Will your windows drip this week?
Put in your postcode and your window type. We check the weather for your street each night and work out when your glass will steam up. It takes about ten seconds.
Check my windowsYour condensation forecast
The same week with other glass
| Glass | Wet nights | Bar |
|---|
Estimates only, for the middle of the glass. Frames, edges, curtains and how you use the room change the real result.
Fed up of wiping windows every morning?
Our team can check your windows, seals and vents on a free home survey and tell you honestly what would help.
Five free ways to cut condensation tonight
You don't need new windows to make a difference. Try these first. They cost nothing.
Open the trickle vents
The small slots at the top of your frames let damp air out all night. Keep them open, even in winter.
Run the extractor fan longer
Leave the bathroom or kitchen fan on for 15 minutes after a shower or cooking. Shut the door while you do.
Dry washing outside or vented
One load drying indoors can put litres of water into the air. Use a vented dryer or a room with a window open.
Wipe the glass each morning
Water left on sills soaks into seals and plaster and can lead to black mould. A squeegee takes a minute.
Keep heat low and steady
A room kept gently warm all night steams up less than one that gets cold and then heated hard in the morning.
Mist between the panes?
That isn't the weather. It usually means the seal has failed. We can look at it on a free survey.
How the forecast works
Water forms on glass when the glass is colder than the dew point of the room air. The dew point depends on how warm and how damp the room is.
How cold the inside of your glass gets depends on two things: how cold it is outside, and how much heat your glass lets through. Old single glass lets through about four times more heat than modern A-rated double glazing. So its inner pane gets much colder.
For every hour from 6pm to 8am, we take the forecast outside temperature for your postcode. We work out the glass temperature, compare it with the dew point, and count the hours it would be wet.
The numbers we use
Inner glass temperature = room temp − U × 0.13 × (room temp − outside temp). The 0.13 is the standard inside surface resistance used in UK building calculations.
Centre-of-glass U-values (W/m²K): single 5.8 · older double 2.8 · A-rated double 1.4 · triple 0.8. These are typical figures; your actual glass may differ.
Dew point uses the Magnus formula. "Normal" air = 60% humidity, "damp" = 70%, "very damp" = 80%.
A night counts as wet at 3+ hours of condensation, misty at 1–2 hours.
Weather data by Open-Meteo.com (CC BY 4.0). Postcode lookup by postcodes.io, contains OS data © Crown copyright and database right.
Questions about condensation
Why do my windows get condensation on the inside?
Warm, damp room air touches cold glass. When the glass is colder than the air's dew point, water comes out of the air as droplets. Cold nights, damp air and poorly insulated glass make it worse.
Will new double glazing stop condensation?
Modern A-rated glass keeps the inner pane much warmer, so it steams up on far fewer nights. It won't fix a very damp home on its own. Good ventilation, trickle vents and extractor fans still matter.
What does condensation between the two panes mean?
Misting between the panes isn't weather. It usually means the seal on the sealed unit has failed and the unit needs replacing.
How accurate is this forecast?
It's an estimate. It uses the hourly weather forecast for your area and standard figures for how much heat each glass type lets through, measured at the centre of the glass. Frames, edges, curtains and how you use the room all change the real result.