Most advice about energy-efficient heating jumps straight to replacing your boiler. But for most homes, the cheapest savings come from getting more out of the system you already have: lower flow temperatures, controls that are set up properly, a system that’s been looked after, and less heat leaking out of the house.
This guide covers those changes, roughly in order of cost, starting with the free ones. If you’re already sure your system needs replacing, our complete guide to upgrading your home heating is the better place to start. If you’re not sure, our guide to the signs your heating system needs upgrading will help you decide.
The short version
- Free first: set the thermostat to the lowest comfortable temperature, tighten your heating times, and keep radiators clear.
- Combi boiler? Turn the radiator flow temperature down to 60°C or below. It’s one of the biggest no-cost changes you can make.
- Controls matter more than gadgets: a room thermostat, a programmer and working TRVs set room by room do most of the work.
- Look after the system: bleed radiators, clean the magnetic filter, and have it serviced every year.
- Then stop the heat escaping: loft insulation and draught-proofing are the cheapest building upgrades.
Start with the free changes
- Find your lowest comfortable temperature. For most people, that’s somewhere around 18°C to 20°C. Each degree lower can cut heating use by up to around 10%, so it’s worth trying a degree down for a week to see if you notice.
- Match the heating times to your day. Most boilers only need to come on 30 to 60 minutes before you need the warmth and can go off half an hour before you go to bed or leave the house.
- Turn down, not off, when you’re away for a night or two. It avoids damp and condensation, and reheating a cold house from scratch takes a lot of energy.
- Keep radiators clear. Sofas and long curtains in front of a radiator trap the heat. Close curtains at dusk, but tuck them behind or above the radiator.
- Use free heat. Open curtains on sunny winter days, and keep internal doors shut between warm and cold rooms.
Turn down your boiler’s flow temperature
The flow temperature is how hot the boiler heats the water going round your radiators. Many boilers are left at the factory setting of 70°C to 80°C. A condensing boiler only works at its best when the water coming back to it is cool enough to condense the flue gases, which a high flow temperature prevents.
If you have a combi boiler, Nesta’s Money Saving Boiler Challenge recommends a radiator flow temperature of 60°C or below. It doesn’t affect the hot water from your taps and shower, and it’s easy to change back. Rooms take a little longer to warm up, so you may need to bring the heating on slightly earlier. Most boilers have a separate dial or menu setting for the radiator temperature; check your manual or the Nesta site for your model.
If you have a hot water cylinder, it’s less straightforward, because the cylinder needs to reach 60°C to keep it safe from legionella bacteria. Some systems can heat the cylinder and the radiators at different temperatures; others can’t. Ask your heating engineer at the next service whether yours can be set up that way.
Lower flow temperatures are also good practice if you’re thinking about a heat pump. If your home stays comfortable with the boiler at 50°C to 55°C, that’s a good sign your radiators can cope with the lower temperatures a heat pump runs at.
Get the controls right
Good controls aren’t about having the latest app. They’re about the boiler only running when, and where, heat is needed. A well-controlled system usually has:
- A programmer or timer for heating and, if you have a cylinder, hot water.
- A room thermostat in a main living area, away from radiators, sunlight, and draughts.
- Thermostatic radiator valves (TRVs) on most radiators, set lower in bedrooms and rooms you use less. Leave the radiator in the room with the main thermostat without a TRV, or fully open, so the two don’t fight each other.
- Weather or load compensation, where the boiler supports it. These adjust the flow temperature automatically to suit the weather or how far the room is from its target, so the boiler runs gently for longer instead of blasting on and off.
Smart thermostats and smart TRVs add room-by-room scheduling and remote control. They’re useful if your routine varies or some rooms sit empty for long periods, but they only save money if you use them to heat less. Our guide to smart thermostats and controls compares the main options, and our guide to TRVs covers whether yours are worth upgrading.
Keep the system in good order
- Bleed the radiators at the start of each winter, or whenever one is cold at the top. It takes ten minutes with a radiator key. On a combi or sealed system, check the boiler pressure afterwards and top it up if it has dropped.
- Clean the magnetic filter, if you have one, once a year. Sludge from rusting pipes and radiators reduces flow and makes everything work harder.
- Have the boiler serviced every year by a Gas Safe registered engineer. A badly set-up boiler can waste fuel for years without anyone noticing.
- Ask about balancing. If the radiators near the boiler roast while the far ones stay lukewarm, the system needs balancing so each radiator gets its fair share of flow.
Cold patches at the bottom of radiators usually point to sludge, which may need a professional system clean. Our guide to central heating radiators covers this in more detail.
Stop the heat escaping
However efficient your heating, heat that leaks out of the house is wasted. The cheapest improvements usually give the quickest return:
- Draft-proofing around doors, windows, letterboxes, loft hatches, and unused chimneys. Much of it is DIY, and an old towel along the bottom of a door still works.
- Loft insulation, topped up to at least 270 mm.
- Cavity wall insulation, if your walls have an unfilled cavity.
- Thermal curtains or secondary glazing where replacing windows isn’t an option.
Our home insulation guide compares the costs and savings, and our guide to insulation grants covers what funding is available.
Check you’re on the right tariff
If you heat with gas, a fixed tariff mainly protects you from price rises rather than cutting your use. If you heat with electricity, whether through a heat pump, storage heater, or electric radiator, a time-of-use tariff can make a real difference, especially if you can shift heating or hot water into cheaper hours. Our guide to the best electricity tariffs for heat pump owners explains how they work.
If you have a heat pump
Heat pumps work best when they run steadily at a low temperature, holding the house at a constant warmth rather than heating it up and letting it cool. The on-off habits that suit a gas boiler, such as turning the heating off during the day and blasting it on in the evening, usually make a heat pump less efficient. Leave the weather compensation to do its job, avoid big setbacks overnight, and let the installer’s settings settle in before changing them. Our guide to how air source heat pumps work explains why.
When it’s time to upgrade instead
All of the above will make any system cheaper to run, but there comes a point where the boiler itself is the problem: frequent breakdowns, an old non-condensing model, or a system that can’t keep the house warm. At that point, the main options are:
- A new condensing boiler. There’s no ban on fitting a replacement gas boiler in an existing home; the government dropped the planned 2035 phase-out. See our guide to new boiler costs.
- A heat pump, with up to £7,500 off through the Boiler Upgrade Scheme.
- A hybrid system that pairs a heat pump with a boiler. The heat pump does most of the work, and the boiler takes over in the coldest weather. But please be aware that the boiler upgrade grant will not be available for this.
Hydrogen boilers aren’t something to plan around. The planned village trials at Whitby and Redcar were cancelled, and the government has said it will decide in 2026 whether hydrogen has any role in home heating. For a side-by-side look at the realistic options, see Compare Heat Pumps and Boilers.
Frequently asked questions
What is the most energy-efficient way to use central heating?
Set the thermostat to the lowest comfortable temperature, match the heating times to when you’re in, use TRVs to keep unused rooms cooler, and, on a combi boiler, turn the radiator flow temperature down to 60°C or below.
Is it cheaper to leave the heating on low all day?
For a gas boiler, usually not. Heating only when you need it generally uses less gas, although turning it down rather than off when you’re away for a day or two avoids damp. Heat pumps are different: they’re designed to run steadily, and big temperature setbacks usually cost more.
Will lowering the flow temperature affect my hot water?
On a combi boiler, no. The radiator and hot water temperatures are set separately. If you have a cylinder, it needs to reach 60°C for safety, so ask an engineer before changing anything.
How often should I bleed my radiators?
Once a year at the start of winter, and whenever a radiator is cold at the top but warm at the bottom.
Do smart thermostats save money?
They can, if you use them to heat fewer rooms for less time. On their own, they don’t reduce your bill; it’s the schedule and temperatures you set that do.
Are gas boilers being banned?
Not in existing homes. You can still replace a gas boiler with a new one. New homes built under the Future Homes Standard, which applies from 24 March 2027, will effectively need low-carbon heating instead.
Sources: flow temperature guidance from Nesta’s Money Saving Boiler Challenge; hydrogen trial status from The Chemical Engineer; boiler policy from Solar Power Portal.