How to Fix Condensation on Windows

Waking up to windows running with water is a common sight, especially in colder months — and in most cases it’s a sign of too much moisture in the air rather than a fault with the window. Condensation forms when warm, humid air meets a cold surface, and where it appears tells you what’s causing it and how to fix it.

The Three Types of Window Condensation

Knowing which type you have is the whole battle. Condensation on the inside surface of the glass means there’s too much humidity indoors — this is the most common and the most fixable. Condensation on the outside surface is actually a sign your windows are well insulated; it’s harmless and clears as the sun warms the glass. Condensation trapped between the panes of a double-glazed unit is different — it means the seal has failed and the unit needs replacing.

Why Interior Condensation Happens

Everyday life adds a lot of moisture to indoor air: cooking, showering, drying laundry, even breathing. When that humid air meets cold glass, the moisture condenses into water droplets. Poor ventilation lets humidity build up, and single-pane or poorly insulated windows give the moisture a cold surface to settle on.

What You’ll Need

Much of the fix is about managing moisture and airflow rather than tools. A simple hygrometer lets you measure indoor humidity, and a dehumidifier is the most effective way to bring it down in problem rooms. For cold glass, window insulation film raises the surface temperature so moisture is less likely to form.

Fix 1: Reduce Indoor Humidity

Tackle the moisture at the source. Run the extractor fan when cooking and showering, and keep lids on pots. Vent your tumble dryer outside rather than into the room, and avoid drying laundry indoors where you can. Aim to keep indoor humidity somewhere between 30 and 50 percent — a cheap hygrometer shows you where you stand.

Fix 2: Improve Ventilation

Stale, trapped air holds moisture. Open windows for a few minutes each day to let damp air out and fresh air in, open any trickle vents built into the frames, and make sure air can circulate — don’t push furniture tight against exterior walls or block vents with long curtains.

Fix 3: Warm the Glass Surface

Because condensation forms on cold surfaces, anything that keeps the glass warmer helps. Applying window insulation film creates an insulating layer, thermal or heavier curtains reduce the chill on the glass, and upgrading single glazing to double glazing solves it for good over the long term.

Fix 4: Use a Dehumidifier

In rooms that stay damp — bedrooms overnight are common — a dehumidifier pulls moisture straight out of the air and is the quickest way to stop condensation forming on the windows.

Fix 5: Fogging Between the Panes

If the misting is trapped inside a sealed double-glazed unit, no amount of ventilation will fix it. The seal has failed and the unit has lost its insulating properties, so the glass unit itself must be replaced — a job for a glazier.

How Much Does It Cost?

Reducing humidity and improving ventilation cost nothing. A dehumidifier runs roughly $30 to $150, window insulation film is $10 to $20, and replacing a failed sealed glass unit typically costs $150 to $400 per window.

When to Call a Professional

Bring in help if you have fogging between the panes (which needs a glazier), or if persistent condensation has led to damp, mould, or rot around the window frames. Ongoing moisture problems are worth addressing properly, both for the house and your health.

A Note on Mould

Persistent condensation feeds mould growth on frames, sills, and walls, which can affect indoor air quality and health. If you’re seeing black spotting around the windows, treat the condensation as a priority rather than just wiping the glass each morning.

Frequently Asked Questions

Why do my windows get so much condensation?

There’s more moisture in your indoor air than the ventilation can clear, and it condenses when it meets the cold glass. Cooking, showering, drying laundry indoors, and poor airflow all add to it.

Is condensation on windows bad?

Interior condensation isn’t harmful in itself, but left unchecked it can lead to damp and mould around the frames. Exterior condensation is harmless. Fogging between the panes signals a failed window seal.

How do I stop condensation on windows overnight?

Lower the humidity in the bedroom — crack a window or open a trickle vent, run a dehumidifier, and avoid drying clothes in the room. Keeping the door open to improve air circulation also helps.

Why is there condensation between my double-glazed panes?

The seal around the sealed glass unit has failed, letting moist air in between the panes. This can’t be fixed by controlling humidity; the glass unit needs to be replaced.

Does a dehumidifier stop window condensation?

Yes. By removing moisture from the air, a dehumidifier reduces the humidity that condenses on cold glass, making it one of the most effective fixes for interior condensation.