Why Is My Double Glazing Misted Up Inside the Glass?

If your double glazing has gone cloudy and you cannot wipe the mist away because it is inside the glass, you are not doing anything wrong, and you are not alone. It is one of the most common window problems we get asked about across York. The good news is that it usually has a straightforward fix, and it is often cheaper than people fear.

What the misting actually means

A double glazed unit is two panes of glass with a sealed gap between them. That gap is filled with dry air or gas and kept sealed all the way round the edge. When you see mist or water droplets between the panes, it means that seal has failed. Moisture has found its way into the gap and is condensing on the cold inner surface where you cannot reach it.

This is different from condensation on the inside of your room-facing glass, which is about humidity in the room and usually clears with better ventilation. Misting trapped between the panes is a failed sealed unit, plain and simple.

Why sealed units fail

Sealed units do not last forever, and a few things bring the end date forward:

• Age. Most units last many years, but the seal is the part that eventually gives up.
• Standing water. Blocked drainage holes in the frame let water sit against the seal.
• Heat and sun. South-facing windows expand and contract more, which stresses the seal.
• Knocks or movement. Damage during fitting or later can start a slow leak.

None of these are your fault, and a bit of misting does not mean the whole window is ruined.

The bit most people get wrong

Here is the part worth knowing before anyone quotes you for a full new window: in most cases you do not need to replace the whole thing. If the frame is sound and the hinges and locks still work, a glazier can usually replace just the failed sealed unit, keeping your existing frame. That is a much smaller job and a much smaller bill.

Replacing the whole window only really makes sense if the frame itself is damaged, very old, or you were planning to upgrade anyway. If several units around the house have gone at once, it is worth getting someone to look at the lot, because there may be a pattern worth sorting.

We cover exactly this kind of thing on our window and door repairs page, and we will always tell you honestly whether a repair or a replacement is the better call.

Can you fix misted glass yourself?

You will see "defogging" kits and drilling tricks online. We would gently steer you away from them. They rarely give a lasting result, because the real problem is the broken seal, not just the trapped moisture. Handling glazed units also has a knack to it, and a cracked pane turns a small job into a bigger one. This is a quick, low-cost job for a glazier, so it is usually not worth the risk.

FAQs

Can misted double glazing be repaired without replacing the whole window?

Usually, yes. If the frame is in good condition, a glazier can replace just the failed sealed unit and reuse your existing frame, which is far cheaper than a whole new window.

How much does it cost to replace a misted double glazed unit?

It varies with the size and glass type, but replacing a single sealed unit is one of the more affordable window jobs. Ask for a price per unit, and get the whole house looked at if more than one has gone.

Is misted double glazing a big problem?

It is mostly a cosmetic and efficiency issue rather than a safety one. The window still works, but a failed unit is not sealing or insulating as it should, so it is worth sorting rather than leaving.

Why is only one of my windows misted up?

Sealed units fail individually. One going while the others are fine is completely normal, often down to its position, sun exposure or a blocked drainage hole in that particular frame.

Got a window or two that have clouded over? Request a free quote and we will take a look across York and North Yorkshire, or download our latest brochure if you are thinking of upgrading while you are at it.