Where does condensation come from?
Today’s energy-efficient homes are built more airtight than ever. But in addition to sealing in warmth and air conditioning, they also tend to hold in too much moisture-laden air.

If your home contains excessive moisture and it’s cold outside, the first place you’ll see it is on your windows. You may think this means there’s a problem with your windows, but it doesn’t. In fact, the vast majority of window condensation problems are not the result of faulty windows. The windows are just indicating that your home needs added ventilation to lower the amount of moisture in the air.

What is humidity?
Humidity, water vapor, moisture, and steam are all the same in that they are each a form of water. Humidity is an invisible gas. It is present in varying quantities in nearly all air. This moisture in wet air tries to flow toward drier air and mix with it.

Scientists describe this force as "vapor pressure." It is often a very powerful force indeed. It can act independently of the flow of the air which holds the moisture. Vapor pressure can force moisture easily through wood, plaster, brick, and cement—right through most of the materials we use to build our homes. That is exactly what happens when moisture seeks to escape from the humid air usually found inside your home to the drier winter air outside.
 

Can condensation damage your windows?
Occasional beads of moisture on the glass of your windows usually isn’t a problem.

For example, it’s likely your bathroom mirror and windows will steam up after a hot shower. Or your kitchen window may fog up when you’re boiling food on the stove. But in both these cases, the moisture clears in a matter of minutes. However, if your windows are “sweating” at other times - or stay that way for any length of time - you probably do have a problem.

• Wood frames and sash can warp and become difficult to operate.
• Paint can peel and other finishes become mottled or stained.
• Insulation can become damp, damaging ceilings and walls.
• Exterior siding and finishes can become blistered and warped.
• Interior surfaces can become breeding grounds for mold and mildew.

This is why it’s so important to take steps to control and eliminate excess moisture.

Where does all the moisture come from?
 In a word, everywhere.

• In the kitchen, moisture is generated by cooking food, using the sink, running the dishwasher.
• In the bathroom, from showers, hot tubs and spas.
• Washers and indoor-vented dryers contribute as well.
• Basements and crawl spaces can channel dampness from the ground into your home
• Even breathing and perspiration add moisture to indoor air.

More moisture trapped in less space
First, more washing, more bathing, more showers, more appliances, and more gas furnaces all pour more water vapor into homes than in former years. 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 to 8 lbs. per day, dishwashing 1.2 lbs., etc.

All of this moisture must eventually escape from your home. So you 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 houses with no basements have further moisture problems.

How to reduce humidity
If you test humidity in your home, be sure to use an accurate instrument, preferably a good sling psychrometer. Remember, too, that these relative humidity’s are for 70 degrees F. For higher temperatures, lower humidity’s are required.

3. Practical steps to control condensation
Here, arranged from easy to more difficult, are the steps you should take to reduce condensation on your windows.

1. Shut off furnace humidifier and any other humidifying devices in your home.
2. Open fireplace damper to allow easier escape for moisture.
3. If Troublesome condensation persists see your heating contractor about an outside air intake for your furnace; about venting of gas-burning heaters and appliances; or about installation of ventilating fans.

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.

But in practice, window condensation and reducing humidity may become very complicated because a score or more of entirely different conditions may affect the way the condensation problem works out in different homes. Let us just mention a few:

• The number and types of windows in the home.
• The type of double glazing system on the windows.
• The heating system—hot air or water—perimeter or interior wall heating.
• The type of insulation and vapor barrier.
• Foam-Insulated Pionite™ Seat boards.
• Even the type of soil and quality of drainage
.

What else can you do to lower excessive indoor moisture levels?
The basic principle of reducing window condensation is simple. When there’s too much condensation on your windows it means the humidity is too high in your home for the current condition outside. Here are some additional actions that may help reduce excessive humidity levels:

• Open your windows occasionally to vent excess moisture.
• If the condensation is on the storm window, open it periodically to vent excess moisture.
• Open drapes and blinds to allow warm house air to circulate against the window.
• Turn off your furnace humidifier or other home humidifiers.
• Make sure dehumidifiers are working properly and well drained.
• Be sure that louvers in the attic or basement crawl space are open and are of adequate size.
• Run ventilating fans in the kitchen and bathrooms more often.
• Air out your house by opening a door or window for a few minutes after the bathroom, kitchen or laundry has steamed up.
  

Better Business Bureau—Telltips #421: Condensation on Windows
Condensation is visible evidence of excessive moisture in the air. It may appear as water, frost, or ice on the room surface of windows and doors. The warmer the air, the more water it can hold. This means that the air in the center of any given room will hold more water than the air adjacent to the window or door walls, since this area is always colder. When the warm moisture-laden air moves toward the cooler window or door wall, it becomes cooler and could not hold the moisture it held when it was warmer. Therefore, the moisture is dropped and appears as water on the glass and frames of windows and doors. This occurs more frequently during the winter months, because of the extreme difference between the inside and outside temperatures. If you wish to avoid condensation during the winter months, when the average outdoor temperature drops to 35 degrees or less, it would be wise to maintain a 25 to 35 degree relative indoor humidity.

Ventilation is a very effective way to remove excessive moisture from the air, which is why old poorly insulated houses with single glazed windows often times do not have condensation problems. This is because the air is changed by infiltration around the windows, vents, and other openings. Newer homes which are constructed to meet current insulation standards and energy conservation requirements; or older homes which have been newly insulated through the addition of added attic or basement insulation and installation of prime windows with dual or triple glazed glass, are now so air tight that they present a new problem.

If you have an existing moisture or condensation problem, do not count on correcting it merely by installing new windows. Windows do not cause condensation; therefore, windows cannot cure condensation. However, an energy efficient vinyl replacement window with Super Spacer warm edge technology, Argon gas, and Low E glass helps to greatly reduce condensation. Request a free vinyl replacement window estimate.