Doors & windows

Condensation on the inside of windows

Water dripping down the inside of your windows on cold mornings means the air inside is carrying more moisture than the cold glass can handle. A little now and then is normal. Every day, and puddling on the sills, means the house is too humid, which can lead to mold and rotted window frames. Lowering the humidity is usually the fix. A ten-dollar humidity monitor settles most of these arguments in a day.

Wiping fog off the inside of a cold window while holding a hygrometer
Fog on the inside of the glass means the air indoors is too humid.
Quick answerMeasure the indoor humidity and aim for 30 to 50 percent. Run exhaust fans, cut back on moisture, open the blinds and keep vents clear. Fog between the panes means a failed seal instead.
Worth checking firstWipe the glass. If the water won't wipe off, it's between the panes and humidity isn't the problem.

Good to knowRenter-friendlyGood first repairNo toolbox needed

Mike TurnerWritten and reviewed byMike TurnerUpdated Sources and safety notes
Easy15–30 min$0–30
A room in winter: warm, moist air from cooking and showers meeting a cold window and condensing into droplets that run down to the sill, a humidity monitor reading 62 percent, closed blinds trapping cold air at the glass, an exhaust fan, and a close-up of fog between two panes of glass.
Cold glass (1) chills the moist indoor air (2) until water condenses and runs down to the sill (3). High humidity (4) is the root cause, and exhaust fans (5) remove it. Fog between the panes (6) means a failed seal instead.

Why windows sweat

Warm air holds more moisture than cold air. When indoor air touches cold glass, it cools and the moisture condenses into droplets, the same way a cold drink sweats in summer. The colder it is outside, the lower the indoor humidity needs to be to keep the glass dry.

Condensation on the outside of the glass is normal, especially on efficient windows. Fog between the panes of a double-pane window means the seal has failed, and that can't be wiped or fixed from the inside.

Where the moisture comes from

High indoor humidity

Cooking, showers, laundry and people.

Cold glass

Single-pane or older windows get coldest.

Poor air flow

Blinds and furniture trap cold air at the glass.

A humidifier set too high

Too much moisture for cold weather.

Where is the water?
It's onWhat it meansWhat to do
The inside surfaceHumidity is too highLower the humidity; run fans.
Between the panesThe seal has failedReplace the glass unit.
The outside surfaceNormal, often efficient glassNothing.
The sills, with dark spotsWater is sittingWipe, dry and check for rot.
Don't let it sitWipe standing water off the sills every day until the humidity is down. Left sitting, it soaks into wood frames.

Let's fix it

0 of 6 done
  1. See which side it's onWipe the glass. If it wipes off, the moisture is on the inside surface and humidity is the problem. If it's between the panes, the window's seal has failed. If it's outside, it's normal.
    Something went wrong?
    • The fog is between the panes The seal has failed. The glass unit needs replacing.
    Finger wiping droplets off the inside of the glass, compared with fog trapped between the panes
  2. Measure the humidityPut a humidity monitor in the room for a day. Indoor humidity between 30 and 50 percent is a good range, and in very cold weather you may need to stay near the lower end to keep windows dry.
    Humidity monitor on a shelf reading 38 percent, inside the 30 to 50 percent range
  3. Run the exhaust fansRun the bathroom fan during showers and for about 20 minutes after, and the kitchen hood while you cook. Make sure the dryer vents outside.
    Bathroom fan and kitchen range hood running with moist air leaving the house
  4. Cut back on moistureTurn down or turn off any humidifier. Cover pots while cooking, move plants away from windows, and don't dry laundry indoors. Run a dehumidifier in a damp basement.
    Humidifier turned down, a lid on a boiling pot and plants moved away from the window
  5. Keep air moving at the glassOpen blinds and curtains during the day so warm room air reaches the glass. Don't block the heat vents under windows, and run ceiling fans on low.
    Blinds opened and a heat vent under the window left clear so warm air reaches the glass
  6. Wipe it and check the sillsWipe off any water every morning until it stops. Check the sills and frames for dark spots or soft wood. Clean small mold spots with detergent and water and let them dry.
    Something went wrong?
    • The sill is soft or mold keeps coming back Stop there. Soft wood means rot, so have a window pro check the frame.
    Towel wiping water off a window sill and a small dark mold spot being checked

Watch it done

What Causes Window Condensation and How to Stop ItBy American Window Concepts on YouTube. Their method may vary a little from ours.
Watch on YouTube
How you'll know it's fixed
  • The glass stays clear in the morning
  • The humidity monitor reads in the 30 to 50 percent range
  • Sills and frames stay dry, with no new dark spots

Still fogging with good humidity? Consider storm windows or film.

If they still fog up

If condensation keeps forming with humidity in a good range, the windows may be single-pane or poorly sealed. Storm windows or window insulation film help a lot.

If only one window fogs up, check what's near it: a bathroom, a kitchen, a fish tank or plants.

Watch the humidityA cheap humidity monitor tells you right away whether a change is working. Keep an eye on it as the weather gets colder.
Renting?If you rent, run the fans and watch the humidity, and tell your landlord about fogged glass or rotting sills.
Get help ifThere's fog between the panes, the sills or frames are soft or rotting, mold keeps coming back, or the whole house stays humid even with fans and a dehumidifier running.Fix it yourself or call? Compare the cost →

What a pro typically charges (a rough estimate; prices vary by area): Replacing a fogged double-pane glass unit typically costs $150–$500 per window. Whole-house ventilation or dehumidifier work varies widely.

Find a handyman near you

Something else going on?

Window condensation questions

Is condensation on the inside of windows bad?

A little on cold mornings is normal. Every day, or water pooling on sills, means the house is too humid and can lead to mold and rot.

What indoor humidity stops window condensation?

Aim for 30 to 50 percent, and closer to the low end in very cold weather.

Why is there fog between my window panes?

The seal between the panes has failed. The glass unit needs replacing.

Does opening blinds help with condensation?

Yes. It lets warm room air reach the glass so it stays warmer and drier.

Why are my windows wet on the inside?

The air inside is carrying more moisture than the cold glass can handle. Lowering the indoor humidity is usually the fix.

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About the authors

GrabTheHammer Team

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  • Safety first
  • Tells you when to call a pro

We're a small team of writers and editors who check every guide against manufacturer instructions and common code requirements. Our goal is to help you understand the problem, tackle what you safely can and know when to call a pro.

Checked against: Manufacturer instructions for the parts and products involved, EPA mold guidance, U.S. Department of Energy.

How we write and review →
A helpful next stepReplace a broken window paneClean up safely, remove the old glass and glazing putty, measure and cut or order new glass, set it with glazier's points, and finish with fresh glazing compound and paint.