As winter nears, you may be experiencing colder weather conditions and falling temperatures. A common side effect of seasonal change is the appearance of frosty or foggy windows. Don’t be alarmed. The quality of your windows’ manufacturing is most likely fine. Condensation is often just an indicator your home’s humidity levels are too high.

What is condensation?

Condensation is water that collects on a surface when humid air comes in contact with a colder substrate, such as glass. Due to the temperature change, water vapor is converting from a gas to a liquid. Sweaty, foggy, frosted or icy windows are all forms of condensation.

What causes condensation?

Today's tighter, more energy efficient homes can increase indoor humidity. Older homes had random gaps, which allowed for the release of warm, moist air and the replacement of cool, drier air. Newer construction methods do not allow this natural air-to-air exchange. Any internally created humidity gets trapped inside the structure. Elevated humidity then causes condensation to form on cold surfaces, such as windows.

How can I prevent condensation?

There are many different ways to control condensation in your home:

  • Check a hygrometer.
    A hygrometer is an instrument that measures moisture content. It’s a relatively inexpensive device that can quickly help you identify humidity concerns that might be at the root of your condensation issues.
  • Reduce the use of humidifiers.
    If you use a humidifier in your home, try adjusting the levels. As a result, the humidifier will release less moisture into the air, which will hopefully reduce condensation.
  • Turn on bathroom and kitchen fans.
    If you’ve ever seen a foggy bathroom mirror or pot lid, you know that activities like showering and cooking release a lot of moisture into the air. Be sure to run hoods and exhaust fans for a brief time after bathroom or kitchen activities.
  • Circulate the air.
    Air movement helps reduce the condensation on your windows. It’s good practice to continue using ceiling fans in the winter. Be sure to set your fans to clockwise rotation — this will push warm air from the ceiling down to the floor.
  • Adjust your thermostat.
    A slight bump in your house’s heating system may help raise the temperature of your windows and reduce or eliminate condensation.
  • Utilize window treatments.
    You can also use blinds, curtains, drapes and other window treatments to moderate window temperatures as well. Opening curtains while your furnace is running, for example, will allow warm air to circulate around windows.
  • Relocate your plants.
    Plants release moisture into the air. If you have several plants by your windows, try moving them to a different spot in the house to help reduce condensation.
  • Install an air-to-air exchanger.
    An air-to-air exchanger removes moisture by bringing in fresh air from the outside while sending indoor air outside, as well as potential airborne pollutants.

What are desired levels of humidity?

The chart below illustrates recommended winter humidity levels:

Outdoor Temperature :: Indoor Humidity at 70° F

  • -20 degrees F or below = not over 15%
  • -20 degrees F to -10 degrees F = not over 20%
  • -10 degrees F to 0 degrees F = not over 25%
  • 0 degrees F to +10 degrees F = not over 30%
  • +10 degrees F to +35 degrees F = not over 35%

These are only recommended humidity levels, and may not be applicable for every household. Differences in glass types (LoE vs. clear) will allow for variances in humidity levels.