Getting Rid of Condensation

What are the causes and consequences of frosty window panes?  Should the problem be addressed, and if so how?

Condensation forms when indoor moisture makes contact with the cool glass surface and in sub-zero temperatures ice may appear.  Occasional light condensation and frost does not pose a problem.  However, excessive amounts persisting over long periods can cause major damage to your window frame and wall below.

The first step in tackling excessive condensation is to control the relative humidity (RH) and moisture sources in your home.  RH is the ratio of the amount of moisture in the air at a specific temperature to the maximum capacity of the air at that temperature.  No matter how dry the air feels it still contains some moisture, and the colder it is outside the greater the potential of indoor moisture turning to ice on the window.  Here are a few easy ways to control excessive moisture.

• Avoid drying clothes indoors
  
  
• Avoid bringing fresh wood inside to dry
  
  
• Use your kitchen and bathroom vent fans to extract moisture to the outdoors
  
  
• Routine annual inspection of all fuel burning appliances

If you want to measure the relative humidity inside your home, use a hygrometer.  RH levels vary depending on the window type.  The following chart, based on double-glazed windows, offers a guideline for RH levels at various outdoor temperatures.

A furnace humidifier helps control moisture levels inside the home.  If you’ve tried controlling your moisture levels and still experience problems, additional ventilation may be required.

One possible solution is the installation of a Heat Recovery Ventilator (HRV), a device which exhausts stale, moist air to the outdoor and brings in frsh air to distribute through existing ductwork.  HRVs are expensive but they are very energy efficient to operate.

Excessive frosting on windows may also mean it’s time to replace poor-performing windows with warmer energy-efficient ones.  Replacing old windows may eliminate the need for controlled ventilation altogether.

If you cannot afford better windows, consider placing shrink-wrap over your existing windows during the winter months.  Installation kits can be purchased at homebuilding supply stores.  Temporary or permanent storm windows are another option.

Make the following inspections if the frosted window is an isolated case.

• Check for air leaks with an incense stick or a thin piece of plastic.  Plug leaks with an air sealant on the warm side of the window.
  
  
• Check to make sure the heat register under the window is not blocked.
  
  
• Draw your drapes in the evening.  This may bring warmth to your window and even help keep valuable indoor heat from escaping.
  
  
• Relocated plants situated near the problem window(s) as plants produce quite a bit of moisture. 
  
  
• If condensation or frosting problems occur between window glazes, this means the seal is broken an the entire window may need to be replaced.