How To Prevent Frost On Windows

If you are waking up to frost on your window glass, it may be beautiful to look at, but you need to do something to correct this problem.

Baby, Its Cold Outside!

Frost is caused by warm, moist air inside the house coming in contact with the cold window glass. The glass surface is the coldest surface on the exterior wall and where the warm air is going to attach. By nature the relative humidity wants to balance itself out. Warm, moist air inside, trying to balance with the cold air outside, attaches to the glass as condensation and turns to ice, creating frost.

Outdoor Temperature to Recommended Indoor Relative Humidity

Temperature Outdoors Indoor Relative Humidity
+20° F. 35%
+10° F. 30%
0° F. 25%
-10° F. 20%
-20° F.. 15%
+10° F. 30%
Source: Anne Field, Extension Specialist, Emeritus, with reference from the Association for Home Appliance Manufacturers (


When the frost melts, it will drip down on the window trim and casings and cause the woodwork to deteriorate, or leave mold and black residue that can lead to rotted woodwork or allergies.

Preventing Window Frost

  • Decrease the Relative Humidly in the house: Run a dehumidifier in the house to pull moisture out of the air and Decrease the temperature by a few degrees.
  • Increase Airflow: Run a ceiling fan in room, or and oscilating fan to circulate the air.
  • Leave the Blinds Up. If you have blinds, trying leaving them up 6-10 inches from the bottom; this will allow air to flow more freely around them, instead of becoming trapped behind the blinds.
  • Add a Layer of Airspace. Consider exterior storm windows or interior plastic wrapping.
  • Add an Air Exchanger. This will allow you to control the humidity in the house through your heating and cooling system.

Any combination of these tips may help prevent frost on your windows.