Is it cheaper to leave the heating on low all day? Boilers and heat pumps (UK)

It depends on what heats your home. With a gas boiler, a timer usually costs less than leaving the heating on all day, though often by less than people think. With a heat pump, it’s usually the other way round: leave it running, a couple of degrees lower at night or when you’re out.

This guide follows the HanaHow episode: why heat loss decides it, where the boiler myth comes from, what changes with a heat pump, and the settings to try. The calculator compares the two for your own home at the current price cap rates.

The short answer

• Gas boiler: use a timer. The Energy Saving Trust’s answer to “Is it better to leave the heating on all day rather than turning it off and on?” is “If you have a boiler, then no. Keeping your heating on all the time will use more energy and cost you more money.” In a very well insulated home it’s close to a tie.
• Heat pump: keep it on, with a small set-back. The Energy Saving Trust says that “if you have a heat pump, then you can save money by leaving the heating on all day”, and Heat Geek suggests a set-back of two or three degrees.
• Electric heaters (panel heaters, fan heaters, oil-filled radiators): a timer always uses less, because they turn each unit of electricity into one unit of heat however you run them. Storage heaters on a night tariff are a different case.

Why the timer usually wins with a boiler

A house leaks heat all the time, through the walls, roof, windows, floor and every draught. How fast depends on the gap between the inside and outside temperature. At 20°C inside and 5°C outside, the gap is 15 degrees. Let the house drift down to 15°C while you’re out and the gap is 10 degrees, so it leaks about a third less heat for as long as it stays cooler.

That’s the whole argument. A house kept at 20°C all day leaks at the full rate all day. A house on a timer spends part of the day cooler, leaking less, and the boiler only has to replace what leaked out.

Warming it back up doesn’t cost more than you saved

The usual worry is that warming a cold house back up uses more than you saved by switching off. It doesn’t, at least in heat. The boiler puts back the heat that leaked out while the heating was off, and a cooler house leaked less of it than a warm one would have. Roger Bisby of Skill Builder puts it simply: “no, it’s not cheaper to leave your heating on all the time.”

Turning the thermostat up higher won’t warm the house any faster on most systems, either. The Energy Saving Trust: “turning up your room thermostat won’t make your home heat any faster!” It just means the heating stays on longer once you’re warm.

The boiler efficiency catch

Heat isn’t quite the same as gas, as Heat Geek points out. Modern condensing boilers are more efficient with cooler water, because they recover extra heat from the steam in their exhaust when the water coming back is cool enough. Running low and slow, with the flow temperature turned down, can make a boiler a few per cent more efficient than heating up hard twice a day. Heat Geek’s example compares the same boiler at 85% and 93%.

That doesn’t apply if the boiler’s flow temperature dial is left high: low and slow then just means more switching on and off. The Energy Saving Trust has a guide to lowering your boiler’s flow temperature.

What our model found

We built a simple model of a home on a 5°C day: a typical semi, kept at 20°C all day, against a timer on from 06:30 to 08:30 and 17:00 to 23:00 that comes on early enough to be warm by those times. We assumed the boiler is 92% efficient running all day and 88% on the timer, which favours heating all day. These are costs just for the heating, at the price cap’s gas rate, with no standing charge, hot water or the free heat from people, cooking and the sun.

Home	All day at 20°C	On a timer	Difference
Typical semi	£4.68 a day	£4.53 a day	Timer 3% cheaper
Leaky or draughty	£7.80 a day	£7.22 a day	Timer 7% cheaper
Very well insulated	£2.49 a day	£2.51 a day	About a tie

With the same 90% efficiency both ways, the typical semi’s timer saving is 7%. The model treats the whole house as one lump, which makes it slow to warm up, so it starts the heating about two hours early. Real rooms warm faster than that, and a model where the air warms faster than the walls would probably show bigger timer savings. So take the pounds as an illustration: the solid part is the direction. With a boiler, a timer is cheaper or level, and the gap grows in leakier homes.

Put in your own home, hours and temperatures:

“Low all day” also only feels cheap because low means a cooler house. In the same typical semi, all day at 18°C costs about £4.05 a day, less than the 20°C timer. The saving there comes from the lower temperature, not from leaving it on.

Insulated and leaky homes

A well insulated home loses heat slowly, so it barely cools down while the heating’s off. There’s little for a timer to save, and the boiler’s small efficiency gain from steady running can cancel it out. That’s why it comes out about even.

A leaky or draughty home cools quickly, so it spends more of the off hours at a lower temperature and the timer saves more. Heavy walls that hold heat for a long time behave more like the insulated home. A modern timber-frame house, Roger Bisby notes, heats up very quickly but loses it quickly too.

How you live matters too. If someone’s home all day, a timer has fewer hours to save on, and the answer drifts towards steady heating. Heat Geek’s point is that it isn’t a simple yes or no: it’s how long the heating is off, and how far you let the house drop when it is.

Heat pumps: leave it on, a little lower at night

Heat pumps turn the answer round. The Energy Saving Trust says they can give three to four units of heat for every unit of electricity, and they do best when they run cool. It gives about 45°C as the usual water temperature for a heat pump, against about 75°C for a typical boiler.

Warming a cold house back up quickly needs hotter water, and a heat pump makes less heat from each unit of electricity when it runs hotter. A heat pump also has much less output than a boiler, so it can take hours to warm a house that’s cooled down, sometimes with an electric boost heater helping, which makes one unit of heat per unit of electricity. Heat Geek’s example is a heat pump at about 200% when it’s run hot and switched on and off, against about 500% run low and slow.

So the Energy Saving Trust says: “it’s best to keep your heat pump on all the time, and let your ‘set-back’ maintain a lower temperature when you’re out or asleep.” A set-back is a lower temperature the heating holds instead of switching off. Heat Geek’s advice: “if you have a heat pump what you’ll generally find is in most scenarios is that you want a two or three degree setback and to heat all day most of the time.”

In our model’s typical semi with a heat pump, heating all day at 20°C cost about £3.83 a day. The calculator warms a heat pump up gently, as a weather-compensated controller would, with the water a few degrees hotter than it needs to hold 20°C, starting early enough to be warm by 06:30 and 17:00. That came out about level, at £3.88 on a timer, and the same with a 2 or 3 degree set-back, because the house barely cooled before the heating came back on. In a leaky home the timer came out a little cheaper, and in a very well insulated one a little dearer, all within about 3%. Without the early start, the timer looked much cheaper only because the house never got back to 20°C.

The model can’t show one reason set-backs help a heat pump. It keeps the outside temperature the same day and night, but the Energy Saving Trust points out that the air can be 5°C or more colder overnight, which makes a heat pump less efficient, so a lower temperature at night saves it working hardest when it’s least efficient. The model’s heat pump also averages a COP of about 3.7 holding 20°C on a 5°C day, with no allowance for defrosting; real systems often average a little lower.

What a unit of heat costs at the price cap

Ofgem’s price cap from 1 October to 31 December 2026, the average for Direct Debit in England, Scotland and Wales, is:

	Unit rate	Standing charge
Gas	7.97p per kWh	29.68p a day
Electricity	26.32p per kWh	54.83p a day

Gas includes 5% VAT, and there’s no VAT on electricity from 1 October 2026 to 31 March 2027. Your own rates depend on your region and tariff. The standing charge is the same whether you use a timer or leave it on, so it doesn’t change which way is cheaper.

What matters is what you pay for each unit of heat, after the boiler’s efficiency or the heat pump’s COP (coefficient of performance: units of heat per unit of electricity):

Heating	Pence per kWh of heat
Gas boiler at 90%	8.9p (7.97 ÷ 0.9)
Heat pump at a COP of 4	6.6p (26.32 ÷ 4)
Heat pump at a COP of 3	8.8p (26.32 ÷ 3)
Heat pump at a COP of 2.5	10.5p (26.32 ÷ 2.5)
Electric heater	26.3p

A heat pump run hot, at a COP of 2.5, makes heat that costs more than gas. Run cool, at 4, it’s well under. That’s why the way you run it matters so much more than with a boiler. Some heat pump owners also use a time-of-use tariff with cheaper electricity at certain hours, which the Energy Saving Trust says can cut costs further; the calculator uses one flat rate.

Northern Ireland isn’t covered by Ofgem’s price cap or by the VAT cut on electricity. Its regulated tariffs are reviewed by the Utility Regulator, and prices differ, so put the unit rates from your own bill into the calculator. The maths works the same way.

Weather compensation

Weather compensation turns the water temperature down on milder days, using an outdoor sensor. It helps both kinds of heating: a boiler spends more time cool enough to condense, and a heat pump stays efficient. The Energy Saving Trust describes it as a control that “automatically measures the outside temperature and adjusts the boiler thermostat temperature as needed”.

Heat pumps nearly always have it, set as a “heating curve” by the installer. The Energy Saving Trust says installers sometimes set the curve higher than needed, so it’s worth turning it down a degree at a time through the winter until the house feels too cold, then back up one. Many boilers can add it with an outdoor sensor, and some smart thermostats do a similar job by adjusting the boiler’s flow temperature.

Damp, mould and set-backs

A house that gets too cold is more prone to damp, because cold walls and windows collect condensation. The Energy Saving Trust says “Rooms where the heating is turned off or low during colder months are prone to damp problems”, but also that “leaving heating on all the time just to avoid damp isn’t a sensible solution.” Our condensation and black mould guide explains why it collects where it does.

So if your home is prone to damp, keep the timer but set the off hours to a set-back rather than off, say 16°C. In our typical semi a 16°C set-back cost nothing extra, because the house never fell that far on a 5°C day. In the leaky home it cost about 5p a day more. Better ventilation, such as running the extractor fan and opening the trickle vents, is the first fix for condensation.

Don’t let it get too cold for your health, either. UKHSA’s winter advice for England is to heat the rooms you spend a lot of time in, such as the living room or bedroom, to at least 18°C, which matters most for older people and anyone with a health condition.

Frost protection

Pipes and tanks can freeze in a very cold spell if the house gets cold enough. Most newer boilers have a built-in frost thermostat that fires the boiler or runs the pump when it gets very cold, but Tomkat Gas Training points out that this protects the boiler, not the pipes around the house. So if you’re going away in a cold spell, leave the heating on at a low set-back rather than switched off, and keep frost-prone pipes in lofts and garages lagged.

Settings to try

Gas boiler

1. Use the timer. The Energy Saving Trust suggests having it come on about half an hour before you get up and go off about half an hour before you go to bed.
2. Turn the thermostat to the lowest comfortable temperature, usually between 18 and 21°C. Going from 22 to 21°C could save about £120 a year in Great Britain and £80 in Northern Ireland, according to the Energy Saving Trust.
3. Turn the flow temperature down, so the boiler condenses more of the time.
4. On cold nights, or in a damp-prone home, use a set-back rather than off, if your thermostat has one.
5. Leave the thermostat alone when you get in. Turning it up won’t warm the house faster.

Heat pump

1. Leave it on, with a set-back of two or three degrees at night or when you’re out.
2. Check the heating curve isn’t set higher than you need.
3. Avoid big swings, such as switching off all day and expecting it to catch up in an hour.
4. If the boost heater comes on often, ask your installer to check the radiators and the heating curve, as the Energy Saving Trust suggests.

Electric heaters

Heat only the rooms you use, when you use them. A timer or thermostat on each heater saves more than leaving them on.

Either way, every degree lower saves money, and a jumper is still very good value.

Sources

• Ofgem: Energy price cap unit rates and standing charges, 1 October to 31 December 2026. HM Revenue and Customs: Revenue and Customs Brief 10 (2026), on the temporary zero rate of VAT for household electricity in Great Britain. Utility Regulator, Northern Ireland.
• Energy Saving Trust: When should I put my heating on?, The most economical ways to use your central heating, The most efficient way to run a heat pump, In-depth guide to heat pumps, Heating controls and How to get rid of damp.
• Heat Geek: Is it better to leave the heating on constantly? Boilers and heat pumps, 3 March 2022. Skill Builder, Roger Bisby: Is it cheaper to leave your heating on constantly?. Tomkat Gas Training: Is it cheaper to leave your heating on 24/7, true or myth, on set-backs and frost thermostats.
• UK Health Security Agency: Keeping warm and well: staying safe in cold weather, for England, updated 28 April 2026.
• Our model: a one-zone house stepped minute by minute over a settled day, typical semi losing 150 W per degree and holding 3.75 kWh per degree, leaky 250 W and 3.0 kWh, well insulated 80 W and 4.8 kWh. The assumptions are listed under the calculator.