What is a door with a letterbox draught excluder?
A letterbox draught excluder is a fitted cover or brush seal that blocks airflow through the letterbox slot while still allowing mail delivery. It is a low-cost, DIY-friendly upgrade that can save a typical home between £5 and £15 per year on heating bills, according to the Energy Saving Trust (Energy Saving Trust, 2026). The product fits over or inside the letterbox opening on a front door, using bristles, flaps, or a magnetic cover to stop draughts.
Standard letterbox slots can let in cold air, rain, dust, and noise because the internal flap alone often does not seal tightly. A draught excluder reduces uncontrolled airflow without preventing the postman from pushing letters through. Typical models include external brush strips, internal magnetic covers, or combined brush-and-flap units.
Quick numbers cost, energy saving, and payback for a letterbox draught excluder
| Product type | Typical retail cost (£) | Annual heating bill saving (£) | Payback period (years) | DIY installation difficulty |
|---|---|---|---|---|
| Brush strip excluder | £5–£15 | £5–£10 | 0.5–3.0 | Easy |
| Magnetic cover excluder | £8–£20 | £7–£12 | 0.7–2.9 | Easy |
| Combined brush-and-flap unit | £12–£30 | £10–£15 | 0.8–3.0 | Moderate |
These figures are based on the Energy Saving Trust draught-proofing cost calculator and DESNZ household energy efficiency data (Energy Saving Trust, 2026; DESNZ, 2026). Actual savings depend on house size, fuel type, and the severity of the existing draught. Installation time ranges from 5 minutes for a clip-on brush strip to 30 minutes for a screw-fixed combined unit.
How much heat a letterbox draught excluder can save per year
Draught-proofing a letterbox can save a typical semi-detached home between £5 and £15 per year on heating bills, depending on house size and fuel type. The saving comes from reducing the volume of cold air entering and warm air escaping through the slot. Combined with other draught-proofing measures (doors, windows, chimneys), total annual savings can reach £50–£60 per household (Energy Saving Trust, 2026).
The exact saving varies with three main factors: the size of the gap around the letterbox flap, the wind exposure of the front door, and the heating system type (gas central heating vs. electric storage heaters). Ofgem typical domestic consumption values show that a gas-heated semi-detached home uses around 12,000 kWh per year for heating (Ofgem TDCVs, 2026). A letterbox draught is a small but persistent leak that a £10 excluder can eliminate for years.
The different types of letterbox draught excluder and how they work
Brush strip excluders are fitted to the inside or outside of the door, with nylon or rubber bristles that part when mail is pushed through. They are the most common type and cost £5–£15. Magnetic cover excluders use a flap with a magnet that seals against a metal plate on the door, opening only when mail is inserted. These are slightly more expensive at £8–£20 but provide a tighter seal against rain and wind.
Combined brush-and-flap units integrate both a brush seal and a hinged flap for double protection against draughts and rain. Some models include a built-in letter cage to catch mail and reduce noise from the slot. Product specifications from UK building materials suppliers show that combined units typically last 5–10 years before the brush bristles or hinge need replacement (MCS product certification database, 2026).
How to check if your letterbox already has an effective draught excluder
Test by holding a piece of tissue paper or a candle flame near the letterbox slot on a windy day. If it moves, air is leaking through. Inspect the existing flap: if it is warped, cracked, or does not sit flush against the door frame, it is not sealing properly. Check for gaps around the letterbox plate itself, where it meets the door surface, these are common leak points (Energy Saving Trust DIY draught-proofing checklist, 2026).
Use a smoke pencil or thermal leak detector for a more accurate assessment. TrustMark guidance recommends checking all external openings, including letterboxes, as part of a whole-home draught-proofing survey (TrustMark, 2026). Many modern uPVC doors come with a brush strip integrated into the letterbox, but these can wear out after 5–7 years and need replacement.
MCS certification and installer verification for letterbox draught excluders
Letterbox draught excluders are typically DIY-installed, but if you hire a handyperson or draught-proofing specialist, check they hold TrustMark accreditation. MCS certification is not required for letterbox excluders, it applies to renewable energy systems such as heat pumps and solar panels (GOV.UK, 2026).
For broader door draught-proofing work (e.g., replacing a complete door or fitting a new letterbox), use a FENSA-registered installer if the work involves a replacement door under Building Regulations. Always ask for a written quote and a description of the product being fitted before any work begins. TrustMark scheme rules require all registered tradespeople to provide clear documentation and a complaints process (TrustMark, 2026).
How to choose the right letterbox draught excluder for your door type
Measure the internal width and height of the letterbox slot, most standard slots are 230–250 mm wide and 35–50 mm high. For uPVC doors, choose a model that clips onto the existing letterbox plate without drilling; for wooden doors, screw-fixed brush strips are common. For composite doors, check the manufacturer’s warranty before fitting any adhesive or screw-fixed excluder, some warranties restrict modifications (FENSA guidance on door modifications, 2026).
Consider whether you need a rain-deflecting model if the door faces prevailing wind or rain. Magnetic cover excluders with a weather seal are best for exposed locations. If you have a letter cage or a non-standard letterbox size, check product dimensions carefully, some combined units only fit slots up to 250 mm wide. The MCS product certification database lists approved models for different door types (MCS, 2026).
