A drafty window quietly drains your wallet all winter. Cold air slips through the gaps, your furnace runs longer to keep up, and your energy bill climbs. Sealing those leaks can trim 10% to 20% off your heating and cooling costs.
There is more at stake than money. The same gaps let in moisture, and standing dampness around a window feeds mold that is bad for the house and the people in it.
Below you will find how to seal a window on both sides, which sealant to grab for each job, and a handful of cheaper tricks for renters and quick seasonal fixes.
Key Takeaways
- Seal the stationary joints around the frame with caulk, and seal the moving sash with weatherstripping.
- Use paintable latex caulk indoors and flexible silicone outdoors, where it shrugs off rain, UV, and temperature swings.
- Find hidden drafts by running your exhaust fans to depressurize the room, then passing a lit incense stick around the window edges.
- For wide frame-to-wall gaps use low-expansion spray foam; add shrink film, storm windows, or thermal curtains for cheap seasonal heat savings.
Sealing Windows: Inside vs. Outside
You need to tackle both sides, but the material changes depending on where you stand. Silicone around the exterior frame creates a waterproof barrier against rain and wind. Inside, caulk closes the gaps where the trim meets the wall to stop air infiltration and tidy up the look.
There is a simple rule for what goes where: caulk seals the stationary joints that never move, while weatherstripping seals the moving parts like the sash. Get that split right and the job pays for itself fast, air sealing this way usually returns its cost in a year or less.
Some draft-stopping methods, like shrink film or adhesive weatherstripping, are strictly interior jobs.
Caulk vs. Silicone: Which Is Best?
While you can technically use either, they serve different purposes. Caulk is the go-to for interior gaps because it dries faster, creates a hard shell, and is paintable. It cleans up easily with just soap and water.
Silicone is the heavy hitter for exterior window frames. It withstands extreme heat, freezing cold, and heavy rain without cracking. It stays flexible after curing, meaning it moves with your house as it expands and contracts.
However, silicone is a bit trickier to work with. It takes longer to dry, smells stronger, and requires solvents (like mineral spirits) to clean up.
Cheat Sheet: Caulk vs. Silicone
Here is a quick breakdown to help you grab the right tube at the hardware store.
Caulk
Pros
- Dries quickly.
- Paintable surface.
- Easy to smooth and remove.
- Water cleanup.
- Perfect for trim and baseboards.
Cons
- Prone to cracking outdoors.
- Usually lacks fungicides.
- Can shrink over time.
Silicone
Pros
- Flexible and durable.
- Water, UV, and temperature resistant.
- Often contains mold inhibitors.
- Best for glass, metal, and vinyl.
Cons
- Cannot be painted.
- Messy cleanup requiring chemicals.
How to Find Window Leaks
Before you buy a single tube of caulk, pinpoint exactly where the air is sneaking in. The classic trick is to light an incense stick or a candle and hold it near the window joints on a windy day. If the smoke flickers or blows sideways, you have found a leak.
Here is how to make those leaks obvious: depressurize the room first. On a cool, windy day, close the windows, turn off your furnace, and switch on every exhaust fan that vents outside, your clothes dryer, bathroom fans, and the kitchen range hood. That pulls household air out and drags outdoor air in through every gap, so the incense smoke reacts much harder right at a real leak.
For a no-tools version, use the “palm test.” Wet your hand slightly and run it along the edges of the frame on a cold day. You will feel the temperature drop where the draft hits.
If you love gadgets, a temperature sensor like this Google Nest can help monitor room temps to identify which rooms are losing heat fastest. Sketch a quick floor plan and mark every drafty spot as you go.
Check the obvious places first: where the sashes meet, around the window locks, and where the frame meets the drywall.
Step-by-Step: Sealing Your Windows
Checking your seals should be a standard part of your fall maintenance routine. Ignoring it just costs you money. Let’s get your home airtight.
Tools You Will Need
- Paintable latex caulk (for inside).
- Outdoor silicone sealant (for outside).
- Caulk gun.
- Mineral spirits (for silicone cleanup).
- Soapy water and a rag.
- Utility knife.
- Putty knife or 5-in-1 tool.
- Expanding spray foam (window and door formula).
Sealing Exterior Frames
When working outside, your main goal is water management. You are looking at the gap where the window frame meets the siding or brick.
Sometimes the gap between the window and the wall is wider than expected. For deep pockets, expanding spray foam is your best friend, but buy the low-expansion type made for windows so it doesn’t bow the frame.
- Clean the area. Use a stiff brush or rag to remove dirt, debris, and peeling paint. Sealant won’t stick to dirt.
- Remove old sealant. If there is old, cracking silicone, cut it out with your utility knife or scrape it away. Wipe the surface down with mineral spirits to ensure a clean bond.
- Fill deep gaps. If you find large voids behind the trim, carefully apply spray foam. Fill it about 50% full, as it expands. Let it cure (usually a few hours), then trim the excess flush with a knife.
- Apply silicone. Load your gun and run a smooth bead of silicone where the frame meets the exterior wall.
- Tool the bead. Use a wet finger or a caulk tool to smooth the bead, ensuring it seals both sides of the gap.
Sealing Interior Windows
Interior sealing is about comfort. You want to stop that cold breeze from hitting your neck while you watch TV.
- Prep the surface. Clean the frame with soapy water to remove dust and grease. Let it dry completely.
- Scrape old caulk. Use your putty knife to remove any loose or ugly old caulk.
- Apply the caulk. Cut the tip of the tube at a 45-degree angle. Load the gun and apply a steady bead along the seam where the window trim meets the wall.
- Smooth it out. Run a wet finger along the bead to press it into the gap and create a smooth, professional look. Wipe excess off your finger with a wet rag.
- Paint. Wait for the manufacturer’s recommended drying time before touching it up with paint.
Pro Tip
Other Ways to Stop the Drafts
Sometimes caulking isn’t enough, or maybe you are renting and can’t make permanent changes. Here are other effective ways to keep the cold out.
Install Storm Windows
Storm windows act as a second layer of defense. They create a dead air space that insulates your home, significantly reducing heat loss. They come as exterior attachments or interior inserts. Note that they work best on double-hung windows and can be tricky to use with casement windows that crank outward.
Apply Window Insulation Film
Shrink film is essentially “shrink wrap” for your windows. It is cheap, effective, and strangely satisfying to install.
Clean your frames with rubbing alcohol (or mineral spirits) and let them dry. Apply the double-sided tape included in the kit around the perimeter of the frame. Press the plastic film onto the tape, leaving a few inches of overhang.
Once it is up, grab a hair dryer. Set it to high heat and blow it over the film. The wrinkles vanish as the plastic shrinks tight, creating a clear, airtight barrier.
Refresh the Weatherstripping
Weatherstripping seals the moving parts of your window, the parts caulk can’t touch because they slide. Over time, foam tape disintegrates and rubber seals flatten out, so plan to replace it every few years.
The material you pick decides how long the fix lasts. Felt and open-cell foam are cheap, but they wear out fast and don’t block air especially well, so save them for low-use windows. Vinyl costs a little more, resists moisture, and holds up. Metal strips like bronze or aluminum are affordable and last for years.
Self-Adhesive Foam Tape
This is the easiest DIY fix. Buy a roll of high-density foam tape, clean the bottom of the sash where it hits the sill, and stick the tape on. When you lock the window, the foam compresses to block the air.
V-Strip (Tension Seal)
For a longer-lasting seal, use V-strip inside the tracks of sliding or double-hung windows. It springs open against the sash to block drafts without making the window hard to close. Cut each strip to the length of the sash plus about an inch on each end so it covers the full travel.
Use Draft Stoppers
For a low-tech solution, place a draft snake (a fabric tube filled with sand or beans) along the window sill. It physically blocks air from entering at the bottom of the window. You can buy them or make your own from old socks and rice.
Hang Thermal Curtains
Curtains don’t seal the window itself, but they trap cold air between the glass and the fabric, keeping it from cooling your room. Look for “thermal” or “blackout” curtains with a heavy lining. For the best result, they should reach all the way to the floor or seal against the sill.
FAQs
Does Caulking Windows Save Energy?
Yes. Sealing the air leaks around your windows can cut 10% to 20% off your yearly heating and cooling costs, according to the Department of Energy (1). Caulk closes the fixed gaps where the frame meets the wall, so your furnace and AC stop fighting outdoor air, and the payback is usually a year or less.
Can You Temporarily Seal a Window?
Yes. Shrink film is the most popular temporary fix, and it peels off in spring with no residue. Removable weatherstrip caulk (sometimes sold as “peelable” or rope caulk) is another option that strips away in a single string when warm weather returns.
How Much Does It Cost to Seal a Window?
DIY sealing is cheap. A tube of quality silicone or caulk runs $5 to $10, weatherstripping rolls cost $5 to $15, and a shrink-film insulation kit is usually $10 to $20. Professional window replacement, by contrast, costs thousands, which makes sealing the highest-return first move.
When Is the Best Time to Seal Windows?
Seal during dry weather when the temperature sits between 40°F and 80°F (4°C to 27°C). If it is too cold, the caulk won’t cure properly; if it is raining, the sealant won’t bond to the exterior surface. Early fall, before the first hard freeze, is ideal.
Should You Caulk a Window Shut?
No. Only caulk the stationary joints, like where the trim meets the wall or where the glass meets the frame. Caulk is meant for fixed gaps, while weatherstripping handles the parts that move, so seal the operable sash with weatherstripping instead or you will glue the window closed.
How Do Professionals Find Air Leaks?
They run a blower door test. A technician mounts a powerful fan in an exterior doorway, depressurizes the whole house, and measures exactly how much air is leaking, often using a smoke pencil to pinpoint each gap. It is worth booking if drafts persist after you have sealed the obvious spots.
Seal the Deal
Sealing your windows is one of the cheapest home upgrades with a real payback, and most of it is a weekend job. Whether you run a full bead of exterior silicone or just tape up shrink film for the season, the sooner you close the gaps the sooner your furnace gets a break.
Left alone, small leaks turn into rot and mold, and those are the repairs you actually pay for. Grab a caulk gun, seal the gaps, and settle into a warmer room and a smaller energy bill this winter.
