Sealing Draughts: The Cheapest Energy Work in Any House
2 min read · Last reviewed February 2026
Air leakage is invisible, unglamorous, and usually the largest single heat loss you can fix in a weekend.
Insulation slows conduction through a surface. Air sealing stops warm air leaving through gaps. In an older house the second is frequently the bigger loss, and it costs a fraction as much to fix.
Find the leaks without a blower door
Pick a cold, windy day. Close all windows and external doors, turn on extractor fans to depressurise the house slightly, and walk the perimeter with a lit incense stick. Where the smoke pulls sideways, air is moving.
Where the leaks actually are
| Location | Typical share of leakage | Fix |
|---|---|---|
| Loft hatch and ceiling penetrations | High | Draught strip and a rigid insulated hatch |
| Floorboard and skirting gaps | High | Flexible filler or acrylic sealant |
| Letterbox, keyholes, cat flaps | Moderate | Brush seals |
| Window and door perimeters | Moderate | Compression seals, not foam tape |
| Service penetrations under sinks | Underrated | Expanding foam or grommets |
| Unused chimney | Very high when open | Removable chimney balloon |
Do not seal everything
Houses need ventilation. Keep trickle vents, extractor fans, and airbricks serving suspended floors or combustion appliances clear. The goal is to eliminate uncontrolled leakage while keeping controlled ventilation intact — sealing without ventilating causes condensation and mould.
Run the numbers for your own project
- Energy Savings CalculatorWill this upgrade pay for itself?
- Insulation R-Value CalculatorWhat R-value do I need, and how much?
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