The first cold snap hits!  The windows fog up and water drips down the glass.  Don’t worry, this is not and indication that your windows have failed.  The moisture on the glass is condensation, a natural occurrence that in most cases can be eliminated.  Condensation occurs when excess humidity in the air comes up against a cool surface.  The glass in windows and patio doors provides a cooler surface that can show the first signs of condensation.  This phenomenon can usually be corrected by increasing the air flow in the room.

Homes that are built today are more energy efficient and more air-tight than homes built even a few years ago.  Because of this there is less exchange with outside air.  This saves energy, but tends to increase interior humidity.  Because the humidity levels inside the home tend to rise, you may notice condensation in your new home that you never had in your old home.

Older homes with newer windows may experience condensation due to increased efficiency.  Old windows allowed a lot of air exchange with outside, allowing the inside air to dry out.  New windows are installed in an airtight manner, which is great, but it traps humid air inside.

Why is there so much humidity?  Family lifestyle has the most impact.  Cooking meals, long showers or baths, even washing clothes all contribute to humidity levels.  People often experience the condensation in a bedroom where they spend a lot of time.  Variations in these and other moisture generating activities or products (like a humidifier) can result in one neighbor experiencing condensation and another not.

What can we do?  Controlling indoor humidity is the key.

  • If you don’t already have new windows, consider installing a window that has a dual paned insulated glass unit.  For further protection, we always recommend getting windows with an insulated glass unit that includes a Low-E coating.  This coating on the glass reduces radiant heat-loss and the passage of ultraviolet rays.  The better the Low-E the more it stops condensation.  A ‘soft coat’ Low-E is the best.
  •  Having windows that include Argon gas between the panes helps out as well.  Since Argon is an inert gas, and heavier than air, it makes a great buffer for heat transfer.  Having windows that have both Low-E and Argon gas is the way to go for energy efficiency.  Look for the Star.  Energy Star rated windows will have an NFRC rating sticker that will tell you the efficiency ratings for the window.

  • You can raise the temperature of your home.  Even just one or two degrees can make a difference and greatly reduce condensation.
  • Open your blinds or curtains for air circulation.  Closed blinds or drapes trap warm air in the space between the glass and the blinds.  This air cools and releases moisture.  Blinds should be at least 4” away from window glass.
  • Use a ceiling fan to move warm air toward your windows.
  • For an unoccupied or unheated room, keep interior doors open to promote air circulation.
  • Run the exhaust fans in bathrooms and kitchens.
  • Make sure all vents and ducts are clear of lint and other obstructions.
  • There are some causes why the condensation may be only temporary as well.  If it is a new home, building materials in construction contribute gallons of water to the inside air.  It often takes a whole year for all that moisture to escape.  Condensation can also be a problem during the first few weeks you run your heater.  This is due to the release of moisture the house has absorbed during the summer.  Quick temperature changes can also be a cause of condensation.

If you have excessive condensation in your house, it is important to measure your humidity.  Very high interior humidity can leave to structural damage to your home (wood decay) and even health hazards such as mold growth.  Because these effects usually happen unseen in the wall cavity, condensation on the windows is a good clue that the humidity is too high.  Get a hygrometer, an instrument that measures relative humidity in the air, to monitor indoor levels.  If high condensation persists after trying some of the above remedies, contact a qualified heating and air conditioning professional.

Aluminum windows are especially subject to condensation because of its ability to transfer heat.  The temperature of aluminum will quickly change to the air temperature around it.  An aluminum window including a thermal break has a much lower chance of condensation.  Vinyl windows are the least susceptible to the condensation phenomenon.

Condensation is a natural occurrence that happens on the exterior and interior glass surfaces.  In nearly all cases, it is not the result of a defective window or patio door.  Take steps to reduce humidity with proper air circulation and the problem should be solved!