Controlling Window Condensation

Thursday, April 03, 2014  

Extreme weather conditions can lead to increased issues of condensation within a home. Condensation may be found on metal or glass surfaces, especially surfaces near wall openings, such as windows and doors.

The risk of condensation inside the home is directly related to the outside temperature and the level of humidity within the home. Based on a 70ºF interior room temperature, engineering studies have established the following recommendations for indoor humidity levels for given outside temperatures:

Outside Temperature (F) Relative Humidity (%)
20-40 > 40%
10-20 > 35%
0-10 > 30%
-10-0 > 25%
Below -20 > 20%

These guidelines do not guarantee that condensation will not appear on mirrors or windows. Factors such as closed blinds or drapes may require you to decrease the relative humidity in your house below these guidelines.

A good rule of thumb for controlling relative humidity in the winter: 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 adjust the humidistat and HRV setting to properly control the humidity in your house.

The values above may need to be adjusted based on many factors, including tightness of the home, inside temperature, heating system, and building materials.

Here are a few methods to help control the humidity within the home:

  • Utilize vents and exhaust fans in areas where humidity is created – including showers, baths, laundry and cooking – to remove humid air to the exterior. Continue ventilation until humidity levels are lowered.
  • For tight homes with low infiltration, install an outside air intake damper system – preferably with heat exchanger to the heating system.
  • Confirm crawl spaces and attics have proper ventilation.

There are several steps you can take to help reduce the overall risk of condensation in your home:

  • Install high efficiency windows and doors.
  • Ensure heat registers are not blocked by rugs or furniture.
  • Create air movement on glass and metal surfaces by opening curtains and/or utilizing ceiling fans in reverse mode.
  • Use caulk and weather stripping to eliminate outside air infiltration.
  • Confirm windows and doors close tight and without drafts.
  • Install storm windows and doors or plastic thermal coverings on inefficient windows and doors.
  • Maintain humidity levels based on the guidelines above.

There are many websites and videos addressing window condensation. One site that is particularly helpful is from Home Energy Resource MN.

Please see Windsor Care & Use Guides for additional information regarding specific products...



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