How do I find out where my house is losing heat?

Heat leaves through the fabric — walls, roof, windows, floor — and through gaps as moving air. Both matter, but draughts are far cheaper to address and give the fastest return, so they are the sensible starting point.

What you'll need

• Your hand
• A candle or incense stick (optional)
• Torch (optional)

Step by step

1. Survey on a cold windy day with the heating on.Draughts are only detectable when there is a temperature and pressure difference. A mild still day tells you nothing.
2. Use a candle or incense stick to find draughts.Hold it near edges and watch the smoke or flame move. It reveals gaps you cannot feel, particularly around frames and floors.
3. Check the loft hatch and loft insulation.Roughly 270mm of insulation is the modern standard. Older houses often have far less, and the hatch itself is usually a bare uninsulated panel.
4. Check around windows and doors.The frame edges, the opening seals, letterboxes and keyholes. These are the cheapest and quickest fixes with the fastest payback.
5. Check the floor.Gaps between boards and at the skirting, and any unblocked hatch or underfloor void. Suspended timber floors can lose a substantial amount.
6. Check unused chimneys.An open unused chimney is a continuous hole to the outside. A chimney balloon or sheep's wool draught excluder is inexpensive and immediately effective.
7. Feel the walls in different rooms.A noticeably cold external wall suggests missing cavity insulation or a solid wall. That is a bigger job, but it identifies where the largest losses are.
8. Prioritise by cost and payback.Draught-proofing first, then loft insulation, then cylinder and pipe lagging, then windows and walls. That is roughly the order of return on money spent.

Tips

• A thermal imaging camera or a thermal attachment for a phone makes this dramatically easier and they can often be borrowed from a library or community energy group.
• Do not seal a house completely. Ventilation is needed to prevent condensation and damp — draught-proof deliberate gaps, not air bricks and vents.
• Many areas have free or subsidised home energy assessments. They identify the largest losses and any grants you qualify for.

Common mistakes

• Sealing every vent and air brick — They are there deliberately. Blocking them causes condensation, damp and in some cases dangerous flue problems.
• Starting with expensive measures — Draught-proofing and loft insulation have far shorter paybacks than windows or wall insulation. Do the cheap things first.
• Surveying on a mild still day — Draughts need a temperature and pressure difference to be detectable. A cold windy day reveals what a mild one hides entirely.

Questions people ask