How to Seal Windows for Winter - Home Methods
updated 11 July 2026
Quick answer
First find the leak: move a lit candle along the frame or do the paper test - if a sheet of paper slides easily out of the closed window, the seal pressure is too weak. On uPVC windows, switch the hardware to winter mode with an Allen key, and replace worn EPDM gaskets with new ones. Do not seal the window airtight or cover the trickle vents, because moisture will build up inside your home.
Step by step
- 1
Find the leaky spots
Move your hand or a lit candle along the joint between the sash and the frame and watch the flame - flickering gives away a draft. Be careful with an open flame near curtains. Also do the paper test: close the window on a sheet of paper and try to pull it out. If it slides out without resistance, the seal pressure at that spot is too weak.
- 2
Set uPVC hardware to winter mode
Around the edge of the sash, find the eccentric locking cams that engage the strikers in the frame. Turn them so the stronger side presses against the gasket, which is the winter setting. Depending on the hardware, you turn them with an Allen key, usually 4 mm, or with pliers; if you are not sure, check the window's manual. Adjust a little at a time and test, because too much pressure wears the gaskets out faster.
- 3
Replace worn EPDM gaskets
Pull the old gasket out of the groove, clean the channel and press the new one in along its full length. Pick a profile that matches the shape of the groove, and choose EPDM rubber over cheaper TPE, because it lasts longer. Do not stretch the gasket, or gaps will open in the corners once it shrinks - cut it with a slight surplus.
- 4
Seal wooden windows with tape
In older wooden windows, the quickest fix is self-adhesive weatherstripping tape in an E, P or D profile stuck to the rebate. The surface has to be clean and dry, otherwise the tape peels off within days. It is a temporary home fix, but it usually lasts one winter.
- 5
Seal the joint between frame and wall
If the draft comes from under the windowsill or along the edge of the frame, seal the joint between the frame and the wall. Outside, use weatherproof silicone; inside, use acrylic sealant, which you can paint over. This is not the same as sealing the moving sash.
- 6
Leave a path for ventilation
Do not seal the window shut permanently and do not block the trickle vents. Your home needs air exchange, otherwise vapor condenses on the glass and mold appears. If the window has a micro-ventilation or night-vent setting, use those instead of cutting off the air supply.
Winter and summer mode - how pressure adjustment works
Newer uPVC windows have eccentric cams on the sash that engage metal strikers in the frame. By turning a cam, you change its position relative to the gasket: the thicker side facing inward means stronger pressure, the winter mode; facing outward means weaker pressure, the summer mode. The cam usually has a line or a dot showing its position.
Only switch to winter mode when you actually feel a draft, because constant strong pressure wears the gaskets out faster. After winter, go back to the summer setting. Not all windows have adjustable hardware - on simpler models the pressure cannot be changed, and replacing the gaskets is what remains.
Gaskets, tapes and silicone - what goes where
EPDM gaskets go in uPVC and newer wooden windows, pressed into the groove of the sash or frame. Self-adhesive tapes are the fix for old wooden windows without a groove - you stick them to the rebate, where the sash meets the frame. Silicone and acrylic serve a different purpose: they seal the fixed joint between the frame and the wall, not the moving sash.
With wooden windows, also check the glazing putty where the glass meets the frame. Cracked putty lets air and water through, so sometimes it needs patching and repainting. It is more work than tape, but it fixes the problem at the source.
Do not seal the window airtight
The biggest mistake is sealing a window so tightly that there is no air exchange at all. An airtight home without ventilation quickly collects moisture - vapor condenses on the glass and mold shows up around the reveals. So do not block trickle vents or ventilation grilles, even if that is where the cold is coming from.
The goal of sealing is to remove uncontrolled drafts, not to cut off the fresh air supply. If rooms feel stuffy or the glass fogs up, crack the window open to the micro-ventilation or night-vent position. A controlled air supply still loses less heat than a wide-open sash.
Frequently asked questions
›How do I seal uPVC windows?
On uPVC windows, start by adjusting the hardware pressure - switch the eccentric cams to winter mode with an Allen key or pliers. If that is not enough, replace the EPDM gaskets in the grooves of the sash and frame. Save the silicone for the joint between frame and wall, not the moving sash.
›How do I seal windows with home methods?
The cheapest home method is self-adhesive weatherstripping tape stuck to the rebate, plus the paper test to find the leaky spots. On uPVC windows you buy nothing, because switching the hardware to winter mode is enough. Wash and dry the surface before applying the tape.
›What is the best way to seal windows for winter?
It depends on the window type. uPVC takes pressure adjustment and EPDM gaskets, old wooden windows take weatherstripping tape and glazing putty, and the joint between frame and wall takes silicone or acrylic. A candle or the paper test will show you where the heat escapes.
›How do I check where a window is leaking?
Move a lit candle along the frame - a flickering flame reveals a draft, but watch out for curtains. You can also close the window on a sheet of paper: if it slides out without resistance, the pressure at that spot is too weak. A damp hand will also pick up the stream of cold air.
›Can I tape my windows shut completely for winter?
It is not worth it. Sealing them completely cuts off the air exchange, so vapor condenses on the glass and mold appears. Seal only the uncontrolled drafts and keep the trickle vents clear, along with the option of micro-ventilation.