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The short answer: to stop drafts from windows, seal the gaps by type — use caulk on the fixed joints around the frame and where it meets the wall, and weatherstripping on the moving sash edges that open and close. For single-pane and older windows, add a shrink-film insulation kit for the winter, and block the base with a draft snake. Start with the cheapest fixes; the US Department of Energy notes that sealing air leaks is one of the most cost-effective ways to lower heating and cooling bills.
We do not renovate homes first-hand; this guidance follows Department of Energy weatherization recommendations and the consensus of home-efficiency sources, as described in how we rank. Window drafts waste real money every heating season, and most of them are fixable in an afternoon for a few dollars.
First, find the window drafts
Before sealing anything, locate exactly where air is getting in, because sealing the wrong spot wastes effort. On a windy or cold day, try one of these tests along every window edge:
- Candle or incense test. Hold a lit candle or a stick of incense near the edges and watch the flame flicker or the smoke stream sideways where air leaks. This is the most sensitive quick test.
- Hand test. Slightly dampen the back of your hand and move it slowly around the frame; moving air feels cool on wet skin.
- Tissue or ribbon test. Hold a thin tissue near the gaps and watch for movement.
Check the usual suspects: the sash edges that move, the meeting rail where an upper and lower sash overlap, the joint where the frame meets the wall, and the base of the window. Mark each leak so you know what you are treating.
Caulk the fixed window gaps
Caulk seals the parts of a window that do not move — the joints around the frame and the gap where the frame meets the wall, inside and out. It is cheap, and it addresses the leaks people often overlook because they are not near the moving sash. Clean and dry the joint first, remove any old cracked caulk, then run a smooth bead into the gap and tool it with a wet finger or a caulking tool so it fills the space and seals cleanly. Use an exterior-grade caulk outdoors.
The one rule: never caulk the moving parts of the window, or you will glue it shut. Caulk is for the fixed joints only; the moving edges get weatherstripping instead.
Weatherstrip the moving parts
Weatherstripping seals the sash edges that slide or swing when you open the window, and it comes in several forms suited to different gaps:
| Type | Best for | Notes |
|---|---|---|
| Adhesive foam tape | Flat surfaces, the base of a sash | Cheapest and easiest; compresses to seal |
| V-strip (tension seal) | Sliding sash channels | Springs open to seal a moving edge; durable |
| Rubber or vinyl gasket | Where a sash presses closed | Long-lasting, good seal on a closing edge |
| Rope caulk | Temporary winter seal | Peels off in spring; good for windows you will not open |
Measure the gap, choose a strip thick enough to fill it when the window closes, clean the surface so adhesive sticks, and apply it so the window still opens and latches. Replace weatherstripping that has hardened or flattened, since worn strips no longer seal.
Add a window insulation film kit
For single-pane and older windows, a shrink-film insulation kit is one of the best inexpensive winter fixes, which is why the Department of Energy lists it among low-cost weatherization measures. It creates a sealed pocket of still air over the whole window — an insulating layer that cuts both drafts and heat loss through the glass itself, not just around the edges. You apply double-sided tape around the frame, stretch the clear plastic film over it, then shrink it tight and wrinkle-free with a hair dryer until it is nearly invisible.
The film peels off cleanly in spring. It is especially worthwhile on windows you do not need to open during winter. Our step-by-step is in how to install a window insulation kit.
Block the base and cover the drafty glass
Two more low-cost layers help. A draft snake — a fabric tube laid along the bottom of the sash or the sill — blocks the draft that slips in at the base, and you can buy one or make one from a rolled towel. Over the glass, insulating window coverings add a barrier: cellular (honeycomb) shades trap air in their pockets and are the most effective, and thermal or heavy curtains reduce both cold-window drafts in winter and heat gain in summer.
These do not seal the leak the way caulk does, but they slow the movement of cold air off the glass into the room, which is a big part of what a draft feels like. For the curtain option, see best thermal curtains in our furniture and window-covering coverage.
Fixes by window type
The right combination depends on what kind of window you have, because the leak paths differ:
| Window type | Where it leaks | Best fix |
|---|---|---|
| Double-hung (slides up and down) | Sash edges, the meeting rail, the base | V-strip in the channels, foam at the base, seal the meeting rail |
| Casement (cranks open) | The gasket around the closing sash | Replace the compression gasket; adjust the latch to pull it tight |
| Sliding (moves sideways) | The sliding edge and the track | Brush weatherstrip on the sliding sash; clean the track |
| Single-pane (any style) | The glass itself plus the edges | Add a film kit over the whole window for the winter |
| Old or historic | Loose sash, worn putty, gaps everywhere | Rope caulk and an interior storm or film kit; avoid gluing it shut |
Single-pane and older windows lose the most and benefit most from the film kit, because they leak through the glass and not only around the edges. For windows you never open in winter, rope caulk plus film is a cheap, reversible way to seal them tight until spring.
Seal the rest of the house too
Windows are rarely the only leak. Doors, ducts, attic hatches, and gaps around wall penetrations all let conditioned air escape, and sealing them together delivers the real savings the Department of Energy points to. Weatherstrip exterior doors the same way you do windows — see how to weatherstrip a door — and check the ductwork, covered in how to seal leaky air ducts. Attic insulation is the biggest single win in many homes: how to insulate an attic.
When to replace a drafty window instead of sealing
Sealing beats replacing for draft control in almost every case, at a tiny fraction of the cost and with a fast payback. Reserve full window replacement for windows that are genuinely failing: rotted frames, broken sashes, or double panes that have fogged because the seal failed, and for whole-home renovations where new windows are already on the plan. For draft control alone, replacement is a major expense with a long payback, so work through the low-cost fixes first.
Stopping drafts is one half of a warmer, cheaper home; the other is making the most of the heat you have — see how to make a room warmer. The rest of our efficiency and comfort guidance is at the heating and cooling hub, and how we make recommendations is explained in how we rank.