EFCO Special Purpose Windows Understanding Condensation - Manual

General Service and Maintenance Manual
SECTION 5
CONDENSATION
5.a. ABOUT CONDENSATION:
Moisture on windows and doors is commonly referred to as condensation. While it can be concerning or frustrating, con-
densation can be minimized or prevented by controlling the inside relative humidity.
Interior Condensation:
Condensation on the interior of windows and doors is not caused by the window or door product. Condensation is the
result of high humidity levels in the building. Air with high humidity holds water vapor until it comes into contact with a
surface temperature less than or equal to the dew point (the temperature at which air becomes saturated and produces
dew). Because window surfaces are usually the coldest part of the building envelope, condensation appears on win-
dows first, generally in the form of water droplets of frost on the roomside of the window. As interior air becomes drier or
as the window surfaces become warmer, condensation will begin to dissipate.
Replacing drafty windows and doors reduces air infiltration into the building, making it tighter. Because a tighter building
retains more humidity, condensation on colder surfaces in the building may occur more frequently than before the reno-
vation.
EFCO CORPORATION 2013 PAGE 13
Condensation Causing Conditions Condensation Preventing Conditions
Interior Exterior
Temp: 70 ࡈ F
Humidity: 30%
Dew Point: 37
ࡈ F
Temp of
Int. Surface
of Window: 43
ࡈ F
Exterior Air
Temp: 0
ࡈ F
x Humidity is at recommended level.
x Lower humidity causes lower dew point.
x No condensation appears on interior of window because
temperature is above due point.
Interior Exterior
Temp: 70 ࡈ F
Humidity: 40%
Dew Point: 44
ࡈ F
Temp of
Int. Surface
of Window: 43
ࡈ F
Exterior Air
Temp: 0! F
x Humidity is higher than recommended.
x High humidity causes higher dew point.
x Condensation appears on interior of window because
temperature is below due point.
Maximum Recommended humidity Levels
Outside Temperature Inside Humidity
20
ࡈ F to 40ࡈ F
Not over 40%
10
ࡈ F to 20ࡈ F
Not over 35%
0
ࡈ F to 10ࡈ F
Not over 30%
-10
ࡈ F to 0ࡈ F
Not over 25%
-20
ࡈ F to -10ࡈ F
Not over 20%
-20
ࡈ F or below
Not over 15%