low flow temperature are more efficient than short bursts at a high one, and they hold the building steadier.
How do I know if my curve is set correctly?
The house should hold temperature in cold weather without needing help, and the flow temperature should be visibly lower in mild weather. Needing to raise the room set point on cold days suggests the curve is too shallow.
Where this definition comes from
Written from government guidance material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- Energy label and ecodesignThe European framework behind SCOP, seasonal space heating efficiency, and the product energy label.