How to Avoid and Remove Window Condensation

Updated: Feb. 26, 2024

Condensation forming on your windows in winter? Luckily, this problem is usually simple to solve. Read on to learn what to do.

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Are your windows fogging up with condensation during the heating season as outdoor temperatures drop? If so, you're not the only one. Condensation on windows is a common issue in areas where below-freezing winter temperatures are the norm.

The reason boils down to modern house construction. Because new homes are much better sealed than they used to be, natural ventilation to the outdoors is much lower than in their drafty predecessors.

So how does this lead to window condensation? It all comes down to the relative humidity of the air. Ideally, it should hover around 50 to 55 percent. If it's higher — say, 60 or 70 percent — your windows will become dehumidifiers and condense water from the warm, moist indoor air until the relative humidity drops.

Window condensation indicates poor indoor air quality. If left unchecked, it can lead to mold, mildew, structural damage and health issues. We'll answer some common questions about this unwanted moisture, then tell you how to avoid and remove it.

For this article I consulted my father-in-law, Walenty Bednarksi, who earns his living testing indoor air quality and tackling the installations to improve it.

Does a cold house cause condensation?

"Not entirely, but it's a contributing factor," says Bednarski. "Colder indoor air is closer to the dew point." That means the air can no longer hold water vapor, which condenses into liquid.

Colder indoor space also means your windows will be colder, speeding the air toward the dew point.

What's the fastest way to remove condensation from your windows?

Increase ventilation in your home and crank up the heat.

Should you wipe condensation off your windows?

Yes. "The longer condensation remains on the windows, the more likely mold and mildew will start growing," Bednarski says. However, that still doesn't address poor ventilation.

What temperature should I keep my house to prevent condensation?

As warm as you comfortably can. Warmer indoor air means warmer window glass, and warm glass won't cool indoor air as quickly. That reduces the likelihood water vapor will condense.

Does vinegar keep condensation off windows?

No. "Vinegar can help clear away water marks and mold caused by condensation," Bednarski says, "but it does absolutely nothing to stop it from forming in the first place."

When to call a pro

Consider calling a heat recovery ventilator (HRV) installation pro if opening windows, running exhaust fans and keeping your home warmer doesn't solve the problem. HRV's bring in fresh outdoor air, preheating it with the warmth from your home before getting rid of moist indoor air.

"Even though they're not cheap

Tools Required

  • A hygrometer

Project step-by-step (5)

Step 1

Evaluate your home’s relative humidity

  • Examine all your windows for condensation. If you find some, your indoor air is too humid and further steps are needed.
  • Purchase a hygrometer to measure the relative humidity of the air in your home. It should be between 50 and 55 percent. Any more than this and condensation could start forming on your windows, if it hasn’t already.
  • Take note of spikes in relative humidity. Burning propane and natural gas in fireplaces releases moisture into the air, as does keeping a lot of house plants. Use the hygrometer to become aware of the activities that cause window condensation.
Step 2

Crack open a few windows

  • Open at least one window on each floor an inch or two. Even in the depths of Canadian winters, I always leave a window or two on each story of my house slightly cracked. The heat loss is insignificant, and the fresh, dry air from outside prevents condensation before it starts.
  • Take note of any particularly wet windows. Crack these open first, then wait a day or two to see if the fresh air halts the condensation.
  • If your home is new, try opening your door for 10 to 15 minutes on cold evenings. New concrete, wood and other materials usually take 12 to 18 months to dry, and the drying-out process could be partly responsible for your window condensation.

Opening the window during winterssUs_angel/ Getty Images

Step 3

Run indoor exhaust fans

  • Check your bathroom(s) for switch-controlled exhaust fans.
  • Let them run for a least an hour a day. If window condensation persists, run them longer.
  • Be sure to run your fan during all baths and showers, and for at least 20 minutes after the water stops running.

A man setting up the exhaust fan Sadeugra/Getty Images

Step 4

Crank up the heat

  • Try increasing your thermostat’s set point for a few days.
  • Make note of any changes to the amount of condensation on your windows.
  • Note the changes in relative humidity using your hygrometer.

A woman setting temperature in thermostatWestend61/Getty Images

Step 5

Install an HRV

  • Call a reputable HRV installer if you’ve tried all the steps above and still have a moisture issue.
  • Be sure to discuss the correct size of HRV for your home, along with the ideal location for the unit and the vents connecting it to the outside.