How the Draft Proofing Calculator Works

Enter number of external doors, openable windows and chimneys in your home, plus extras like letterboxes and loft hatches. The calculator totals sealing materials required, prices the job both as DIY and professional installation and estimates yearly savings at current energy prices.

The honest headline figures from Energy Saving Trust, draught proofing windows and doors saves a typical semi detached home around £30 to £45 a year, with an open chimney adding roughly £20 to £50 more. The bigger win is indirect, a draught free home feels warmer at same temperature and turning thermostat down a single degree saves around £90 a year on top.

Where Homes Actually Leak

Draughts concentrate in predictable places and finding them takes minutes. On a windy day run a hand around window frames, external doors and skirting boards, watch for moving curtains and listen for whistling. Visible daylight under a door is a guaranteed leak. The usual suspects:

• Gaps between openable windows and their frames
• External doors: edges, the bottom gap, the letterbox and even keyhole
• Open chimneys in unused fireplaces
• Loft hatches, which behave like an uninsulated door to coldest space in the house
• Gaps around pipework passing through walls
• Floorboard and skirting gaps in suspended timber floors

An open chimney deserves special mention because it works like a window left permanently ajar, drawing heated air up and out all day.

Materials and What They Cost

The materials are cheap and choice is mostly about lifespan. Self adhesive foam strip costs least and fits in minutes but compresses and fails within a couple of years. Rubber, brush or wiper strips in metal or plastic carriers cost a little more and last many times longer, which makes them better buy for doors and frequently opened windows. Doors take a brush strip at the bottom, a letterbox brush at around £10 to £15 and a keyhole cover. Chimneys take a removable chimney balloon or draught excluder at £40 to £100 or a terracotta cap from around £150 fitted at the pot. Gaps around pipes fill with silicone sealant and larger voids with expanding foam.

A whole house done DIY typically costs £50 to £180 in materials. Professional draught proofing runs £200 to £600 for a three bed semi, earning its premium on sash windows and warped period doors where routed in brush seals outperform anything stick-on. Either way payback arrives within two to five years, faster than almost any other efficiency measure.

The Ventilation Line You Must Not Cross

Draught proofing seals uncontrolled leaks, not deliberate ventilation and distinction protects both your health and building. Never block trickle vents in window frames, airbricks serving suspended floors or wall vents in rooms with open flue or flueless gas appliances, which need fixed ventilation to burn safely. Internal doors should keep their gap at bottom so air circulates, kitchens and bathrooms still need their extractor fans doing exactly what draught proofing prevents elsewhere.

Homes without any planned ventilation can already be too airtight, in which case sealing further invites condensation and mould. The rule of thumb, seal the gaps you never chose, keep the vents somebody designed in.

Worked Example

A three bed semi with 8 openable windows, 2 external doors, 1 unused chimney and a loft hatch:

• Window sealing: around 40m of brush or rubber strip
• Doors: 2 perimeter strip sets, 2 bottom brushes, a letterbox brush and keyhole cover
• Chimney: one removable draught excluder
• Loft hatch: strip around the frame, matching a door treatment
• DIY cost: roughly £100 to £150 in decent materials
• Expected saving: £50 to £95 a year directly, more with the thermostat nudged down

At those numbers the materials pay for themselves by the second winter.