Condensation!!! Help me understand....my windows are new.

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.

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. 

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

Your indoor humidity is too high and/or the exterior temperature is so cold it is dropping the temperature of the inner pane of glass *below* the dew point of the air inside the house. This is easy to test. TURN OFF all sources of interior humidity. Here is a list that can contribute to indoor humidity and condensation, 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.

 By Tim Carter (Ask the Builder)

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