Q&A / 

Condensation on New Windows

DEAR TIM: I am at my wits end. The new replacement windows in our home are fogging up and some have dripping water on the inside pane of glass. I thought by buying new windows I would eliminate condensation forever. Are the windows defective? What is happening and what, if anything, can be done to minimize the problem? Pamela S., Gatlinburg, TN

DEAR PAMELA: The condensation on your new windows is very unfortunate. The source of the problem is not easy to trace and to make matters worse, there can be multiple things that are happening that can contribute to the problem. It is my opinion that you will solve the problem using old-fashioned detective work that employs the process of elimination.

Let's start the investigation by reviewing what causes condensation on windows, in crawlspaces, on air conditioning ducts and even in attics. The air inside your home contains moisture. It is invisible water vapor, but it is there. You and all of the people in your family contribute to this moisture each time you exhale. Try fogging a mirror with your breath and you will see what I mean.

 Installing new windows does not guarantee that your condensation problems will disappear. PHOTO CREDIT: Kathy Carter

Installing new windows does not guarantee that your condensation problems will disappear. PHOTO CREDIT: Kathy Carter

Lots of other things around your home also contribute to the addition of water vapor in the air. Uncovered ground in crawlspaces, indoor plants, laundry hung out to dry, cooking activities, aquariums, humidifiers, etc. all add water vapor to the air. Add to this the natural humidity that Mother Nature contributes to the air all around us and you can see that humidity is a very common thing.

The amount of humidity in the air can rise and fall depending upon the temperature of the air. Warm or hot air has the ability to hold much more water vapor than cool or cold air. So the humidity in air is relative. Relative humidity is defined as the percentage of water vapor in a given amount of air at a given temperature. When this percentage gets to 100 percent, the water vapor, a gas, changes from a gas to a liquid. Meteorologists refer to this complete saturation as the dew point.

Water is forming on your new windows because one of several things is happening. The temperature of the inner glass surface is at or below the dew point for the amount of humidity in your inside air. The humidity of your indoor air is quite possibly much higher now with your new windows because the air leaks around your old windows were eliminated once the new windows were installed. Cold, drier air that leaks into homes from the outdoors lowers the relative humidity indoors. This is one reason people have static electricity problems in drafty homes during the winter months. Dry air makes it very easy for the static sparks to transfer from your hands to grounded objects.

I suggest you purchase a decent hygrometer for under $50.00. This tool will allow you to get accurate readings of indoor humidity. Start to take daily readings and then look around to see if you have things that add too much water to the air. Make sure crawlspace soil is covered with high-performance vapor retarders. Minimize the number of indoor plants you might have. Run kitchen exhaust fans if you boil lots of water when you cook. If you have a vent-free fireplace, limit its use as it produces vast amounts of water vapor when it burns natural gas. Be sure to operate bathroom exhaust fans during bathing activities and pipe this humid air directly to the outdoors.

If you discover that your indoor humidity is not too high using your hygrometer, then you can minimize or eliminate the condensation by creating air movement around the windows. Just as blowing air dries say laundry things outdoors, air blowing over the interior glass will act just like the defroster does in your automobile.

Efforts to stop air leakage into homes can create all sorts of secondary effects. One of them is potential increases in indoor relative humidity levels. Indoor air pollution levels can also rise. Tightly-constructed new homes or older homes where energy-savings measures are employed create situations where little fresh air enters a home to equalize humidity and freshness.

Not all windows are made to the same standards. Some new windows may use poor-quality parts and poor construction methods that allow the glass temperature of the inner pane of glass to be much cooler than a well-built window. The cooler pane of glass will show condensation before a warmer pane of glass. This is why an empty drinking glass on a kitchen counter or a piece of glass in a picture frame has no condensation while a window two feet away is fogged up or dripping with water.

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5 Responses to Condensation on New Windows

  1. Im having horrible condensation problems on all windows primarily iny master. The window ledge wood is starting to warp from the condensation and mold is forming between the frames. My house is less than 3 years old. The master seems to be the hottest in the summer and coldest in the winter compared to the rest of the house. What would be the best way to resolve my issue?

  2. Installed a new Pella Thermastar slider for a egress window in the basement. The window is still not trimmed out on the inside because we are still framing, etc. we had two days of rain and we noticed that we had water under the vinyl sill of the window in both lower right and left hand corners. When you ran your finger under the sill in would get wet, but it is not wet enough for the water to drip onto the framing under the sill. We can not figure out what is causing this, a leak, condensation, or what? We are afraid to drywall around the window and finish the room because we can not figure out what is wrong.

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