Cold Draughts & Seals: Finding and Fixing Window Draughts

Cold draughts make a room feel chilly even when the heating is on. They also waste heat you’ve paid for, and they often get worse each winter as seals age.

The good news is that most draughts from windows and doors come from a handful of causes. Many of them cost little to fix.

Here’s how to find them, what causes them and how they’re fixed, plus the ventilation you should never block.

Why cold draughts matter

A draught isn’t just uncomfortable. It’s warm air leaving your home and cold air taking its place, so the heating works harder for the same comfort.

Draughts also create cold spots near windows and doors. As a result, people often turn the thermostat up to compensate, which costs more than fixing the gap.

The Energy Saving Trust describes draught-proofing as one of the cheapest and most effective ways to save energy at home. Windows and doors are usually the first places to look.

That said, not all airflow is bad. Trickle vents and extractor fans provide controlled ventilation, which keeps condensation and mould at bay. The aim is to stop uncontrolled draughts, not to seal the house shut.

How to find cold draughts

You don’t need any tools. Choose a windy day, ideally when the wind is blowing against the side of the house you’re testing.

1. Back-of-hand test: move the back of your hand slowly around each frame, sash, letterbox and keyhole. You’ll feel even a small draught.
2. Incense test: hold a lit incense stick near the edges. If the smoke flickers or blows sideways, air is getting through. Keep it well away from curtains and blinds.
3. Paper test: close a sheet of paper in the window at several points. It should grip firmly. If it slides out easily, the seal isn’t pressing tight.
4. Torch test: after dark, ask someone to shine a torch around a door from outside. Any light you see inside marks a gap.

Where to check first

• The opening edge of each sash, on the handle side.
• The top corners of external doors.
• Letterboxes, keyholes and cat flaps.
• The bottom of doors and the threshold seal.
• The joint between the frame and the wall, inside and out.
• Trickle vents, with the shutter closed.

Make a note of every draught you find. Often, one window or door turns out to be responsible for most of the problem.

The most common causes of cold draughts

Worn or shrunken gaskets

Rubber gaskets run around the sash and the frame. Over the years they flatten, harden and shrink, especially at the corners. As a result, gaps open up where the window should seal.

To check one, press it with a fingertip. A healthy gasket feels soft and springs back. If it’s hard, cracked, flattened or pulling away at the corners, it’s time for a new one.

Loose compression

Many uPVC windows have adjustable locking cams that control how tightly the sash presses against the seals. If they’re set loose, the window closes but doesn’t seal. A small adjustment often cures it.

A dropped sash or door

When a sash or door drops, it no longer meets the seals evenly. Typically, there’s a draught at the top corner on the lock side. Our guide to dropped uPVC doors explains the warning signs.

Worn hinges

Tired friction hinges let the sash sit loose on the hinge side. So, even with good gaskets, the window can’t pull tight.

Door extras

Letterboxes, keyholes, cat flaps and worn threshold seals are all common culprits on doors. Fortunately, they’re usually the cheapest to fix.

For instance, an internal letterbox brush, a keyhole cover and a new threshold strip together cost little. Yet they make a noticeable difference in a cold hallway.

Gaps around the frame

Sometimes the draught isn’t in the window at all. Instead, it comes through cracked or missing sealant between the frame and the wall.

How cold draughts are fixed

Once you know the cause, the fix is usually straightforward. Here are typical UK prices in 2026.

Cause	Fix	Typical cost	DIY?
Shrunken gaskets	Replace the gaskets	£40–£100 per window	Sometimes
Loose compression	Adjust the locking cams	Often a few minutes	Yes, with care
Dropped sash or door	Hinge adjustment or re-packing	£60–£150	Professional
Worn hinges	Replace friction hinges	£70–£150 per pair	Professional
Letterbox draught	Internal brush or flap	£10–£25 for the part	Yes
Worn threshold seal	New seal or brush strip	£20–£80	Sometimes
Gap around the frame	Re-seal with silicone	£40–£120 per window	Sometimes

For context, these are small sums next to a new window or door. That’s why it’s worth fixing cold draughts rather than living with them.

A typical draughty bedroom window, for example, might need new gaskets and a cam adjustment. That’s often a single short visit, with no mess and no change to the glass.

DIY or call a professional?

Some fixes are easy. For example, fitting a letterbox brush, adding a threshold strip or easing locking cams are all reasonable DIY jobs.

Others need experience. Gaskets come in many profiles, so the wrong one won’t seal properly. Similarly, hinge replacement and re-packing a dropped door are best left to a professional.

Avoid self-adhesive foam strips on uPVC windows. They can stop the sash closing properly and strain the locks.

Adjusting locking cams safely

1. Open the window and find the round or oval cams along the locking edge.
2. Photograph each one, so you can return it to where it was.
3. Turn every cam by the same small amount towards the tighter setting.
4. Close and lock the window, then repeat the paper test.
5. If the handle becomes stiff, ease the cams back slightly.

Draughts, ventilation and condensation

Draught-proofing and ventilation go hand in hand. Once you’ve stopped the uncontrolled draughts, keep the controlled ventilation working.

• Leave trickle vents open, at least partly, especially in bedrooms.
• Run extractor fans in kitchens and bathrooms.
• Repair any trickle vent that’s broken or stuck, rather than blocking it.

If condensation increases after draught-proofing, ventilation is the answer, not opening up the gaps again. We also install, clean and repair trickle vents.

Quick answers

Why do my windows feel draughty when they’re shut?

Usually, worn gaskets or loose compression are to blame. A dropped sash can do it too.

Can gaskets be replaced without new windows?

Yes. Gaskets can be replaced on their own, as long as the right profile is used. It’s one of the cheapest ways to fix cold draughts.

Is it a draught, or just cold glass?

Old or failed units can make the glass very cold. Air cools against it and falls, which feels like a draught. If so, see our misted double glazing repairs page.

Should I block my trickle vents?

No. They provide the steady ventilation that controls condensation and mould. If one is broken, get it repaired instead.

When is the best time to fix draughts?

Early autumn is ideal. You’ll feel the benefit all winter, and gaskets are easier to fit when the weather is mild.

Stop the draughts before winter

Cold draughts are rarely a reason to replace windows. A new gasket, a small adjustment or a hinge repair usually solves them for a fraction of the cost.

We fix draughts across the area, including window repairs in Mytchett and Deepcut. See our areas we cover page, our window repair cost guide or our full list of window and door services.