How do I stop heat escaping through doors and the letterbox?

Draughts are cold air arriving faster than the heating can warm it. Sealing the deliberate gaps is cheap and effective; the one crucial exception is any ventilation that a boiler, fire or stove depends on.

What you'll need

• Draught excluder strip
• Brush door strip
• Letterbox brush (optional)
• Keyhole cover (optional)
• Screwdriver

Step by step

1. Find the draughts on a windy day.Hold a lit candle or an incense stick near the edges of doors and windows and watch the smoke. It shows exactly where air is coming in.
2. Identify vents that must stay clear first.Air bricks, trickle vents and any vent serving a gas appliance, open fire or stove. These are not draughts — blocking them risks carbon monoxide. If unsure, leave it and ask a registered engineer.
3. Fit a brush strip to the bottom of external doors.The biggest single gap in most houses. Screw-on brush strips work better and last longer than stick-on ones.
4. Seal round the door frame.Self-adhesive foam or E-profile rubber strip in the rebate. Clean the surface first with sugar soap or it will peel off within weeks.
5. Fit a letterbox brush and a keyhole cover.A letterbox is a hole straight through the door. Both are inexpensive and take minutes.
6. Deal with internal doors to unheated rooms.Doors to a garage, an unheated utility or a cold hallway. A simple fabric excluder helps considerably.
7. Seal gaps around the frame itself.Where the frame meets the wall. Decorator's caulk for small gaps, expanding foam for larger ones, then made good.
8. Check the loft hatch.Often overlooked and effectively a hole into an unheated space. Draught strip around the edge and insulation on the back of the hatch.

Tips

• Do this before turning the heating up. It is far cheaper and it addresses the cause rather than compensating for it.
• A house needs some ventilation. Sealing every gap in a modern airtight house causes condensation and mould — trickle vents exist for a reason.
• Heavy curtains that reach the floor and a draught excluder at the front door make a room feel noticeably warmer for very little money.

Common mistakes

• Blocking air bricks or appliance vents — Fuel-burning appliances need air. Blocking their ventilation risks carbon monoxide poisoning, which is potentially fatal.
• Sealing a house completely — Moisture from cooking, washing and breathing has nowhere to go, and you trade draughts for condensation and mould.

Questions people ask