The cheapest winter is the one you sort out in autumn, while it is still mild enough to get up a ladder and early enough to book a boiler service before everyone else does. None of this is exciting and very little of it costs much, but a home that is sealed, insulated and set up sensibly holds the same warmth on noticeably less gas or electricity. Work down this list over a weekend or two before the cold really lands, and you go into winter paying less to feel exactly as warm.
If you do only three things. Turn your boiler's flow temperature down to around 55C to 60C, seal the obvious draughts around doors and windows, and set the heating timer to match when you are actually at home. All three are free or nearly free, and together they can take a real bite out of a winter heating bill without you ever feeling colder.
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Book the boiler service before the rush
Do this first, because it is the one job that depends on someone else's diary. An engineer who can come next week in September will be booked solid the moment the first cold snap hits and boilers start failing. A service keeps the boiler running efficiently and, more importantly, safely, and it is the moment to catch a small fault before it becomes a cold house in January. While you are at it, glance at the pressure gauge yourself: if it reads below about 1 bar when the heating is off, the system needs topping up, a two-minute job with the filling loop. And do not wait for the first frost to find out the heating works. Fire it up for ten minutes on a mild day, check every radiator warms and listen for anything odd, so any problem surfaces while it is still easy to fix.
Turn the flow temperature down
This is the biggest free saving most people have never touched. A combi boiler often leaves the factory set to send water to the radiators at 70C, 75C or even higher, which pushes it out of its efficient condensing mode and wastes gas. Turning the flow temperature down to around 55C to 60C lets the boiler condense properly and can trim gas use by something like 6 to 12 per cent in a typical home. The rooms still reach the same temperature; they just warm a little more gently, which on a home left heating for hours you will barely notice. It costs nothing and takes a minute once you know which control to change, and the boiler flow temperature guide shows you exactly which dial that is. Note this is the flow temperature on the boiler, not the room thermostat, which is a separate setting.
Hunt down the draughts
Sealing draughts is cheap, quick and one of the most cost-effective jobs in the house. The usual culprits are the gaps around external doors, the letterbox and keyhole, an unused chimney, gaps under skirting and between floorboards, the loft hatch, and old extractor or air vents that no longer do anything. A few pounds of self-adhesive strip, a brush seal for the door and a chimney balloon deal with most of it, and the full run-through is in the draught-proofing guide. One warning: do not block ventilation that is there on purpose. Air bricks, trickle vents in window frames and the extractor fans in the kitchen and bathroom are there to carry moisture out, and sealing them up trades a small draught for damp and mould, which is a far worse and more expensive problem.
Check the loft before it is too cold to bother
Heat rises, so an uninsulated or thinly insulated loft is where a lot of your gas quite literally goes through the roof. The recommended depth is around 270mm, and a surprising number of lofts have half that, or a layer that has been squashed flat by years of boxes stored on top. Topping it up is one of the best-value jobs going, and September is a far more pleasant time to do it than a freezing January, as covered in the loft insulation guide. While you are up there, lag any water pipes and the cold water tank, because an uninsulated pipe in a now better-insulated loft is colder than before and more likely to freeze. The cheapest heat is the heat you never lose in the first place.
Set the controls for your real routine
Every hour the heating runs is an hour of warmth you are paying to replace as it leaks away, so the single best habit is to heat the house only when someone is in it. Set the timer to your actual routine, coming on before you wake and switching off after you have left or gone to bed, rather than ticking over all day out of habit. On the thermostat, somewhere between 18C and 21C suits most homes, and each degree you turn it down saves roughly 5 to 10 per cent of your heating cost, so it is worth finding the lowest setting that still feels comfortable in a jumper. The thermostat savings calculator puts a pound figure on what a single degree is worth in your home. If your radiators have thermostatic valves, turn them down in the rooms nobody uses so you are not paying to heat a spare bedroom to the same warmth as the lounge.
Bleed and balance the radiators
A radiator that is cold across the top while warm at the bottom has air trapped inside, and bleeding it with the little key takes seconds and gets the whole panel working again. Do this before winter and the boiler heats the rooms faster and runs less. If a radiator is cold at the bottom instead, that points to sludge settling inside, which a plumber can clear, and if the far radiators never seem to get as hot as the near ones, the system needs balancing so the flow is shared out evenly. These are small jobs, but a set of radiators all pulling their weight means the house reaches temperature sooner and the boiler switches off sooner, which is money saved on every heating cycle.
The cheap jobs that quietly pay for themselves
A scattering of small, low-cost fixes add up. Thick curtains drawn at dusk keep heat in through the glass, as long as they hang in front of the window and not over the radiator. A sheet of reflective panel behind a radiator on an external wall bounces heat back into the room. A draught excluder at the bottom of a door, a cover over an unused fireplace, and simply pulling the sofa off the radiator so it is not soaking up the warmth all help. For the times you are sitting still of an evening, heating the person rather than the whole house is far cheaper, so an electric blanket or a heated throw at a few pence an hour beats turning the central heating up, a trade-off explored in portable heaters running cost. To price any of these habits in your own money, the appliance running cost calculator does the sums.
Guard against the deep freeze
A proper cold snap brings its own risks, and a little preparation avoids an expensive mess. Lag any exposed pipes, especially in the loft, the garage and against outside walls, and make sure you know where the main stopcock is so you can shut the water off fast if a pipe does burst. If you go away over winter, leave the heating on a low frost setting rather than off entirely, so the pipes never get cold enough to freeze. The other winter problem is condensation and the mould that follows it, which comes from warm damp air meeting cold glass and walls. Run the extractor fan when cooking and showering, wipe the worst off the windows in the morning, and try not to dry washing on radiators in an unventilated room, because all that moisture has to go somewhere.
The one-evening version
If autumn has got away from you and the cold is already here, there is a quick version that captures most of the benefit in an evening. Turn the boiler flow temperature down. Seal the front door and the letterbox. Draw the curtains at dusk. Set the heating timer to your real hours instead of all day. Drop the thermostat by a single degree and see if you notice. Those five take under an hour between them, cost next to nothing, and will have you paying less from the very next heating cycle, with the bigger jobs like the loft and the radiators to follow when you get the chance.
Common questions
What is the most important thing to do before winter?
Book the boiler service early and turn the flow temperature down to around 55C to 60C. The service depends on an engineer's diary that fills up fast once the cold hits, and the flow-temperature change is a free adjustment that can cut gas use by several per cent with no loss of comfort.
How can I cut my heating bill without spending money?
Turn the boiler flow temperature down, set the timer to heat only when you are home, drop the thermostat by a degree, bleed the radiators, and close the curtains at dusk. None of these cost anything, and together they can take a noticeable amount off a winter bill.
Should I leave the heating on low all winter?
Only when you are away, on a frost setting, to stop the pipes freezing. When you are home it is cheaper to heat the house to the temperature you want during the hours you are actually in, using the timer, than to leave it ticking over all day, because every hour of heating is heat you pay to replace as it escapes.
How do I stop condensation and mould in winter?
Let the moisture out rather than trapping it. Run the extractor fans when cooking and showering, keep trickle vents and air bricks clear, wipe condensation off cold windows, and avoid drying washing on radiators in a closed room. Do not seal up intentional ventilation when draught-proofing.