Understanding Condensation

Gilkey Window Company understands your concerns about the interior or exterior condensation appearing on your windows. In order to help you this document explains the phenomenon and ways to reduce or eliminate excess moisture in your home.

However, if you see condensation between the panes of glass on your windows this would indicate a seal failure and the unit will need to be replaced. Please contact our service department for replacement:

In Cincinnati, Dayton or Louisville call 513-587-6262 or 877-591-2200.

In Chicago call 708-459-8905 or 866-584-7226.

We hope this document provides enough information for you to solve your interior/exterior condensation problem. If we can be of further assistance please do not hesitate to call on us.

Condensation on windows and other cool surfaces in the home can be both annoying and possibly cause damage to your home. Because the most often visible condensation is seen on windows, it is easy to blame condensation as being a window fault. This is not true in most cases. Windows do not manufacture water. Any cool surface will cause excess humidity to condense on it. If there is condensation on windows, you may be assured there is condensation on walls. This is more serious since that can penetrate the walls and cause internal problems.

The cause of condensation is air saturated with too much humidity or water. When this happens, air cannot hold the excess humidity. It gets rid of it by condensing it on the most convenient cool surface.

• Normal breathing and perspiration by a family of four adds a half pint of water to the air each hour.
• Cooking can add up to four or five pints of water per day.
• A shower can add another half pint.
• Dishwashers, washing machines, and dryers can add several pints of water to the air.
• Humidifiers which are adding too much humidity.
• Poorly insulated crawl spaces which allow humidity to invade the home.
• New homes will often emit excess humidity for the normal drying out of the building products. This is normal and will usually adjust itself within a year or less.

In other words, if condensation is to be reduced, the source and amount of humidity in the air needs to be determined.

Warmer air holds more moisture than cool or cold air. This is illustrated on a humid, hot summer day when condensation appeared on a cold glass. This means that the amount of moisture in the air has reached its maximum and can't hold any more. Therefore, it gets rid of it by condensing it on the nearest cool or cold surface.

As air cools, it can't hold as much moisture and therefore, condensation will appear more quickly.

So what is the ideal amount of relative humidity in the air? Based on keeping an indoor temperature of 70° F, it will vary with the outdoor temperature. But as a guide, the following relationship should help.

If your relative humidity is above these levels, you probably will have condensation on any cool surface.

In some cases this may be true. In older houses, the insulation and weather-stripping and other house tightening factors allowed the house to breathe and exchange drier air with inside more humid air.

Of course, windows also were not so air tight and caused colder air to enter the house and can also cause the surface of the window to be colder. Today, because we are all energy conscious, houses, doors and windows are far more energy efficient. This makes us all more comfortable, but may trap humid air inside the home.

The obvious answer is to reduce the humidity and decrease the number of cool surfaces in your home.

Your first step is to find what the humidity level in your home is. This will need to be monitored regularly as the temperature outside varies. Devices which measure humidity are called hygrometers. They can be purchased at most reliable hardware and home center stores.

• Make sure your humidifier is working correctly; turn it down as the weather becomes colder.
• Vent all appliances and exhaust fans to the outside.
• Vent attic and crawl spaces.
• Cover the earth in your crawl space with a vapor barrier.
• Run exhaust fans while cooking or bathing.
• If you have a forced air furnace, make sure your home is properly ventilated by installing a fresh intake.
• Don't store firewood inside.
• As a temporary solution, you may want to try opening your windows a little each day to allow the exchange of colder, drier air with warmer more humid air. This should not affect your energy bill in any substantial manner.
• Open your drapes during the day.

If these common remedies don't work, the condensation problem should be looked at by a heating contractor. 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 than a major painting job or plaster work caused by excess water vapor.

Windows, doors, and skylights have become an important part of the energy saving plan. They do not allow cold air to enter around a window, thus cooling the surface. Spacers between glazing in double or triple glazed windows are more energy efficient and do not allow cold air to migrate through them causing the glazing to cool.

Special metallic coatings have been developed (known as Low E or low emissivity) which reflects radiant heat and restricts its flow through glass. During cold weather, it will keep heat inside. In hot weather, it keeps heat outside.

Using energy efficient windows will keep the interior glass surfaces warmer and thus reduce the interior cool surfaces on which moisture can condense.

In order to reduce condensation:

• Reduce the amount of moisture in the air as the outside temperature gets colder (see chart page 1).
• Make sure your home is properly ventilated.
• Use exhaust fans.
• Use vapor barriers on the earth in your crawl space.
• Use a hygrometer to measure and regulate your humidity level.
• Use energy efficient windows. (Installing a storm window in an older home may help.)
• If building a new home, make sure your builder is using only kiln dried lumber and make sure he places heat vents beneath patio doors.

Remember, there is always a possibility that in very cold, unusual circumstances, you may still have some temporary condensation. But if the humidity level is proper and the home correctly vented, this will be short lived.

Exterior condensation is a form of dew that occurs on windows primarily in the morning when days are warm and humid, but nights are cool. The glass simply provides a surface on which the moisture condenses visibly. Typically, it clears as the day warms. So the only recourse is to wait for Mother Nature and when the sun rises, the dew point drops, or the winds pick up, then condensation will evaporate. Exterior condensation can occur at any time, especially in warm, humid climates where interior temperatures are cooler than outdoor conditions. Exterior condensation means that windows are doing their job properly.

While an inconvenience, exterior condensation should not concern you and will not affect the interior of your home. Since you cannot control the relative humidity outside your home, the only step you can take to combat exterior condensation is to warm the inside surface of the window, as this is a way to warm the outside surface. Draperies should be open to allow as much heat transfer through the glass as possible. Shrubbery immediately adjacent to the glass can increase the local humidity and may need to be moved. Seeing exterior condensation on those rare days should be reassurance that your windows are doing their job, keeping your heating and cooling in your home where it belongs and saving you money.