What’s Causing Condensation on my Windows?

Anything from the steam that escapes when you open the dishwasher to boiling water on the stove can cause condensation. Moisture from a hot shower, steaming kettle or even washing the dishes can create condensation on your windows, mirrors and walls.

You may be surprised to learn how much water vapor is created in a home on a daily basis. An average-sized family can add a half pint of water vapor every hour to the home through breathing and perspiration. If you take a five-minute shower, you produce another half pint of water vapor. The act of cooking dinner can produce two and a half pints of water vapor inside your home.
To minimize condensation in your home…

  • Use kitchen and bathroom exhaust fans.
  • In addition to exhaust fans, open a window in the bathroom to increase ventilation.
  • Properly vent clothes dryers, gas appliances and stoves.
  •  Make sure your attic and basement or crawl space is well ventilated.
  •  Open curtains and blinds to allow more air circulation around your windows.
  • Store firewood outside. Wood holds moisture that can be released into your home.
  • If you have a humidifier, set it to the correct outside temperature. If you have a damp basement, use a dehumidifier.

Outside Temperature                   Inside Humidity

 0º to 10ºF                                             Not over 30%

 -20º to –10ºF                                      Not over 20%

-20ºF or below                                     Not over 15%

-10º to   0ºF                                          Not over 25%

10º to 35ºF                                           Not over 35%

Engineering studies provide the following guidelines for the minimum recommended humidity levels for residential construction, based on a 70ºF interior room temperature.

Following these guidelines does not guarantee that condensation will not appear on mirrors or windows but it should dramatically improve the situation. Factors such as closed blinds or drapes may require you to decrease the relative humidity in your house below these guidelines.

If frost or condensation forms on your windows, the humidity is too high and you should turn down the humidistat.  If your hardwood floors start to separate, the humidity is too dry and you should turn up your humidistat.  You may need to regularly monitor and adjust the humidistat setting to control the humidity in your home.