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The first cold month brings a bill that looks wrong. Usually the furnace is fine. The heat is leaving through gaps you can’t see: around doors and windows, through outlets on outside walls, past the attic hatch, along the top of the basement wall.
Energy Star estimates that sealing leaks and adding insulation saves the average home about 15% on heating and cooling. Most of the sealing part is an afternoon and about $40.
Find the leaks first
Pick a windy day. Close every window, shut the fireplace damper, and turn on the bathroom and kitchen exhaust fans. That pulls air in through every gap in the house.
Now walk the rooms with a lit incense stick. Hold it near window frames, door edges, outlet covers on outside walls, the attic hatch and any pipe that runs through a wall. Where the smoke bends sideways or flutters, air is moving. Mark each spot with painter’s tape.
No incense? A damp hand works. You’ll feel the cold line.
Where the air usually gets out
- Exterior doors. The gap under the door and along the latch side is often the single biggest leak in the house. If you can see daylight, you’ve found it.
- Windows. Not the glass, the frame. Old caulk shrinks and cracks.
- The attic hatch. A loose panel in the ceiling is a chimney for warm air.
- Outlets and switches on exterior walls.
- Where pipes and cables come through walls, floors and the rim joist in the basement.
Seal the big ones first
Doors: a door sweep across the bottom and foam weatherstrip along the frame. About $25 for a door, 30 minutes with a screwdriver and scissors.
Window frames, outside: exterior silicone caulk in the gaps between the frame and the siding. Any gap you can slide a credit card into is worth filling.
Window frames, inside: removable caulk or foam tape on windows you won’t open until spring.
Outlets: foam gaskets behind the cover plate, about $5 for a pack. Turn off the breaker first.
The attic hatch: a strip of foam weatherstrip around the frame, and a piece of rigid foam board glued to the top of the panel.
What not to bother with yet
New windows cost thousands and pay back over decades. A new furnace is a big decision for spring, not a fix for November. Start with the gaps: it’s the cheapest heat you’ll ever buy.
Our winterize your home checklist puts all of this in order, with the rest of the fall jobs.