Short answer: EPA estimates that air sealing and adding insulation in attics, crawl spaces and basements saves homeowners an average of 15% on heating and cooling costs, or about 11% of total energy costs (ENERGY STAR). Start in the attic: it’s usually the easiest place to work and the biggest leak.
Why it beats new equipment
A new furnace or heat pump makes heat more efficiently, but a leaky house lets it escape just as fast. Sealing and insulating shrink the amount of heat you need in the first place, which helps whatever system you have now and lets you buy a smaller one later. The DOE estimates that reducing drafts alone can save 10-20% a year on energy (energy.gov).
Step 1: Find the leaks
- Attic: gaps around plumbing vents, wiring holes, recessed lights, the chimney and the attic hatch.
- Basement and crawl space: where the house framing sits on the foundation (the rim joist), and around pipes and dryer vents.
- Living areas: baseboards, outlets on outside walls, window and door frames.
On a windy day, hold a stick of incense or a damp hand near suspect spots. A professional blower-door test finds the rest; many utilities offer low- or no-cost assessments. See how to do a home energy audit yourself.
Step 2: Seal first, then insulate
| Gap type | Best material |
|---|---|
| Small cracks (under 1/4 inch) at trim, frames | Caulk |
| Larger gaps around pipes and wires | Expanding spray foam |
| Doors and operable windows | Weatherstripping and door sweeps |
| Outlets and switches on exterior walls | Foam gaskets behind the cover plates |
| Around chimneys and flues | Metal flashing and high-temperature sealant (never foam) |
Insulation slows heat moving through materials, but air still flows through it. That’s why sealing comes first: insulation laid over open gaps works far less well.
Step 3: Add insulation where it counts
- Attic floor: if you can see the tops of the ceiling joists, you probably need more. Blown-in cellulose or fiberglass is the usual choice.
- Basement and crawl space: the DOE suggests at least R-25 for these areas, and R-19 or more at the foundation perimeter.
- Ducts in unheated spaces: seal joints with duct mastic and insulate to at least R-6, per the DOE.
DIY or hire a pro?
- DIY-friendly: caulking, weatherstripping, outlet gaskets, attic hatch insulation.
- Usually worth a pro: blown-in attic insulation in tight attics, crawl space encapsulation, anything involving knob-and-tube wiring, asbestos or vermiculite (which may contain asbestos), and spray foam in large areas.
Safety: don’t seal what needs air
The DOE warns that tightening a house can cause fuel-burning appliances (furnaces, water heaters, fireplaces) to backdraft. Have combustion appliances checked after major sealing work, and make sure you have working carbon monoxide alarms. Keep attic soffit vents clear when adding insulation.
What it’s worth
With heating and cooling at about $900 a year for an average household (ENERGY STAR), a 15% saving is about $135 a year, and it keeps paying every year with no maintenance. It also makes rooms more comfortable and less drafty. For more quick wins, see 12 ways to cut your winter bill.
FAQ
Can a house be too tight? Very tight homes need mechanical ventilation. Typical older homes are far from that point.
Are there rebates? Many utilities and some state programs pay for insulation and air sealing. See energy rebates still available.