Tip
Finding & sealing air leaks
Air leaks bypass insulation. A well-sealed home loses 30-50% less energy through the building envelope than a leaky one. Most homes have many small leaks adding up to a coffee-table-sized hole.
Where leaks happen (top to bottom)
- Attic — top plates of interior walls, plumbing/electrical penetrations, recessed lights, attic hatch, bathroom fans, chimneys
- Walls — outlet and switch boxes (especially exterior walls), windows and doors (perimeter caulking), where wall meets floor and ceiling
- Basement — rim joist (the band of wood at the top of basement walls), sill plate, plumbing penetrations through foundation, dryer vent, basement windows
- Floor — between unconditioned basement and floor above; between unconditioned crawlspace and floor
How to find leaks
- Smoke pencil or incense — light incense; walk slowly along walls and ceiling junctions; smoke movement = leak
- Hand-felt drafts — works at outlets and around windows on cold/windy days
- Blower door test — professional contractor pressurizes/depressurizes the house and uses thermal imaging to find leaks. ~$200-$400. Often offered free by utilities as part of "energy audit"
- Thermal camera (IR) — DIY rentals available; show temperature differentials
Materials by leak type
- Small gaps (≤ 1/4 inch): caulk (silicone for windows; latex for paintable surfaces)
- Medium gaps (1/4-1 inch): backer rod + caulk; or low-expansion canned foam
- Large gaps (> 1 inch): rigid foam board cut to fit + canned foam to seal edges
- Penetrations (pipes, wires): fire-rated foam or fire caulk if penetrating between floors
- Around outlets/switches: foam gaskets behind cover plates ($1-$2 each, simplest fix)