How to Seal Air Leaks: A DIY Weatherization Guide

Before buying anything, locate where air is actually moving. On a windy or cold day, run the back of a damp hand around window and door frames, electrical outlets on exterior walls, and where pipes or wires pass through the wall. You will feel the drafts.

For a stronger test, turn on your kitchen and bathroom exhaust fans to depressurize the house, then hold a lit incense stick near suspected spots; the smoke will pull toward any leak. Mark each leak with tape so you can work through them systematically.

The largest air losses are usually hidden: the rim joist in the basement, gaps around plumbing and wiring penetrations, and holes where cables enter the house. Fill these with a high-expansion polyurethane foam like Great Stuff Gaps & Cracks, which handles voids up to about 3 inches and adds insulating value.

Shake the can, wear gloves, and apply in thin passes; the foam keeps expanding after it leaves the can. Do not overfill. Let it cure, then trim any excess flush with a utility knife once it is firm.

The gap between a window or door frame and its rough opening is a major leak, but standard foam expands hard enough to bow the jamb and bind the sash. Use a low-expansion product made for this, such as Great Stuff Window & Door, applied in a thin bead into the gap.

If the rough opening gap is wider than about an inch, press in backer rod first, then foam over it. After curing, trim flush before reinstalling trim so the casing sits flat.

Windows and doors move, so their gaps need a compressible seal, not rigid foam. Apply a self-adhesive vinyl V-seal along double-hung window sashes and door jambs; the folded strip springs open to fill the gap while still letting the window or door operate.

Clean the surface with rubbing alcohol first so the adhesive bonds, cut the strip to length, and press it firmly into the channel. Replace any old, flattened weatherstripping rather than layering over it.

The gap under an exterior door is one of the biggest single drafts, and neither foam nor V-seal reaches it. Install a screw-on aluminum-and-vinyl door sweep like the Frost King premium sweep, cut to the door width with a hacksaw.

Mount it on the interior side of an in-swinging door, set the height so the vinyl blade just touches the threshold without dragging, and use the slotted holes to fine-tune for an uneven floor.

After sealing, repeat the incense or damp-hand test to confirm each leak is closed. You should feel and hear the difference immediately at drafty doors.

If you are on a budget, prioritize the biggest, most-used openings first: the rim joist, the main entry door, and the leakiest windows. These deliver most of the energy savings, and you can work through smaller leaks over time.