Start with the cheapest warmth you can buy

Before you consider a new boiler, underfloor heating or triple glazing, it is worth spending an afternoon hunting for draughts. Cold air sneaking in through a letterbox or a gap under a back door does two things at once: it chills the room, and it makes your heating work harder to compensate. Sealing those gaps is one of the few home improvements that costs pence and pays you back within the same heating season.

Most traditional UK homes have between five and ten obvious draught paths. You will not find them by standing in the middle of a room looking thoughtful — you will find them with the back of your hand, on a cold windy day, moving slowly around the edges of doors, windows and any hole in the wall. Here are the five jobs that make the biggest difference for the least money and fuss.

1. Letterboxes and keyholes

A metal letterbox flap on a UPVC door is essentially a hole in your front wall with a hinge on it. When the wind hits it, it lifts, and cold air pours straight into your hallway. A brush-style letterbox draught excluder is usually under £10, screws or clips over the existing flap, and can be fitted in ten minutes with a screwdriver. Choose one with a metal face and a nylon brush seal rather than a thin foam pad, which will flatten within a month.

• Fit an internal brush seal behind the external flap if you have room — two seals are far better than one.
• For keyholes, replace the standard escutcheon with a covered one that has a hinged flap and a foam backing pad, or simply fit a self-adhesive keyhole cover over the existing plate.
• Check the door itself is not warped. If the letterbox surround is split or loose, seal behind it with a little silicone before fitting the excluder.

2. Doors — internal and external

An external door typically leaks in three places: along the bottom, down the hinge side and around the frame where it meets the wall. The bottom is the worst offender. If you have a gap of more than about 5mm, a brush or rubber strip screwed to the inside face of the door is the cheapest fix; a slide-on draught excluder or a "draught snake" only works as a stopgap.

• Bottom of the door: a brush seal for carpet, a rubber blade seal for hard floors, or a hinged automatic seal that lifts as the door opens. Look for one that can be trimmed to length.
• Sides and top: self-adhesive foam or E-profile rubber strip in the rebate is fine for a snug frame. On older timber doors, a screw-fixed brush carrier lasts far longer than foam.
• Frame to wall: run a bead of decorator's caulk or frame sealant around the internal edge of the architrave. Gaps here are often hidden behind skirting and picture rails.
• Internal doors: worth doing too, especially between a cold hallway and a heated living room. Sealing them is what makes a "heat the room you are in" strategy actually work.

3. Chimneys and fireplaces

An open chimney is a large, well-designed hole for warm air to escape and cold air to fall into. In a home with an unused fireplace, this alone can account for a noticeable slice of your heat loss.

• Chimney balloon: an inflatable pillow that wedges inside the flue. Around £20–£30 and fitted in minutes. It still allows a small amount of ventilation, which reduces condensation risk.
• Chimney sheep: a recycled wool plug on a handle, similarly effective and easy to remove for the summer.
• If you never use the fireplace at all, a properly fitted solid flue plug or a capped chimney with a ventilated cowl is the best long-term answer.
• Important: never block a flue that serves an open fire, a gas fire, a wood burner or any gas appliance. Gas appliances need permanent ventilation, and a blocked flue can be lethal. If in doubt, leave it alone and speak to a registered gas engineer.

4. Windows, trickle vents and overlooked gaps

Sash windows are notorious: the gap between the two sliding frames and the gaps at the meeting rail. Purpose-made brush or wiper seals that screw into the staff bead are the neat solution, and they let the window still open. On casement windows, renew the foam or rubber gasket in the rebate if it has perished. Although it sounds minor, a sash window with four new seals feels dramatically less cold to sit next to.

Then check the things nobody thinks about: the gap around a loft hatch, the air brick you have covered with a plant pot, the pipe and cable entry points through the external wall (seal with mortar or exterior sealant, not expanding foam alone), and the extractor fan flap that no longer closes. Each is a small job. Together they can make a real difference.

5. Do it safely, and do not over-seal

Draught-proofing works best when it is targeted rather than total. Homes need some fresh air to control moisture, and a house sealed too tightly will grow condensation on windows, black mould in corners and stale, stuffy air. Leave trickle vents open if you have them, keep bathroom and kitchen extract fans working, and never seal an air brick that feeds a gas boiler, fire or stove.

Bathrooms and kitchens need more ventilation, not less, so draught-proof the doors but keep the extract running. If you live in a listed building or a conservation area, check before making changes to external doors, windows or chimneys — reversible measures such as internal brush seals and chimney balloons are usually the safest route. Get the five jobs above done before the cold snap arrives, and your boiler will thank you for it.