Internal letterbox draught excluders: which type actually works?
An internal letterbox draught excluder covers the letterbox from inside the house, so the cold air, wind noise and rattling stop at the door. There are four common types. Here is how each one works, what goes wrong with it, and how to choose one that fits your door.
The short answer: brushes and foam are cheap but leave gaps and wear down as post pushes through. A flap that closes against a seal on its own, such as a magnetic flap, stops the draught properly and keeps working. Whichever you choose, measure your letterbox and check for bolts behind it before you buy.
The four types of internal letterbox excluder
1. Brush excluders
Two rows of bristles in a plastic or metal frame, screwed over the letterbox. The post pushes between the bristles.
Good: cheap and quick to fit. Watch out for: air still passes between the bristles, and the bristles flatten and splay as post is pushed through every day.
2. Plain internal flaps
A hinged flap (sometimes called a letterbox tidy) that hangs inside the letterbox and falls shut by its own weight or a spring.
Good: tidy and self-closing. Watch out for: nothing holds the flap tight against the door, so it lets air past and rattles in the wind.
3. Foam and stick-on seals
Self-adhesive foam or rubber strips or pads around the letterbox opening.
Good: very cheap. Watch out for: foam compresses and the adhesive lets go, so they usually need replacing within a season or two.
4. Magnetic flap excluders
A steel flap that magnets pull shut against a seal as soon as the post has gone through. The Magflap MK3 is this type.
Good: closes tight every time, has no bristles to wear out, and stays quiet in the wind. Watch out for: it costs more than a brush, and you need to check it fits your letterbox (below).
Brush or magnetic is the choice most people end up weighing. We compare them side by side in brush vs magnetic letterbox draught excluders.
Before you buy: three things to check
- The size of your letterbox. Measure the hole in the door from the inside. For the Magflap MK3 Horizontal, the hole must fit inside the 340 × 100mm plate, with flat door all round it. Portrait (upright) letterboxes need a vertical excluder such as the Magflap MK3 Vertical (90 × 260mm plate).
- Bolts or nuts behind the letterbox. Many outside letterplates are held on by bolts that stick out on the inside. The standard Magflap clears 9mm. If yours stick out further, choose the additional gasket, which clears 18mm.
- Your door. Internal excluders suit wood, composite, metal and uPVC doors. On uPVC, fit on the inside.
Not sure? Print our free full-size fit template and hold it against your door, or email a photo of your letterbox to info@magman.uk and we'll tell you what you need.
Fitting an internal excluder
Most internal excluders screw straight to the inside of the door, centred over the letterbox. Take off any old brush or tidy first and wipe the surface clean. Hold the new excluder in place, mark the screw holes, and screw it on. The Magflap MK3 comes with all its fixings and takes about 10 minutes with a PZ2 screwdriver.
Magflap MK3 Horizontal
All-steel magnetic letterbox draught excluder, made in Leicester since 2009. Four finishes, an optional lock, and an extra gasket for bolts.
From £41.99 · Free UK delivery · Free 30-day returns · 1-year guarantee
See the Magflap MK3Upright letterbox? See the VerticalQuestions people ask
Will the post still come through?
Yes. Post pushes the flap open and it closes behind it. With a magnetic flap the magnets pull it shut again straight away.
Can I fit it on the outside instead?
The Magflap MK3 can be fitted inside or outside. Most people fit it inside, where it keeps the outside of the door unchanged. On uPVC doors, fit it inside.
My letterbox is big. Will it fit?
For the MK3 Horizontal, the hole needs to fit inside the 340 × 100mm plate with flat door around it. If you're unsure, use the printable template or send us a photo.
Can I stop someone fishing through the letterbox?
Yes. Add the locking keyset when you order (+£3), and you can lock the flap from inside, for example when you're away.
My keyhole is draughty too.
The Mini Magflap covers a mortice keyhole the same way. Add it with a Magflap and you get £3 off it automatically at checkout.