Why air sealing beats insulation
A 1 sq inch hole through your envelope leaks the same air at the same temperature delta no matter how much insulation surrounds it. Air leaks bypass insulation entirely — sealing them gives a bigger return per dollar than almost any other home improvement.
The materials kit (under $80)
- Caulk gun + 4 tubes of paintable acrylic-latex caulk ($15)
- 1-2 cans of expanding foam (yellow, gaps under 1") ($15)
- 1 can fire-rated foam (red, around flues/electrical) ($10)
- Backer rod for wide gaps ($5)
- Foam outlet gaskets, 12-pack ($5)
- V-strip weatherstripping ($10)
- Door sweeps, 2 ($20)
Where to seal, in order
- Attic floor penetrations: top plates, can lights, plumbing chases, attic hatch perimeter. Biggest impact because of the stack effect.
- Rim joists in the basement: the band where the foundation meets the floor framing.
- Exterior door perimeter and bottom: weatherstrip + sweep.
- Window sash channels and frame perimeter: V-strip + caulk.
- Outlet/switch gaskets on exterior walls.
- Wall penetrations: dryer vent, cable entry, exterior faucets, AC line set.
- Bulkhead door perimeter.
Safety
- Wear a respirator in the attic — old insulation contains particulate.
- Use fire-rated foam (red can) anywhere within 3" of metal flues, B-vents, or chimneys.
- Never seal combustion air intakes for furnaces, water heaters, or wood stoves.
- Backdrafting warning: if you have gas, oil, propane, or wood-burning appliances, a tighter house can pull exhaust (including carbon monoxide) back indoors or starve them of combustion air. Have a pro do a combustion safety test before and after air sealing, and keep working CO alarms on every level. See our Disclaimer.
- If your home becomes very tight, add an ERV/HRV for fresh air.
Verify with a blower door
Get a baseline ACH50 reading before sealing if possible (many utilities offer free audits), then re-test after. Most DIYers cut ACH50 by 30-50% with a single weekend of work. Plug the numbers into the ACH50 calculator to see your category.
Try the calculator
Draft & Air Leak Cost Calculator
Estimate yearly cost of overall air leakage and DIY savings.
DIY safety & liability notice
This guide is for general information only. Any work you do on your home is at your own risk. Energy Savings Toolkit is not responsible for improper installation, property damage, or injury. Follow product instructions and local codes, and hire a licensed professional for electrical, gas, HVAC, roofing, or structural work. See our Disclaimer.