What Temperature to Set the Thermostat and Each Room

A room thermostat does one job: it turns your boiler on and off automatically when the room temperature reaches the level you have chosen¹. It is a switch with a thermometer in it, not a dial that makes the radiators hotter or colder. Set it to 20°C and the heating runs until the room reaches 20°C, then stops, then starts again when the room cools. Everything else about heating controls, timers, programmers, radiator valves, builds around that simple on-off behaviour.

The number you choose matters more than most people expect. UK guidance is remarkably consistent: set your thermostat to the lowest comfortable temperature, which for most people is between 18°C and 21°C². Dropping that setting by a single degree, from 22°C to 21°C, is widely quoted as saving around £120 a year in Great Britain and £80 in Northern Ireland³. This page sets out what each setting does, what each room needs, and where the thermostat itself should sit so it reads the house honestly.

How your thermostat works

The thermostat is the part of your heating system that decides when the work is done. It senses the air temperature where it is mounted and switches the boiler off once that air reaches the level you chose, then switches it back on when the room cools below it¹. It does not decide how hot the radiators get and it does not decide when the heating comes on each day: those are separate jobs, done by the boiler's own control and by the timer or programmer.

The distinction matters because homes have several "thermostats" doing different things. The thermostat on the boiler itself controls the temperature of the water flowing through the heating system, not the temperature inside your rooms⁷. A room thermostat, the wall-mounted unit most people mean when they talk about "the thermostat", controls the rooms. A wireless room thermostat sends a signal to a receiver connected to the boiler, which tells the boiler when to turn the heating on or off, without a wired connection between the two⁸. A smart thermostat does the same switching job but adds programming, app control and automation on top⁹.

Electric storage heaters work the same way in principle: each heater has its own thermostat that lets you set the temperature you want it to heat the room to¹⁰. The consequence of the thermostat being a simple switch is that its position in the house is as important as the number on its display. If the controls around it are not set correctly, adjusting anything else may not give the results you expect⁹. The rest of this page is about choosing the number, and then making sure the thermostat can actually see the temperature you are trying to control. For the wider picture of how all these controls fit together, see our guide to heating controls.

Ideal temperatures range from 18°C to 21°C

Nearly every UK energy advice body lands on the same range. Energy Saving Trust's guidance is to set your thermostat to the lowest comfortable temperature, which for most people is between 18°C and 21°C². British Gas Energy Trust says the same: set your main room thermostat somewhere between 18°C and 21°C, a temperature comfortable for most people¹¹. Cadent, the gas network, puts it as a safety point as well as a comfort one: to help keep you safe and well, your thermostat should be set between 18 and 21°C¹².

The range repeats across independent sources. Energy Saving Trust's seasonal advice says between 18°C and 21°C is suitable for most people to be comfortable¹³. Ivie, a heating controls maker, notes that for healthy adults a setting between 18°C and 21°C is often cited as the ideal comfort and efficiency zone¹⁴. Smart Energy GB reports that in most households central heating thermostats are typically set between 18 and 21°C¹⁵, so if yours is in that band you are in line with the national norm. British Gas Energy Trust's research-backed tips simply say to set your thermostat between 18°C and 21°C for comfort and efficiency¹⁶.

Two things sit behind the "lowest comfortable" wording. First, health: Cadent's damp and mould guidance also points to 18 to 21°C, because cooler, humid homes are where mould grows¹⁷, and the NHS advises keeping regularly used rooms at least 18°C, especially where someone in the household is vulnerable¹⁵. Second, money: every degree above what you need is heating you are paying for without feeling any warmer. The World Health Organisation figure quoted in consumer guidance is that healthy adults can go as low as 18°C¹⁸. Which? summarises the same evidence as 18 to 21°C being the ideal temperature range in cold weather¹⁹. Where you settle within the band is a matter of comfort, but the band itself is well established.

What one degree is worth

The most widely quoted figure comes from Energy Saving Trust: turning down your thermostat from 22°C to 21°C can save £120 a year in GB and £80 in NI on energy bills³. The same figure appears in Energy Saving Trust's advice on when to put the heating on, £120 a year in Great Britain and £80 in Northern Ireland²⁰, in its guidance for renters²¹, and in its advice on improving an EPC rating, which puts it at around £120 a year in GB or £80 in NI²².

Other estimates sit in the same territory without matching exactly. Confused.com's energy saving tips put a one-degree reduction at up to £90 a year¹⁸. Which? reports the Energy Saving Trust estimate that turning the thermostat up by just one degree costs an additional £90 a year in heating²³, the same figure seen from the other direction. Northern Gas Networks says turning your temperature down by just one degree can save up to a hundred pounds every year²⁴. Official guidance in Northern Ireland and the nidirect equivalent both say turning the thermostat down by just one degree Celsius could save as much as 10 per cent on heating bills²⁵, and Which? reports the Energy Saving Trust estimate of about 10% from turning down the main thermostat by one degree¹⁹. Ivie's guidance gives a percentage range instead: for every degree you lower your thermostat, you can typically save between 4% and 8% on your heating bill¹⁴.

These figures differ because they are estimates built on typical homes, typical weather and a snapshot of energy prices, and they move when prices move. The £120 and £80 figures are the most commonly cited and the most recent, so they are the ones to work from, but treat any of them as an indication of scale rather than a promise. The direction, however, is not in dispute: one degree is worth roughly a hundred pounds a year to a typical household, and the saving is repeated for each further degree you can comfortably do without.

Settings for day, night and holidays

The 18°C to 21°C band is a daytime, occupied-house setting. What happens the rest of the time is where a thermostat earns its keep, and the pattern is usually built from three ideas: a comfort setting when you are home and awake, a lower setting overnight and when the house is empty, and a floor setting that protects the building.

For time away from home in freezing weather, OFTEC's winter advice is to leave the temperature set between 12 and 15 degrees to avoid the risk of burst pipes⁵. That is a setback, not an off switch: the heating still runs if the house gets genuinely cold, but it is not keeping empty rooms at daytime comfort. For homes without frost protection on the system, Home Energy Scotland's winter guidance goes further: set your heating thermostat to 10°C and switch on the programmer, or set it to 24 hours to achieve a similar effect⁶. The point of the floor setting is that the boiler can still fire if the fabric of the house, and the water in its pipes, approaches freezing.

Overnight, the same logic applies with a comfort twist: bedrooms are better slept in when they are cooler, which is covered in the next section. A programmable thermostat or a smart thermostat handles the transitions automatically. Most smart thermostats allow you to programme in multiple routines, so that your home is always at your desired temperature at the times you choose²⁷. A trial reported in consumer guidance suggests a way to find your own floor: set the thermostat to 18 to 19°C and leave the heating on constantly for a period, then compare with your normal pattern¹⁸. The detail of building these patterns, including how setback works and whether to leave the heating on low, is covered in our page on heating schedules and setback.

Room by room: living rooms, bedrooms, bathrooms and vulnerable occupants

A single thermostat controls one thing: the temperature of the air where it sits. Rooms further from it, or with different heat losses, will differ. The guidance that exists is room-specific in only a few places, but those places are consistent.

• Living rooms and the rooms you use most: keep the room you spend most time in between 18°C and 21°C (64°F and 70°F) to avoid potential health problems²⁴. The NHS advises keeping your home, meaning the rooms regularly used such as the bedroom or living room, at least 18°C¹⁵.
• Bedrooms: Smart Energy GB's guidance on maintaining the ideal home temperature suggests 16°C to 18°C for the bedroom⁴, cooler than the daytime band, which suits sleep.
• Vulnerable occupants: the 18°C minimum is especially important for vulnerable household members, according to NHS guidance cited by Smart Energy GB¹⁵. For healthy adults, the World Health Organisation figure quoted in consumer guidance is that you can reduce it to as little as 18°C¹⁸.
• Bathrooms: no separate UK-wide temperature figure is given for bathrooms in the guidance; they are typically heated for short periods when in use, and building guidance excludes bathrooms from some radiator valve requirements²⁸.

The health floor is the firmest line on this page. Below 18°C in a room someone actually lives in, the risks shift from comfort to health, particularly for older people, young children and anyone with a cardiovascular or respiratory condition. The damp angle reinforces it: Cadent's guidance on damp and mould prevention ties the 18 to 21°C thermostat setting directly to keeping mould at bay¹⁷, because cold surfaces in cool rooms condense moisture. A house held at the low end of the comfort band with adequate ventilation is both cheaper and healthier than a house that swings between hot and cold.

Achieving different temperatures in different rooms is not the thermostat's job alone. That needs thermostatic radiator valves on the radiators, or a zoned system, both covered below. For more on the individual rooms, see our page on room temperatures.

Best thermostat placement: central spot, 1.5 metres high, clear of heat, sunlight and draughts

A thermostat can only switch the boiler honestly if it is measuring air that represents the house. Myson's installation guidance is that the ideal location is around 1.50 m high, out of sunlight and draught²⁹. Smart Energy GB adds the practical list: make sure your thermostat is not blocked by furniture or curtains, and keep it away from heat sources like electric fires or heaters, and away from draughts from windows or the front door¹⁵. Uswitch's guidance on smart thermostats makes the underlying point: the best place to put a smart thermostat is in a place where the temperature is relatively consistent³⁰.

What goes wrong when the siting is poor is easy to picture, and Ideal Heating's guide spells it out: a thermostat placed somewhere warm may mean the central heating never turns on, while one placed somewhere cool may mean the radiators never go off even when the house is well over the set temperature. Because a utility room might frequently be warmer than 20°C, you might find that the central heating never comes on³¹. The thermostat is not wrong in either case; it is faithfully reporting a room that does not represent the rest of the house.

One further rule applies to homes that heat one room separately, for example with a log burner or electric heater. Uswitch's guidance is blunt: if you do this, make sure your thermostat is not in the room with the additional heating, otherwise it will disrupt control of the rest of the house³². A wireless thermostat can simply be moved out of the locally heated room³². If your thermostat is badly sited, moving it is usually cheaper and more effective than replacing it, and the types and siting options are covered in our page on room thermostats.

How many thermostats your house should have

One thermostat gives one temperature for the whole house. That is enough for many homes, but the building rules across the UK assume more than one zone of control. Northern Ireland's Technical Booklet F1 (2022) states that central heating systems should be provided with a minimum of two independent heating zones, each controlled by a room thermostat, with thermostatic radiator valves on radiators in rooms without a thermostat, except bathrooms²⁸. Scotland's draft domestic building services compliance guidance takes the same line: dwellings with a total floor area under 150 m² should have at least two space heating zones with independent temperature control, one of which is assigned to the living area, and the same two-zone minimum applies to larger dwellings and to community heating systems with independent temperature and time control³³.

In practice, zoning means the heating can be off or set back in rooms that are not in use while the living areas stay warm. It can be done with smart thermostats and smart radiator valves, which let you set temperatures room by room from an app, or with conventional zone valves and separate thermostats. Most smart thermostats allow you to programme in multiple routines, so that your home is always at your desired temperature in each zone²⁷. The trade-offs, costs and wiring approaches are set out in our guide to heating zoning.

The energy independence angle is worth stating plainly. Zoning does not reduce your dependence on gas or electricity, it reduces waste: you heat fewer cubic metres of air to comfort temperature, so the same warmth costs less fuel. A single thermostat in a large or awkwardly laid-out house tends to overheat the rooms near it and underheat the rooms far from it, and the occupants fix that by turning the whole system up, which is the most expensive possible remedy.

Myths and mistakes: cranking it up does not heat the house faster

The most common mistake is treating the thermostat like an accelerator. It is not. Because the thermostat simply switches the boiler on until the room reaches the set temperature¹, turning it up well above the temperature you actually want does not warm the room any faster: the radiators run at exactly the same output either way. What the higher setting does is keep the boiler running long after the room has passed comfortable, which is where the £90 a year cost of one extra degree comes from²³.

The second mistake is fighting the thermostat's position rather than fixing it. If the house feels cold while the thermostat reads 20°C, the likely explanation is that the thermostat is somewhere warmer than the rooms you are sitting in, and the fix is to move it, not to raise the setting³¹. The third is impatience in the other direction: Myson's guidance for finding a comfortable setting with a programmable room thermostat is to start low, say 18°C, and then turn it up by one degree per day until your comfort level is reached²⁹. That finds the lowest comfortable setting, which is the whole point of the exercise, rather than starting high and never coming down.

A fourth mistake is adjusting one control and expecting another's results. The boiler thermostat changes the temperature of the water in the system⁷, and if the heating controls are not set correctly when you adjust it, you might not get the results you expected⁹. If you want to know whether the money figures on this page would actually show up in your bills, our page on whether heating controls save money sets out the evidence.

Testing thermostat accuracy and knowing when a new one is needed

A thermostat that reads wrong silently costs money in both directions: too high and the house overheats, too low and it never gets warm. Independent testing shows how the professionals check. Which? puts smart thermostats in a temperature-controlled chamber, measuring how accurately they record the temperature and how quickly the relay responds³⁴. A householder can do a rough version at home: place a separate thermometer beside the thermostat and compare readings, and watch whether the boiler actually switches off around the set temperature.

Accuracy is not the only thing that degrades. Ageing mechanical thermostats can develop a wide gap between the temperature at which they switch on and off, so the house swings between too cold and too hot. If a balance of the radiators is needed, the process itself uses the thermostat: Which?'s radiator balancing guide has you turn all the radiator thermostats to 0, then to 2, starting from the radiator furthest from the boiler²³. If the system behaves oddly during that kind of check, or the thermostat is unresponsive, replacement is the practical answer. Ivie's advice on timing is simply to look into replacing your old thermostat before it gets too cold²⁷. The fitting options and costs are covered in our guide to installing and replacing heating controls.

What thermostats, timers and water heating controls do

The last distinction to be clear about is which control does which job. The room thermostat controls the heating in response to room temperature¹. A timer lets you control when your heating or hot water turns on and off each day, so that you can programme your central heating around your routine¹. The hot water thermostat stops the cylinder becoming hotter than it needs to be: once the water reaches the set temperature, the heat supply from the boiler is turned off². Guidance says to set the temperature of the hot water thermostat between 60°C and 65°C², and Age UK's advice is that a temperature of 60°C (140°F) is fine for most people¹.

The 60°C figure has a health floor under it. Citizens Advice guidance is that the temperature on the cylinder thermostat should be set high enough, at least 60 degrees Celsius, and the temperature on the boiler at least 65 degrees Celsius³⁵. Energy Saving Trust makes the same point for conventional boilers with a hot water cylinder: make sure the temperature is no lower than 65 degrees¹³. Where a regular boiler has only one control for both radiators and hot water, that control should be set no lower than 65°C so it can heat the cylinder to 60°C². Consumer guidance also suggests setting the hot water tank thermostat to 60°C to cut your bills¹⁸. Scotland's draft compliance guidance adds a requirement for solid fuel systems: a cylinder thermostat and a zone valve or three-port valve should be fitted to control the temperature of stored hot water³³.

Not every room thermostat touches hot water at all: a standard one controls heating only. Some smart thermostats can, though. Which?'s smart thermostat reviews note that the Google Nest Learning Thermostat (Gen 3) can control hot water, with professional installation recommended, and that the Hive Thermostat V4 can control hot water, with frost protection, GPS tracking, program modes and a child lock³⁴. Whether yours can depends on the model and on the system it is fitted to. The full picture of cylinder thermostats, timers and zoning for hot water is in our guide to hot water controls, and the day-to-day use of the programmer is covered in heating programmers and timers.