Heat pump winter settings: the one thing to change and five to leave alone

Quick answer: Almost nothing. A well-commissioned heat pump needs one seasonal tweak at most: nudge the weather compensation curve up a step if rooms run cool, then leave it alone. Don’t turn it off at night and don’t touch boost. Field data puts real-world efficiency at about 2.44 even on the coldest days, and it gets there by running low and steady.

Every November, heat pump forums fill up with the same question: what should I change now it’s cold? The honest answer annoys people who like fiddling. A heat pump that was set up properly in summer mostly needs you to stop helping.

The one adjustment worth making

Most heat pumps run weather compensation: the colder it is outside, the warmer the water sent to your radiators. That relationship is the curve, and it’s the only setting that should move with the seasons.

If rooms don’t quite reach temperature during the first proper cold spell, raise the curve by one step (on many controllers that’s a single number, or a degree or two on the flow temperature at the design point). Then wait 24 hours before judging it. Heat pumps heat homes slowly by design, and chasing the temperature hour by hour tells you nothing. If rooms overshoot and the house feels stuffy, come down a step. That’s the entire seasonal ritual.

Flow temperature is the efficiency lever, which is why it deserves respect: the lower the water temperature that still heats your home, the cheaper every hour of running. We’ve gone deeper on this in our guide to heat pump flow temperatures and radiators.

Five things to leave alone

Cold snap behaviour that looks wrong but isn’t

Steam pouring off the outdoor unit on a frosty morning is a defrost cycle. The unit is melting ice off its coils, and a puddle underneath it is the result. Normal. Radiators going briefly cool during defrost is normal too.

The unit running for hours without stopping in freezing weather? Also normal, and it’s the efficient way to do it. Energy Systems Catapult’s Electrification of Heat trial, which monitored hundreds of heat pumps in real UK homes, measured a median seasonal performance factor of 2.80, with a median efficiency of 2.44 on the coldest days of the year, when daily averages fell as low as -6°C. Those numbers come from machines left to run steadily. We’ve pulled the northern England data apart in our cold weather performance article, and the pattern is consistent: heat pumps cope with UK winters fine when nobody panics.

At the current 26.32p/kWh cap rate, an efficiency of 2.44 means your coldest-day heat costs about 10.7p per kWh delivered. Mild-weather heat costs less. Turning the system off and on to save money usually moves your running hours into the expensive end of that range.

Thermostat and setback

Keep the room thermostat boring. Pick a temperature you actually live at and leave it, day and night, or use a small setback of one or two degrees overnight at most. Deep setbacks that suit gas boilers punish heat pumps, because recovery demands high flow temperatures. Our thermostat settings guide covers what to aim for room by room.

The ten-minute pre-winter check

1. Clear leaves and debris from around the outdoor unit. It needs to breathe.
2. Check the condensate and defrost water can drain away somewhere it won’t freeze into a sheet of ice.
3. If your system has an external pipe that’s frozen before, lag it. Our sister problem, the boiler version, is covered in our frozen condensate pipe guide.
4. Find last winter’s settings if your installer left a commissioning sheet. That’s your baseline, not the factory default.
5. Open any TRVs you shut in spring.

If you’re still weighing up whether one of these units belongs on your wall, our air source heat pump guide covers costs and sizing, and the calculator will give you a modelled running cost for your own house.

One more winter job: the tariff

Winter is when a heat pump earns or wastes the most, because that’s when it draws the most electricity. If you’re paying the standard 26.32p/kWh cap rate for every unit, it’s worth checking whether a time-of-use or heat pump tariff suits your household; shifting hot water heating into cheap hours is easy, and some tariffs price overnight units at a fraction of the day rate. Our off-peak tariffs explainer covers how the multi-rate setups work. But don’t contort the heating schedule around cheap hours so hard that the house goes cold. The tariff should serve the comfort, not the reverse.

FAQs

Should I turn my heat pump off at night in winter?

No. Leave it running with the same or slightly reduced target temperature. The overnight saving is small and the morning recovery is expensive, so most homes come out level or worse.

Why is my heat pump steaming?

That’s a defrost cycle melting ice off the outdoor coil. It’s routine in cold, humid weather. Worry only if the unit ices up solid and stays that way.

What flow temperature should a heat pump run at in winter?

As low as still heats your home, which is the point of weather compensation. Many well-designed UK systems sit between 35°C and 45°C even in cold weather. If yours needs 55°C to cope, the radiators or the setup deserve a look.