Turning the thermostat down by one degree is one of the most widely repeated pieces of heating advice in the UK, and unlike many heating myths it is broadly accurate. But the amount it saves, and whether it is the right adjustment to make, depends on how well the house holds heat, how the heating system is controlled, and what is actually causing the home to feel cold in the first place. Understanding the mechanism behind the saving, and the circumstances where it works best and least well, allows you to make adjustments that genuinely reduce costs rather than simply reduce comfort.
If rooms feel cold at current thermostat settings and the temptation is to turn the thermostat up rather than down, the house cold diagnostic is worth working through first to establish whether the problem is the thermostat setting, heat retention, or a heating system issue that adjusting the dial will not fix.
Why reducing thermostat temperature by one degree saves fuel
A central heating system maintains room temperature by running heating cycles whenever the air temperature at the thermostat drops below the target setting. The lower the target, the less frequently and for shorter duration the boiler needs to run to maintain it. At a lower target temperature, the temperature difference between the interior and the exterior is also slightly smaller, which reduces the rate at which heat escapes through walls, windows, and other parts of the building envelope. Both effects compound: the boiler runs less, and when it does run, the house loses heat slightly more slowly because the indoor-outdoor temperature differential is smaller.
The frequently cited figure is that reducing the thermostat by one degree saves around ten percent on heating costs, though this figure varies significantly depending on the property, the existing thermostat setting, and outdoor conditions. In a well-insulated home where the boiler runs efficiently and the temperature differential is the primary driver of heat loss, the saving is closer to this figure. In a draughty or poorly insulated home where air infiltration and conductive heat loss dominate regardless of the thermostat setting, the saving from one degree is smaller because the boiler has to replace lost heat frequently at any target temperature. If you want to put a figure on what your current setup is likely costing, the WarmGuide heating cost calculator gives you a quick estimate based on your home and usage.
Turning the thermostat up does not heat the house faster
One of the most persistent and costly misunderstandings about room thermostats is that setting them higher makes the house heat up faster. It does not. A room thermostat is an on-off switch, not a throttle. When the room temperature is below the target, the boiler runs at its normal output. When the room temperature reaches the target, the boiler stops. Setting the thermostat to 25 degrees does not cause the boiler to produce more heat than setting it to 20 degrees: it simply keeps the boiler running for longer because the target is harder to reach.
The practical consequence of this misunderstanding is significant. Homeowners who turn the thermostat up sharply when the house feels cold, expecting faster warming, instead run the boiler for a longer cycle and often overshoot the comfortable temperature before the house settles. The house then feels too warm, the thermostat is turned down, and the cycle repeats. Fuel is consumed without any improvement in comfort. Setting the thermostat to the desired comfortable temperature and leaving it there allows the system to reach and maintain that temperature in the most fuel-efficient way available.
Does leaving heating on low all day cost less than using a timer?
The question of whether to leave heating running continuously at a lower temperature or to heat on a timer, allowing the house to cool between cycles, is one of the most debated pieces of heating advice in the UK. The honest answer is that it depends on the thermal characteristics of the specific building.
In a well-insulated home, the house loses heat slowly when the heating is off. The energy required to reheat from a cool temperature after the heating has been off for several hours is relatively small, because the fabric of the building has not cooled dramatically. In this case, heating on a timer uses less fuel than running continuously at a lower temperature, because the periods when the heating is off involve almost no fuel consumption, and the reheat cost is modest.
In a poorly insulated or draughty home, the house loses heat quickly when the heating is off. The temperature drops significantly within an hour or two of the boiler stopping, and the reheat cost from a cold building is high because the thermal mass of the walls, floors, and ceilings has cooled and needs to be warmed again before the air temperature reaches a comfortable level. In this case, the continuous low-temperature approach may cost a similar amount or less because it avoids the high-energy reheating peak, while maintaining a marginally more consistent comfort level. However, the correct long-term solution for a poorly insulated home is to improve the insulation, not to run the heating continuously. Continuous low heating in a draughty home simply heats the outside at a lower rate, which is cheaper than heating it at a higher rate but is not as effective as reducing how quickly heat escapes in the first place.
For most UK homes with reasonable insulation, a well-programmed timer that heats the house before occupied periods and allows it to cool during unoccupied hours uses less fuel than continuous low-level heating. The key is ensuring the programmed schedule matches actual occupancy rather than running heating during periods when the house is empty.
Heating on low costs more when the house has high heat loss
Running heating continuously at a low thermostat setting in a home with significant heat loss through uninsulated walls, draughty floors, or poorly sealed windows keeps the heating on for extended periods without building up meaningful warmth in the building fabric. The fuel is being consumed to replace heat that is escaping continuously, rather than to raise and hold the temperature of a well-retained building. In these conditions, heating on low costs more than the fuel bills of a well-insulated home on a timer, and the comfort level is still poor because the heat loss rate is high at any thermostat setting.
The appropriate response in these homes is to address the heat loss routes rather than to experiment with thermostat strategies. Loft insulation, draught sealing, and where practical wall insulation reduce the rate at which heat escapes and make any thermostat strategy more effective. Grant funding may be available to cover insulation costs for eligible households through the Warm Homes Local Grant. How each of these measures connects to fuel costs is covered in the complete guide to keeping a UK home warm for cheap. If draughts are the primary driver of heat loss, the most effective fixes are covered in the best draught stoppers for UK homes. If the house loses heat quickly after the heating turns off regardless of thermostat setting, why your house cools down so fast after the heating turns off covers the building fabric causes.
Smart thermostats and weather compensation
Smart thermostats that use occupancy detection, weather forecasting, or learning algorithms to adjust heating schedules automatically can reduce fuel consumption beyond what a standard programmable thermostat achieves, because they avoid heating empty homes and adjust the heating start time based on how cold it is outside. Weather compensation controls, which reduce the boiler flow temperature automatically when outdoor temperatures are mild, are particularly effective on condensing boilers where lower flow temperatures allow the boiler to operate in condensing mode and extract additional heat from flue gases.
The potential saving from a smart thermostat is typically more modest than the saving from improving building fabric, but it requires no physical work on the building and can be implemented quickly. In a home that is already well insulated and draught-proofed, smart thermostat controls represent one of the remaining meaningful improvements available without structural work. Whether smart thermostats are worth the investment for older homes is addressed in whether smart thermostats are worth it in older homes.
The relationship between thermostat setting and room comfort
Room comfort is not determined solely by air temperature. A room with cold walls, cold floors, or significant air movement from draughts will feel uncomfortable at 20 degrees, while a well-insulated room with warm surface temperatures can feel comfortable at 18 degrees. This is why reducing the thermostat by one degree in a well-insulated home is barely noticeable in comfort terms, while the same reduction in a draughty or poorly insulated room may feel immediately uncomfortable.
Improving the thermal quality of the room, warming the wall surfaces through insulation and reducing cold air movement through draught sealing, allows the thermostat to be set lower without any reduction in perceived comfort. This is the mechanism by which building fabric improvements reduce heating bills: they do not just slow heat loss, they change the relationship between air temperature and comfort so that the same comfort level is achieved at a lower thermostat setting. If specific rooms feel cold even at current thermostat settings, why one room never warms up covers the room-level causes that a thermostat adjustment cannot address.
Where to go from here
Reducing the thermostat by one degree does save money in most homes, and the saving is real enough to be worth doing without any loss of comfort if the house is reasonably insulated. The larger opportunity, however, is in the building fabric rather than the thermostat dial. A home that retains heat well achieves comfortable temperatures at lower thermostat settings, heats up from cold more quickly, and maintains comfort for longer after the heating turns off. Thermostat strategy works best as the final layer of optimisation on a home that already performs well thermally, rather than as the primary tool for managing a home with significant heat loss.
Set the thermostat to the lowest temperature that feels genuinely comfortable, use a timer schedule that matches actual occupancy, and invest the energy saved in identifying and addressing the heat loss routes that are making the current thermostat setting necessary in the first place.