What temperature should I set my thermostat to?

The second number that matters is the hot water cylinder. Stored water should sit at 60°C or above, with the Energy Saving Trust giving a range of 60 to 65°C for the hot water thermostat¹. That is a hygiene requirement as much as a comfort one, and it is separate from the room thermostat setting.

The third is the setback floor. A programmable thermostat can be given a minimum temperature the home should not drop below, and 16°C overnight or when the house is empty is the example the Energy Saving Trust gives¹. Below that, the picture changes: the NHS advises at least 18°C for health, and not below 16°C for older people or those with impaired mobility⁵.

Recommended thermostat temperature: 18 to 21°C

The 18 to 21°C band is repeated across official, independent and supplier guidance, which is unusual for a heating figure. The Energy Saving Trust frames it as the lowest comfortable temperature rather than a target, and the same wording appears in its Christmas energy saving tips and its take control of your heating page¹. Cadent Gas gives 18 to 21°C as the setting that keeps a household safe and well⁴. Consumer guides from Which? and ivie give the same range, with ivie describing it as the ideal comfort and efficiency zone for healthy adults⁸.

What drives the range rather than a single number is that comfort is personal and depends on age, health, activity and clothing. The lower end suits a healthy adult in a reasonably insulated home; the upper end suits households with babies, older people or anyone who feels the cold. Fuel poverty definitions use 21°C in the living room and 18°C in other rooms for households that do not need an enhanced heating regime, which shows how the two ends of the band map onto different rooms¹⁰.

In practice, the setting is a ceiling on the heating system, not a promise. A room thermostat turns the heating on until the room reaches the chosen temperature and then switches it off, so the figure only holds if the radiators and boiler can actually deliver that heat¹. Where the home is cold and draughty, raising the thermostat does not fix the cause.

For energy independence, the thermostat is the one control a household can change without touching the boiler, the supplier or the fuel. It sets how much gas or electricity the home draws, and it works the same whether the heat comes from a gas boiler, a heat pump or storage heaters. What it cannot do is reduce dependence on the fuel itself: a lower setting cuts consumption, not the connection.

Finding your lowest comfortable temperature, one degree at a time

The practical method in the guidance is to start at a comfortable setting and reduce it one degree at a time, rather than jumping to a figure. The Energy Saving Trust's approach is to set the thermostat to the lowest temperature the household is comfortable at, which for most people falls in the 18 to 21°C band¹. Smart Energy GB makes the same point for renters, noting that reducing the thermostat by one degree can lower bills without sacrificing comfort¹¹.

The size of the saving per degree varies between sources. ivie gives 4 to 8 per cent of the heating bill for every degree the thermostat is lowered⁹. OFTEC gives 10 per cent per 1° reduction, and the Welsh Government gives up to 10 per cent on heating bills for a 1°C reduction¹². The Energy Saving Trust's rented homes guidance gives 10 per cent for a one degree turn down on a wet central heating system¹⁴. The spread reflects different assumptions about how long the heating runs and what fuel is used, so the honest reading is that a degree is worth somewhere between 4 and 10 per cent, with most sources clustering at the top of that range.

One degree at a time also protects against overshooting. Dropping straight to 16°C in a home that has been run at 21°C tends to produce a cold house, a household that turns the heating back up, and no saving at all. The stepwise approach lets the household find the point where comfort holds, which is the only setting that will be kept.

Hot water: cylinder and hot water thermostat settings at 60 to 65°C

Hot water is a separate control from the room thermostat, and the figures are different. The Energy Saving Trust gives 60 to 65°C for the hot water thermostat¹. Age UK gives 60°C as fine for most people¹⁵, and Confused.com gives 60°C as the setting that cuts bills⁷. Citizens Advice states the reason plainly: the cylinder thermostat should be set high enough, at least 60 degrees Celsius, to control bacteria in stored water¹⁶.

Which? adds a practical condition: where a home has a hot water cylinder that stores water, the settings need to be set by a boiler engineer and kept hot enough to avoid the build-up of bacteria in the storage tank¹⁷. That is a job for someone with the tools and the training, not a dial to be turned on a whim.

Solar water heating is the exception in the figures. OFTEC's guide to solar water heating gives a cylinder thermostat setting of 55 to 60°C, described as the usual setting, because the cylinder thermostat is regulating a different heat source and the solar circuit has its own controls¹⁸. That is lower than the 60 to 65°C given for a conventional cylinder, and the two figures should not be mixed.

For independence, the cylinder thermostat is a local control with no cloud dependency. It sits on the tank, it works when the broadband is down, and it does not care which supplier provides the gas. The dependence it leaves is on the boiler or heat source that heats the cylinder, and on the engineer who sets it correctly.

Setback temperatures: how low is too low

A setback temperature is a floor, not a target. The Energy Saving Trust describes it as a minimum temperature the home should not drop below, giving 16°C overnight or when the house is empty as the example¹. That is the figure most commonly quoted, and it is the one to treat with care.

The health guidance is firmer than the energy guidance. The NHS recommends heating the home to at least 18°C, and not below 16°C for older people or those with impaired mobility⁵. Smart Energy GB repeats the NHS advice to keep the home at least 18°C for health¹⁹. The Centre for Sustainable Energy's advice for renters is more specific still: households with health concerns, older people or small children should not go below 18°C²⁰. So 16°C is a floor for healthy adults, not a general minimum.

Homes without frost protection need a different setting entirely. Home Energy Scotland advises setting the heating thermostat to 10°C and switching on the programmer, or setting it to 24 hours, to achieve a similar effect²¹. That is a frost setting, not a comfort one, and it exists to stop pipes freezing rather than to keep anyone warm.

Heat pumps behave differently again. ClimateXchange's work on Scottish housing retrofit describes constant running with minimal setback, for example to 18°C, as the pattern that delivers comfortable conditions in solid wall homes with radiator upgrades²². Storage heaters have their own version: some models have a setback temperature, which is the temperature the heater will try to keep the room at while it is set to heating off²³.

The conflict in the guidance is worth stating. One line of advice gives 16°C as the minimum setback; another gives a setback two or three degrees below the comfortable temperature. The two produce different numbers for a home running at 21°C, and the documents do not resolve it. A household choosing between them is choosing between a fixed floor and a relative one.

Where the thermostat is placed matters as much as the setting

A thermostat measures the air where it is mounted, not the air in the room the household is sitting in. USwitch's guidance on smart thermostats is to place them where the temperature is relatively consistent²⁴. Smart Energy GB's placement advice is more detailed: the thermostat should not be blocked by furniture or curtains, should be kept away from heat sources such as electric fires or heaters, should be protected from draughts, and should be placed away from draught sources such as windows or the front door²⁵.

The most common placement error is a thermostat in a room that is heated separately. USwitch's guidance on heating one room rather than the whole house states that the thermostat should not be in the room with the additional heating, because it will disrupt control, and that a wireless thermostat should be moved out of the locally heated room²⁶. A thermostat sitting next to a log burner or a portable heater will read warm air, switch the rest of the house off, and leave every other room cold.

Hallways and landings are common mounting points and are often the worst. A hallway with a front door, a draught and no radiator behaves nothing like a living room, so the setting that keeps the hall at 20°C may leave the living room at 17°C. This is where zoning and thermostatic radiator valves do work a single thermostat cannot, and where a room thermostat sited properly earns its place.

Placement also decides how much of the home's independence the control actually delivers. A well-sited thermostat responds to the house; a badly sited one responds to the hallway, and the household compensates by raising the setting, which costs money without improving comfort.

Thermostat settings and household energy bills

The bill figures for thermostat reduction are consistent in direction and inconsistent in size. The Energy Saving Trust's rented homes guidance gives 10 per cent on bills for a one degree turn down on a wet central heating system¹⁴. Northern Ireland's nidirect guidance gives as much as 10 per cent on heating bills for a one degree Celsius reduction²⁷. Confused.com gives £90 off heating costs for a one degree reduction²⁸, and its energy efficiency guide repeats £90 per year²⁹. USwitch gives as much as £90 per year for a single degree³⁰.

Two figures sit well outside that cluster. East Herts Council's grants and advice page states that reducing the thermostat by 1° could save up to 25 per cent of heating bills and associated carbon³¹. The Chartered Institute of Plumbing and Heating Engineering gives a further 7 per cent saving from turning the thermostat down to 18°C³². The 25 per cent figure is far above every other source and should be treated as an outlier rather than a planning assumption.

The cash figures also depend on the starting bill, which the sources do not fix. A £90 saving is a larger share of a small bill than a large one, and the percentage figures and the cash figures are not directly comparable. What the sources agree on is that the saving is real, that it scales with how much the heating runs, and that it is largest in homes that were previously run warm.

For a household's energy independence, the thermostat is the cheapest lever available: no installation, no subscription, no app, no supplier. It reduces the volume of fuel the home draws, which matters most where the fuel is bought at a variable price or delivered off the gas grid. It does not change where the fuel comes from, and it does not remove the standing charge or the connection. The heating controls pillar sets out how the thermostat sits alongside programmers, TRVs and zoning in the wider control system.