--- title: "Draught excluders and window insulation film | Home Comfort Lab" description: "Cheap draught proofing that makes a real difference: door excluders, letterbox brushes and window film." url: https://homecomfortlab.co.uk/heating/draught-excluders-and-window-film/ --- # Draught excluders and window insulation film Cheap draught proofing that makes a real difference: door excluders, letterbox brushes and window film. By [Pete Harvey](https://homecomfortlab.co.uk/about/), editor. Updated 14 October 2026. This page links to Amazon. As an Amazon Associate I earn from qualifying purchases. [More about how this site is paid for](https://homecomfortlab.co.uk/affiliate-disclosure/). ![A hallway where door and letterbox brushes stop cold air, while a trickle vent and air brick still let fresh air in.](https://homecomfortlab.co.uk/images/scenes/draught-excluders-and-window-film.svg) > **The short answer** > > Seal the gaps you didn't mean to have: under and around outside doors, the letterbox, and the edges of windows that rattle or whistle. Window film helps most on single glazing. Leave the ventilation you are meant to have alone, including trickle vents, air bricks and extractor fans, or you swap a draught for condensation and mould. ## Find the draughts first On a windy day, run the back of a damp hand slowly around each outside door and window frame, the letterbox, the keyhole, loft hatch and any gaps where pipes come through the wall. You will feel cold air moving where there is a gap. Gaps between floorboards and under skirting boards in older homes can let in a lot of cold air too. Make a list by room. Start with the gaps where you felt the strongest flow of air. Sealing those first makes the most difference to how warm the room feels. ## What not to block A home needs a steady trickle of fresh air to carry away the moisture from cooking, washing and breathing. Good draught proofing seals the accidental gaps and leaves the home's planned ventilation working. The Energy Saving Trust lists these as things to leave clear: - **Trickle vents**, the slots at the top of many window frames. Leave them open all the time. - **Air bricks and underfloor grilles**, which keep wooden floors and joists dry. - **Wall vents**, which let small amounts of fresh air into a room. - **Extractor fans** in kitchens and bathrooms, which remove damp air where most of it is made. - **Vents for gas fires, boilers or other fuel-burning heaters**, which they need to burn safely. The Energy Saving Trust also advises against draught proofing internal doors, and says a chimney draught excluder should never block the chimney completely. > **Blocked vents cause condensation** > > If you cover trickle vents or stuff an air brick, moist air has nowhere to go. It settles on the coldest surfaces, usually windows and the corners of outside walls, and mould follows. If a room already gets [wet windows every morning](https://homecomfortlab.co.uk/damp/why-are-my-windows-wet-every-morning/), it already needs more ventilation. Never block a vent for a gas appliance; if you are unsure what a vent is for, ask a Gas Safe registered engineer. ## Our picks These are chosen by what each type of product does against the gaps above. We haven't tested them ourselves. ### For the gap under an outside door Everlasting Comfort Twin Under-Door Draught Excluder - **Type:** Door excluder - **Size:** Fits doors 76 to 91cm wide An under-door excluder closes the gap between the bottom of the door and the floor, a common source of cold air in a hallway. Measure the width of the door before you buy, and check it clears your doormat. [View on Amazon](https://homecomfortlab.co.uk/go/dx-door-a/) ### For the letterbox Stormguard PVC Brush Letterplate - **Type:** Letterbox brush - **Size:** 335 x 75mm, for openings up to 279 x 45mm Brushes on the inside of the letterbox stop the wind blowing straight through while still letting post in. Measure the opening first, so the brush covers it fully. [View on Amazon](https://homecomfortlab.co.uk/go/dx-letter-a/) [Manufacturer specs](https://www.stormguard.co.uk/stormguard-products/pvc-brush-letterplate-no-flap/) ### For the edges of doors and windows tesa Insulation Weatherstrip Foam M - **Type:** Seal strip - **Size:** 6m, for gaps of 1 to 5mm A self-adhesive strip fills the gap where an opening window or an outside door meets its frame. Foam strips are the cheapest and easiest to fit but wear out sooner; brush or rubber strips last longer. Foam doesn't suit sliding sash windows. [View on Amazon](https://homecomfortlab.co.uk/go/dx-strip-a/) [Manufacturer specs](https://www.tesa.com/en-gb/consumer/tesa-insulation-weatherstrip-foam-m.html) ### For single-glazed windows tesa Insulation Window Film (05432) - **Type:** Window film - **Size:** 4m x 1.5m A film kit sticks a clear sheet to the window frame with double-sided tape, and a hairdryer shrinks it tight. The trapped layer of air between the film and the glass works a little like secondary glazing for the winter. [View on Amazon](https://homecomfortlab.co.uk/go/dx-film-a/) [Manufacturer specs](https://www.tesa.com/en-gb/consumer/tesa-insulation-film.html) ## Window film without the condensation Film keeps the room side of the window warmer, which can mean less condensation on the glass you can see. It also seals the window shut until spring, so plan where the fresh air will come from. 1. Keep at least one window in the room free of film, or put the film on the fixed panes only, so you can still open a window to air the room. 2. If the window has trickle vents, stick the tape to the frame below them so the vents stay uncovered and open. 3. Clean and dry the glass and frame before you fit the film. Any moisture you seal in stays there. 4. Test the tape on a hidden part of the frame first. On painted wood it can lift the paint when you take it off. If you rent, check with your landlord. ## Where else the heat goes Draught proofing is one of the cheapest ways to make a room feel warmer, but cold air also gets in through an unused open chimney, a loft hatch with no seal, and gaps around pipes. Thick curtains help at night, as long as you open them in the day so the glass can dry and the curtains don't trap damp air against it. [Heating cost per hour](https://homecomfortlab.co.uk/tools/heating-cost-per-hour/): Compare what it costs per hour to heat a room with a fan heater, oil radiator or gas central heating. ## Sources - [Energy Saving Trust: draught proofing](https://www.energysavingtrust.org.uk/home-insulation/draught-proofing) Checked 14 October 2026. ## Read next - [Why are my windows wet every morning?](https://homecomfortlab.co.uk/damp/why-are-my-windows-wet-every-morning/) (How to) Morning condensation means warm, moist air is meeting cold glass. What causes it and how to stop it. - [Heating cost per hour: throw, heaters, gas, oil and heat pump compared](https://homecomfortlab.co.uk/tools/heating-cost-per-hour/) (Calculator) Compare the hourly cost of a heated throw, electric blanket, plug-in heaters, and gas, oil, heat pump and electric central heating. - [Heated airer running costs](https://homecomfortlab.co.uk/heating/heated-airer-running-costs/) (Running costs) What heated clothes airers cost per hour and per load at the current price cap, and how that compares with a tumble dryer. - [Electric blanket and heated throw running costs](https://homecomfortlab.co.uk/heating/electric-blanket-running-costs/) (Running costs) What electric blankets and heated throws cost per hour, per month and per winter at the current price cap. --- As an Amazon Associate I earn from qualifying purchases. Links to shops are marked, and earning from them never decides what we recommend. [How this site is paid for](https://homecomfortlab.co.uk/affiliate-disclosure/). Running costs use 26.32p per kWh for electricity and 7.97p per kWh for gas, the [Ofgem price cap, Direct Debit average for England, Scotland and Wales](https://ofgem.gov.uk/news/changes-energy-price-cap-between-1-october-and-31-december-2026) for 1 October to 31 December 2026.