If your hallway is the coldest spot in the house on a January morning, the front door is almost certainly to blame. A typical 1930s UK front door — and plenty of 1990s replacements — leaks air around the threshold, through the letterbox, around the latch and through a hinge side that has dropped over the years. The fix takes one Saturday morning, costs under fifty pounds and stops a remarkable amount of cold air from invading the lower floor. Here is the full walk-through, including the parts that most online guides skip.
Why the Front Door Is the Biggest Single Air Leak
A standard timber front door has a perimeter of roughly five metres. A continuous one-millimetre gap around that perimeter is equivalent to a 50 cm by 1 cm slot — about the same as a window left permanently cracked open. Add a letterbox flap that no longer springs back, a worn brush strip along the bottom and a keyhole with no internal cover, and you have a draught that the central heating fights all winter.
Most domestic energy assessments (the EPC visit you get when selling) flag the front door as a significant heat loss point, but rarely with a specific fix. The good news is that every weak spot has a cheap, tested solution.
Diagnosing the Leaks Before You Buy Anything
On a still evening, close the door, switch off any extractor fans and slowly run a stick of incense or a lit candle around the entire frame, the letterbox, the keyhole and the threshold. Wherever the smoke or flame dances sideways, that is a leak. Mark each spot with a strip of masking tape.
Typical findings in a UK house:
- Threshold gap of 4 to 8 mm at the bottom — the biggest single leak.
- Top corner of the latch side, where the door has dropped over the years.
- Letterbox flap that no longer closes flush, especially on cold mornings.
- Keyhole with no internal escutcheon, blowing air straight into the hall.
- Hinge side, where one or more hinges has loosened.
The Threshold: Where Most of the Cold Air Enters
A worn brush strip on the bottom of the door is the most common cause. Replacement strips come in two main forms: a screw-on aluminium carrier with replaceable brush insert (best for solid timber doors) and a self-adhesive vinyl strip (acceptable for renters but less durable).
For a solid wood door, unscrew the old strip, clean the bottom of the door with a damp cloth, hold the new strip in place and pilot-drill before screwing — straight into hardwood without a pilot hole splits the bottom rail every time. The brush should just kiss the threshold without dragging when the door swings.
If the threshold itself is worn or non-existent, a stick-down rubber threshold seal (about twelve pounds at Screwfix or Toolstation) goes onto the floor under the door. Combined with a brush strip on the door, the two seals together close the gap completely.
The Letterbox: A Forgotten Heat Hole
A standard letterbox flap is just a hinged plate held closed by gravity. After a few years the hinge stiffens, the brush behind it flattens and the whole assembly stops sealing. Two upgrades work:
- Internal letterbox brush kit: a rectangular plastic frame with stiff bristles that mounts on the inside face of the door. Around eight to twelve pounds, takes ten minutes to fit. Postman can still push letters through; cold air cannot.
- Replacement letterbox with a heavy spring flap: sealed with an EPDM gasket all round. Costs fifteen to twenty-five pounds and looks tidier than an add-on brush.
Whichever route you choose, do not just rely on the external flap — almost every UK external letterbox leaks air after five winters.
The Frame: Compression Seals That Actually Stay Put
The gap between the door edge and the frame is sealed by a compression strip — usually self-adhesive EPDM rubber or P-profile foam. Cheap foam from a pound shop lasts one winter; quality EPDM (around twelve to eighteen pounds for a 10-metre roll) lasts a decade.
Clean the rebate of the frame with isopropyl alcohol, let it dry completely, then press the strip into place starting from one corner. The trick is to lay the strip into the rebate rather than onto the face of the frame — this way the door compresses it rather than scraping it off when it closes.
What to Do If the Door Has Dropped
An older timber door often sags on the latch side, leaving a wedge-shaped gap that no seal can fill. Before applying any strip, lift the door off its hinges, tighten the hinge screws (or replace short screws with 65 mm screws that bite into the studwork behind the frame). If the wood around the hinges has crumbled, drill out the holes, glue in matchsticks or wooden dowels and reposition the screws.
The Keyhole: The One Everyone Forgets
An internal escutcheon plate with a sprung cover costs about four pounds. It sits over the keyhole on the inside face of the door and snaps shut when the key is removed. On a windy night, you can feel the difference within seconds — the cold draught coming straight through the lock barrel is real, and worse on side-blown rain.
Common Mistakes to Avoid
- Using cheap foam tape on the frame. It compresses permanently after a few weeks and stops sealing.
- Fitting a brush strip too low. If the brush drags hard on the floor, the door jams and the strip wears out in a month.
- Skipping the letterbox. A gap the size of an envelope is a gap, full stop.
- Ignoring loose hinges. No seal compensates for a door that no longer sits square in its frame.
What It Costs and What You Get Back
Total bill for a thorough job: roughly thirty-five to fifty pounds in materials, plus one morning of work. Expected saving: between forty and seventy-five pounds a year on a gas-heated three-bed semi, depending on tariff. Just as important, the hallway stops feeling like an unheated room — and the front of the house no longer accumulates that thin film of street dust that always lands where cold air leaks inward.
Of all the small DIY jobs that quietly pay back year after year, a properly sealed front door is near the top of the list. The materials are at every builders' merchant, the techniques are simple, and the result is a noticeable upgrade in comfort the very next cold evening.