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High Relative Humidity Levels and Window CondensationWhat is relative humidity?Source: Merriam-Webster's Medical Dictionary, 2002 Merriam-Webster, Inc.

Relative humidity: n: the ratio of the amount of water in the air at a give temperature to the maximum amount itcould hold at that temperature; expressed as a percentage.

Still don't understand, well lets look at it in a different way. When air reaches 100% relative humidity level theair is said to be saturated. This means the air cannot hold any more vapor, and that the vapor will turns to liquid.

In nature, it means rain. In your home, we have condensation. Warmer air holds more vapor than cooler air.When the air temperature increases, the amount of relative humidity decreases. How does this affect your

home? Simple, when your home is heated, the air is drier and the lower the chance of condensation forming.What drier does is lower the dew point.

So, what's dew point? Dew point is the temperature that water vapor in the air becomes saturated andcondensation begins.

Here an example of how temperature and relative humidity factors in with condensation and windows:If you keep the inside temperature of your home at 70o F, the current outside temperature is a frigid 0oF, and

the relative humidity inside your home is 35%, then the dew point inside your home will be 41oF. Let say thatyour home has regular double pane glass, with no low-e coating or insulative gas fill, then the insidetemperature of your window surface will be 43o F. Because the temperature of your windows is higher than the

dew point, condensation does not form on your windows. However, if you keep the inside temperature lower,then the relative humidity of your home would increase. Dropping the temperature of your home to 66o F

would increase the humidity to 45%, making the dew point 44oF. Now, the temperature of the glass is lowerthan the dew point, and condensation forms on the windows.

If the conditions inside your home seem to encourage condensation, simple increase the air temperature slightlyand this will prevent condensation from forming.

The same effect is also in reverse. By lowering the inside air temperature, the temperature of the glass surfacefells below the dew point, causing condensation to form on the window.

Condensation Can Be Caused by Lack of Air Movement.

Without air movement, evaporation is almost impossible. Think of a hot, humid summer day when there isn't a

gently breeze. Now, take that same day and add a gently breeze. The thermometer may read the same, butbecause of the airflow, it doesn't seem as hot. Why, because of evaporation. Evaporation occurs when there is

an increased disturbance between water and air. After a heavy rain, it may take two or three days for a puddle ofwater to evaporate. However, if that same puddle is spread out, it can evaporate in a matter of hours. The more

surface area of the water is exposed to air currents, the faster evaporation occurs. When you take a shower anddo not turn on the exhaust fan, your mirror clouds over with condensation.

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However, if you turn on the exhaust fan, the amount of condensation is less. So, what does evaporation have todo with windows?

Condensation occurs on a surface because when there is a lack of air current no energy is provided for water torevert in vapor. A strange thing sometimes occurs when replacing old windows with new, energy efficient

windows, more condensation occurs. Why? You've just invested a lot of money and your windows havecondensation. This can be a good thing. How, you ask. With your old windows, the inside of your home had

favorable conditions for condensation, but because your old windows permitted draft to occur, the constant

airflow evaporated any condensation. However, your drafty windows also increased your heating bill. Your newenergy efficient windows don't permit heat to escape, so the moisture in the air settles condenses on yourwindows as condensation. Your energy efficient home has less heat loss and a better balance of inside humidity

and temperature.

How do you stop condensation on your windows?

The condensation on your windows comes from an interaction of temperature, humidity, and a lack of airmovement. You must isolate each factors and analyze them to properly establish the source, and eventual the

solution the condensation on your windows.If replacing windows, invest in Low-E and inert gas fill technology. These windows keep the glass surface

temperatures higher, reducing the chances of condensation.Keep the humidity levels indoor between 30-50%. If the indoor humidity level is above 50% there is a strongerprobability of condensation forming on your windows, even if they are a low-e insulated product.

Keep sufficient air circulation in your home.

This can be accomplished by:

o Vent clothes dryers, gas burners, etc. to the outdoors.o Insure all ventilation equipment is properly adjusted.o Use exhaust fans in your kitchen and bathroom. By simply opening a window, and airing out

your kitchen, bath, and laundry rooms a few minutes will help to reduce condensation.

o Inspect your attic louvers to ensure they remain open year around, also make sure there isproperly ventilation in your crawl spaces. If you are not sure there is adequate ventilation,

consult with a local heating and ventilating contractor.

Condensation can be controlled. Vinyl replacement windows will help to eliminate the cold window surfaces

that create a desirable environment for condensation.

Finally, you must establish an environment, which balances healthy living conditions with energy efficient

properties for your home.