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High Relative Humidity
Levels And Window Condensation
What 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 it could 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 the air 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 and condensation 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 that your home has regular double pane glass, with no low-e coating
or insulative gas fill, then the inside temperature 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 lower than the dew point, and condensation
forms on the windows.
No Condensation Condensation Outside Temperature 0oF 0oF
Inside Temperature 70o F 66oF Glass Surface 43oF 42oF Relative
Humidity 35% 45% Dew Point Temp. 41oF 44oF
If the conditions inside your home seem to encourage condensation,
simple increase the air temperature slightly and this will prevent
condensation from forming.
The same effect is also in reverse. By lowering the inside air
temperature, the temperature of the glass surface fells below the dew
point, causing condensation to form on the window.
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