Common household condensation, or “sweating” on windows is caused by excess humidity or water vapor in a home.  When this water vapor in the air comes in contact with a cold surface such as a glass window, it turns to water droplets and is called condensation.  All homes have occasional condensation, such as a little fogging on the windows, and are no cause for concern.

On the other hand, “excessive” or “problem” window condensation, frost, peeling paint, moisture spots on ceiling and walls, water running off the windows staining woodwork and damaging the wallpaper or plaster can be signs of excessive condensation and potentially damaging problems in your home.  We tend to notice condensation on windows first because moisture doesn’t penetrate these surfaces.  It is natural to blame your windows, but you shouldn’t.  Windows don’t cause problem, simply indicators that you need to reduce the indoor humidity of your home.

All air contains a certain amount of moisture, even indoors.  And there are many common things that generate indoor humidity such as your heating system, humidifiers, cooking, bathing & showers.  In fact, every activity that involves water, even mopping the floors, contributes moisture to the air.

Heating and Ventilating magazine provides builders with reference data on sources of water vapor.  For instance, cooking for a family of four adds 4.5 lbs. of moisture a day to a house.  Each shower contributes half a pound; a weekly laundry, 30 lbs.; human occupancy, 6 – 8 lbs. per day; dishwashing 1.2 lbs. etc.  All of this moisture MUST eventually escape from your home.  So you can see that the modern living of a family of four can easily release 150 pounds, or more than 18 gallons of water per week into the air in your home!  And house with no basements have further moisture problems.

It is also very normal to experience condensation at the start of each heating season.  During the humid summer months your home absorbs moisture and then perspires when you turn on the heat.  The is only temporary though, after the first few weeks of heating you home should dry out, reducing, if not elimination condensation.

You’ll notice the same scenario if you have done some remodeling or building.  Due to high levels of moisture in wood, plaster and other building materials, your home will temporarily sweat during the first few weeks of the heating season.

Another factor in the condensation equation is progress.  With today’s modern insulation, moisture-barrier materials and air-tight construction, we all enjoy a more thermally efficient home – one that blocks the cold out, yet traps the moisture in, producing higher humidity levels and… more condensation.

The best way to reduce condensation is by eliminating excessive humidity.  So how much humidity is too much?  The following table illustrates the recommended or comfortable levels of indoor humidity during the winter months.

Inside Relative Humidity for:
Outside Air Temperature 70° F. Indoor Air Temperature
-20° F. or below                             Not over 15%
-20° F. to -10°                               Not over 20%
-10° F. to 0°                                   Not over 25 %
0° F. to 10°                                     Not over 30%
10° F. to 20°                                   Not over 35%
20°F. To 40°                                   Not over 40%

These humidity’s are in the comfortable range.  These can be measured using a humistat or psychrometer.

Seven Practical Steps to Control Condensation

1.  Put on storm windows or replace single pane windows with insulated glass.

This will better insulate your windows from the outside cold air.  Remember, moist air must contact a cold surface in order to condense.  By installing windows that maintain a warmer indoor surface you will minimize the amount of moist air that condenses on them.  This won’t prevent excess humidity in the air; but it will make looking out your windows easier.

2.  Shut off the furnace humidifier and any other humidifying devices in your home.

The process of heating your home will reduce the relative humidity, providing it’s DRY heat.  This alone will counterbalance most or all of the moisture produced by modern living.

3.  Be sure that louvers in attic or basement crawl spaces are open and that they are large enough.

4.  Run kitchen or other ventilating fans longer and more often than has been your custom.

5.  Open fireplace damper to allow easier escape for moisture.

6.  Air out your house a few minutes each day.

Airing out the kitchen, laundry and bathrooms during use, or following use can help remove excess moisture that may have built up while being used.

7.  A dehumidifier can help reduce interior condensation.

If these common remedies don’t work, you really have a condensation problem.  Because of so many variables, a condensation problem can sometimes be very tough to solve.  That’s why at this point we would recommend that you put an expert to work on your problem.  Contact a heating contractor to look at the problems.  He may suggest an outside air intake for your furnace; venting of gas burning heaters and appliances; or installation of ventilating fans.  These inexpensive options will be less costly that a major painting job or plaster work caused by excess water vapor.

The basic principle of reducing window condensation is extremely simple.  When there’s too much condensation on your windows, it means that humidity is too high in your home. You should take necessary steps to reduce humidity until condensation disappears.

While we have been discussing the control of condensation, we’ve mentioned just about everything except windows.  There’s a good reason.  There just is nothing much that can be done with windows to cut down condensation.  As the building experts have often pointed out, the windows are not to blame for condensation.  The moisture content of the inside of a home is both the cause and the cure.

With all that being said, if you happen to look at your window and it is a double-glazed insulated unit, and there is moisture build up inside of the window, most likely the original seal has failed.  At this time contact us and we will be more than happy to help you with the replacement of your insulated glass unit.

Over the past few months, BGS Glass has been developing a new website to better serve you, our customers. If you ever have any questions, please feel free to e-mail me at: shannon@bgsglass.com. The staff here at BGS Glass will be happy to take care of all of your glass needs.