Before You Touch the Thermostat: Seven Free Checks That Keep Heat — and Money — Indoors

Every November I do the same thing: nudge the thermostat up, then spend the rest of the month mildly irritated about it. Last year I tried something different. I walked round the house with a notepad, a radiator key and a roll of kitchen foil, looking for the places where heat quietly leaves.

None of it cost a penny. All of it took less time than an episode of something on iPlayer. And by the time the genuinely cold weeks landed, the thermostat was sitting a degree lower without anybody in the house complaining.

Here's the checklist, in roughly the order that pays back fastest.

1. Start at the boiler, not the radiator

This is the one almost everybody skips. Most combi boilers leave the factory with the heating flow temperature set somewhere around 75–80°C. A condensing boiler only does its clever condensing thing when the water coming back to it is cool enough — which means a lower flow temperature, generally somewhere in the 60s, can genuinely cut the gas you burn for the same amount of warmth.

Have a look at the front panel or the manual. If there's a heating flow setting, try dropping it in steps rather than one big leap. Rooms will heat more slowly, so you may need to bring the schedule forward by half an hour rather than turning the dial up. If you have a hot water cylinder, leave the cylinder thermostat at 60°C or above — that one isn't a saving worth making.

2. Bleed the radiators properly

Cold at the top, warm at the bottom means air. A radiator key lives in most kitchen drawers and costs about a pound if yours has vanished. Open the valve a quarter turn, let the hiss out, close it the moment water appears. Work through the house, and don't overtighten.

One thing worth knowing: if the water that comes out is black or gritty, you've got sludge, and no amount of bleeding will fix it. That's a system flush and it involves a heating engineer, so budget for it rather than pretending you didn't see it.

3. Foil behind the radiators on outside walls

Kitchen foil, shiny side facing the room, taped to a bit of cardboard and slipped behind the radiator. It bounces radiant heat back into the room instead of letting it soak into a cold external wall. It looks faintly ridiculous, it costs nothing if the foil is already in the drawer, and it works.

Only bother on external walls. Behind an internal wall, you're reflecting heat into another room that's already warm.

4. Follow your curtains for a day

Open them on a sunny south-facing window in the morning and you get free heat. Close them at dusk and you keep it. That's the easy half.

The half people get wrong is the tucking. Long curtains hanging over a radiator act like a chimney: heat rises, hits the fabric, and gets funnelled straight at the glass. Tuck them behind the radiator, or shorten the drop. Same logic applies to sofas parked in front of radiators and washing draped over them — both make the boiler work harder for a room that never quite warms up.

5. Hunt draughts with the back of your hand

A wet finger or the back of your hand is more sensitive to moving air than your face is. On a windy day, work round the obvious suspects: letterbox, keyhole, the gap under the front door, loft hatch, floorboards near external walls, and any extractor fan with a flap that no longer closes.

Fixes here can be genuinely free. A rolled-up towel at the base of the door. A cloth over the letterbox overnight. A folded blanket over the loft hatch. None of it is elegant, all of it is reversible, and you'll feel the difference in the hallway within a day.

6. Set the valves room by room

Thermostatic radiator valves are the cheapest zoning system you'll ever own, and most of us leave them on the same number all year. Bedrooms can sit lower than living rooms. Spare rooms can sit lower still, with the door shut. Hallways don't need to be tropical.

While you're there: shut internal doors. A house where every door is open is a house heating itself evenly and expensively, whether anyone's in the room or not.

7. Check the hot water cylinder's coat

Put your hand flat on the cylinder jacket. Warm to the touch means you're paying to heat the airing cupboard. Older cylinders often have a thin, tired jacket; a decent replacement is cheap and pays back over a winter or two.

Also look at the thermostat. Sixty degrees is the sensible number — hot enough to keep the tank safe, not so hot that you're paying to blend it back down at the tap. If your cylinder is well insulated, half an hour of heating before the morning showers is usually plenty.

Do the free ones first, then stop

There's an entire industry built around convincing you that a warm house requires a purchase — thermal cameras, smart TRVs, draught excluders with a brand name on them. Some of that kit is fine. But the seven checks above cost nothing, take an afternoon between them, and will tell you far more about where your money is going than a gadget will.

Do them this week, note down what you found, and then leave it alone until next autumn. The trick isn't a one-off blitz — it's that the walk round the house becomes a habit, like checking the tyre pressure or reading your meter. Our ancestors called it "closing the curtains". We can call it an audit if it makes it feel more official, but the saving is the same either way.