You know the spot. The chair by the window where you can feel the cold on the back of your neck, or the bedroom that is always five degrees colder than the rest of the house. Old fixes like a rolled towel on the sill still help. But a few cheap materials and an afternoon will do a lot more.
Step 1: Find the leaks
The Department of Energy suggests an easy test. On a windy day, hold a lit incense stick near the edges of windows and doors. If the smoke wavers or blows sideways, you have found a leak. Keep it away from curtains and blinds, and don't do it near a fireplace or a gas appliance that is running.
Check these spots on every window:
- Where the window frame meets the wall
- Where the sashes meet each other in the middle
- Along the bottom of the sash and the sill
- Around the window lock
Mark each leak with a piece of painter's tape so you can find it again.
Step 2: Use the right fix for the spot
The DOE's rule of thumb is simple:
- Caulk seals cracks between things that don't move, like the gap between a window frame and the wall.
- Weatherstripping seals around things that do move, like a window sash or a door.
Caulking a window frame. Scrape out old cracked caulk, wipe the joint clean and dry, and run a steady bead along the gap. Smooth it with a wet finger or a caulk tool. Pick a caulk labeled for windows and for indoor or outdoor use, depending on the side you are sealing.
Weatherstripping a window. Self-stick foam tape works for many windows where the sash closes against the frame. V-strip (a folded strip of vinyl or metal) fits along the sides of double-hung sashes. Clean the surface first, and make sure the window still closes and locks.
Step 3: Plastic film for the worst windows
For a drafty old window you won't replace this year, an interior window insulation kit is hard to beat. ENERGY STAR describes the method: stick double-sided tape around the window trim, press on the clear plastic film, then use a hair dryer to shrink it tight and smooth. ENERGY STAR says the film can reduce drafts, air leaks, condensation, and heat loss.
A few tips:
- Clean the trim first so the tape sticks.
- Leave the film a little loose before you heat it, then work the hair dryer from the corners in.
- Peel the tape slowly in spring so it doesn't pull off paint.
Step 4: Curtains and shades
The DOE recommends opening curtains and shades on south-facing windows on sunny winter days to let the sun warm the room, and closing them at night to hold the heat in. Insulating cellular shades or heavy lined curtains help most on drafty windows.
Step 5: Don't forget the doors
A door sweep on the bottom of an exterior door, or a draft stopper laid along it, blocks a common leak. The DOE lists both.
Make a draft snake: sew a fabric tube about 3 inches across and a few inches longer than the door is wide. Fill it with dry rice or clean play sand, and sew the end shut. An old pair of jeans legs or a long sock works in a pinch.
Is it worth it?
ENERGY STAR says the EPA estimates homeowners can save an average of 15 percent on heating and cooling costs by air sealing and adding insulation. That number is for the whole house, sealing and insulation together, not for one window. Still, sealing the windows you can feel is one of the cheapest places to start.
A word about old paint
If your house was built before 1978, the EPA says to assume the paint contains lead unless a test shows otherwise. Scraping, sanding, or prying on old window trim and sashes can make dangerous lead dust. Follow the EPA's lead-safe work practices (linked below), keep kids and pets out of the room, and hire a lead-safe certified contractor for bigger window work.
Grandpa nailed up storm windows in the fall and Grandma rolled a towel against the door. Today's caulk, weatherstripping, and plastic film do the same job with less work. Start with the window you can feel from your chair.