The most economical way to run air source heat pump comes down to three habits: keep the flow temperature as low as your comfort allows, make sure the heating curve is set correctly, and run the system steadily instead of switching it on and off. The Energy Saving Trust’s guidance is blunt on this point: keeping a steady temperature, running your heat pump for longer periods and lowering flow temperatures can improve efficiency and reduce costs. Get those three right and most of the running-cost battle is won before you spend another penny.

The short answer

Run your air source heat pump at the lowest flow temperature that keeps your home comfortable, check that the weather compensation heating curve is set correctly rather than left on the installer’s cautious default, and keep the system on with a small overnight and daytime set-back instead of turning it off between heating bursts. Time your hot water for the cheapest part of the day, drop the legionella protection cycle to weekly if it is running daily, and pair the system with a time-of-use electricity tariff, ideally alongside solar panels and a home battery. Every one of these steps is recommended by the Energy Saving Trust, and none of them requires new hardware to start.

Turn the flow temperature down, one degree at a time

Flow temperature, the temperature of the water leaving your heat pump for the radiators or underfloor heating, is the single biggest lever on running costs. A heat pump works by moving heat rather than making it, and the smaller the lift between the cold outdoor air and the warm water it must produce, the less electricity each unit of heat costs. The Energy Saving Trust says lowering the flow temperature will have a big impact on your running costs, and suggests a practical method: turn it down in one-degree increments through the winter until the house feels too cold, then put it back up one degree to stay comfortable.

There is a trade-off to know about. Lower flow temperatures mean the heating reacts more slowly, so the house takes longer to warm up on a cold morning. That is precisely why the steady-running habit in the next section matters: a heat pump sipping away at a low flow temperature all day beats one that blasts at a high temperature for two hours and then sits idle. If you have not upgraded your radiators since the heat pump went in, this is also the moment to look at them. The Trust notes that radiators sized for a boiler, which typically runs at 75°C, are often too small once the system water drops to the 45°C that is usual for heat pumps. Larger double or triple panel radiators give more surface area without taking extra wall space, and they are what lets the low flow temperature actually warm the room.

Get the heating curve right: the most economical way to run air source heat pump starts here

The heating curve, also called outdoor weather compensation, is the setting that automatically varies the flow temperature with the weather: hotter water when it is freezing outside, cooler water in mild spells. Your installer should have set it on day one, but the Energy Saving Trust warns that installers sometimes set the curve higher than necessary just to be sure the house stays warm in winter, and an incorrectly set curve can increase your running costs. It is worth checking, because the Trust says you may be able to reduce the heating curve significantly without the home feeling too cold.

Do not guess at these settings. The Trust is explicit: you should not change the weather compensation settings unless you know what you are doing, and your installer should be happy to help if the system is not running well enough. A five-minute call to the installer that set the curve too high can be worth more than any gadget. If you moved into a property with a heat pump and have no manuals, ask a certified installer to check the installation and walk you through the settings rather than experimenting blind.

Stop switching it off: use set-back instead

In the UK we are used to firing the boiler in the morning, killing it when we leave for work, and firing it again in the evening. Heat pumps punish that habit. The Energy Saving Trust points out that in Europe people keep heating on for longer and simply lower the temperature a few degrees overnight or while out, a strategy called set-back, and it is the right way to control a heat pump. Leaving the heat pump on for longer periods does not increase overall running costs, the Trust says, because the pump runs more efficiently, offsetting the longer running period.

The logic is simple: if the house temperature drops by a few degrees, the heat pump has to work much harder to warm it back up, and it does that hard work at the coldest, least efficient part of the day. Keeping it on with a lower set-back temperature avoids the expensive recovery entirely. One exception matters: try not to have the pump heating hot water or the house overnight when outdoor temperatures are at their lowest, unless you are on a time-of-use tariff that makes night-time electricity cheap. Deep cold is when the pump works hardest for every unit of heat, so shifting demand away from those hours is pure saving.

Time your hot water and tame the legionella cycle

Hot water is the quiet budget-killer in many heat pump homes, because heating a cylinder to 60°C or more is exactly the high-lift, low-efficiency work you want to minimise. The Trust’s advice is to programme hot water for the cheapest time of day, just as you would with any water heating. Then check the legionella protection cycle. UK building regulations advise that hot water cylinders, though not thermal stores, must regularly exceed 60°C to guard against legionella bacteria, and your heat pump can be set to do this daily, weekly or permanently.

Here is the part that shows up on bills: the Trust says that if your bills are high, it may be because the legionella timer is set to do this job too frequently. For most households it is safe to run the protection cycle weekly; if you are home regularly you do not need it every day. A daily blast to 60°C that nobody asked for is one of the most common reasons a heat pump bill looks wrong, and the fix is a settings change, not a new appliance.

Tariffs, solar and batteries: the multiplier

Once the system itself is running well, the price you pay per unit of electricity is the next lever. The Energy Saving Trust recommends combining the heat pump with a time-of-use tariff, which charges less outside peak times, and notes that the biggest benefit of a home battery comes when it is paired with such a tariff: the battery stores cheap or free electricity and the heat pump draws from it instead of the grid. Adding solar panels to the mix lets you store free renewable electricity to power the pump directly, cutting grid reliance further.

This is also where the overnight set-back advice from earlier pays twice. On a time-of-use tariff, the hours when electricity is cheapest are usually the small hours, which are also the coldest. Rather than heating the house then, the economical play the Trust describes is to avoid heating demand in the deep cold and let cheap-rate stored energy or daytime solar cover the pump’s steadier daytime running. If you are weighing up whether a heat pump is even the right move yet, our guide to the Boiler Upgrade Scheme grant explains the £9,000 support available for off-gas-grid homes before the March 2027 cut-off.

Fix faults fast: the silent bill inflators

Sometimes high running costs are not a settings problem but a fault problem. The Trust advises reading the manual, understanding the control screen, and never ignoring warnings: a recurring ‘heating blocked’ message can mean the pump is running at temperatures that are too high, which is both inefficient and expensive. Sludge and dirt in radiators, faulty pumps and valves can all masquerade as a heat pump problem, and the Trust recommends water treatment and a filter in the central heating system to prevent long-term damage.

One setting deserves a specific check: the heating boost, sometimes labelled heating comfort. On the coldest days the pump may genuinely need its extra heater element, and the Trust says this is normal and should not add much to running costs over a year. But the boost should only engage when the outdoor temperature is truly low enough, so check the manual and confirm the threshold. If the boost runs regularly through an ordinary winter, treat it as a symptom and call your installer: it usually means the radiators are too small or the heating curve is set wrong, both fixable causes of high bills rather than mysteries to live with.

The savings, honestly

You will notice this guide quotes no pound figures for these measures, and that is deliberate. The Energy Saving Trust publishes its efficiency guidance without attaching savings numbers to heat pump settings, because the saving depends on your home’s heat loss, your electricity tariff and how wrong the current settings are. Anyone quoting you a precise annual saving for turning down a flow temperature is guessing. What the guidance does promise, plainly, is that lower flow temperatures, a correct heating curve and steady running each have a big, direct impact on running costs. With electricity prices where they are under the October 2026 price cap, every efficiency gain lands straight on the bill.

Your economical-running checklist

Work through these in order, because each one makes the next more effective:

1. Drop the flow temperature one degree at a time until comfort just starts to suffer, then go back up one degree.
2. Have the installer check and, if needed, lower the weather compensation heating curve.
3. Switch from on-off bursts to steady running with a small set-back overnight and while out.
4. Move hot water heating to the cheapest time of day and set legionella protection to weekly.
5. Move to a time-of-use tariff, and consider solar and a battery to multiply the benefit.
6. Check radiators are sized for 45°C water, and clear any control-screen warnings promptly.

The same low-and-slow principle applies beyond heat pumps: our winter boiler flow temperature checklist shows how conventional boiler owners can shave bills with a similar one-degree-at-a-time approach.

Frequently asked questions

What is the most economical way to run an air source heat pump?

The most economical way to run air source heat pump is to keep the flow temperature as low as comfort allows, make sure the weather compensation heating curve is set correctly, and run the system steadily with a small set-back instead of switching it on and off. The Energy Saving Trust also recommends timing hot water for the cheapest part of the day, using the legionella cycle weekly rather than daily, and pairing the pump with a time-of-use tariff.

What flow temperature should an air source heat pump run at?

There is no single correct figure, because it depends on your home’s heat loss and radiators. The Energy Saving Trust notes that 45°C water temperature is usual for heat pumps, far below the 75°C a boiler typically runs at, and advises turning the flow temperature down in one-degree increments through winter until the house feels too cold, then raising it one degree. Radiators must be large enough to heat rooms at these lower temperatures.

What is weather compensation on a heat pump?

Weather compensation, also called the heating curve, automatically adjusts the heat pump’s flow temperature as the outdoor temperature changes: warmer water when it is freezing, cooler water in mild weather. The Energy Saving Trust says the installer should set it at installation, warns that an incorrect setting can increase running costs, and notes that installers sometimes set it higher than needed. Do not adjust it yourself unless you know what you are doing; ask your installer.

Should I turn my heat pump off at night?

No. The Energy Saving Trust recommends keeping the heat pump on with a lower set-back temperature overnight and while you are out, rather than turning it off. If the house cools by a few degrees, the pump must work much harder to warm it again, wiping out any saving. Avoid scheduling heating or hot water for the coldest overnight hours unless you are on a time-of-use tariff with cheap night rates.

How often should a heat pump run its legionella cycle?

Weekly is enough for most households. UK building regulations advise that hot water cylinders must regularly exceed 60°C to protect against legionella bacteria, but the Energy Saving Trust says that if your bills are high, the timer may be set to do this too frequently, and for most people a weekly cycle is safe. If you are home regularly, you do not need it daily.

Why are my heat pump running costs so high?

The most common causes are a flow temperature set too high, a weather compensation curve left on the installer’s cautious default, on-off switching instead of steady running, a daily legionella cycle, and an electricity tariff that charges peak rates all day. The Energy Saving Trust also flags control-screen warnings such as ‘heating blocked’, sludge in radiators, and a heating boost that engages too often as signs something needs an installer’s attention.

Sources

• Energy Saving Trust, “The most efficient way to run a heat pump” (updated 19 May 2026): energysavingtrust.org.uk/how-to-ensure-a-heat-pump-runs-efficiently
• Energy Saving Trust, “Your heat pump questions answered by our experts”: energysavingtrust.org.uk/heat-pump-questions-answered (hot water timing guidance)