1. science
2. weather

What is Condensation?
The moisture that appears on the window
surface as water when temperatures are
above freezing, and as frost when
temperatures are below freezing, is termed
condensation. Condensation occurs when
the temperature of any surface falls below
the dew point. The dew point constantly
changes with the air temperature and relative
humidity. At any given temperature there is
a maximum amount of water vapor the air
can hold. When the air can no longer hold
the moisture, it will deposit that moisture on
any surface that falls below the temperature
at the saturation pressure, or dew point.
Windows are the Yardstick.
The concern for condensation on windows is
common during the time of the year when
conditions are reaching their
extremes.
It
is
often
overlooked that condensation
might occur on other building
substrates as well. Windows
do not cause condensation,
but indicate when conditions
are favorable for condensation to form.
Condensation is a result of temperature and
humidity. Water is in our atmosphere and
will condense on colder surfaces when
conditions are favorable.
Condensation is Undesirable.
While higher humidity levels are sometimes
considered more comfortable, they are not
desirable for other
reasons. High humidity
levels
can
cause
condensation to form on
windows and doors. In
addition, high humidity
can increase the chance of water vapor
condensing in wall and ceiling insulation,
deteriorating wood framing, sheathing, and painted
surfaces. While some level of condensation is
acceptable, humidity levels must be moderated and
controlled.
How is Condensation Controlled?
There are three main variables to consider when
trying to control condensation: 1) the exterior
temperature, 2) the interior temperature, and 3) the
inside relative humidity. The inside temperature
and the interior humidity are the things we have
control over.
Managing Condensation.
EFCO Corporation is a material supplier for
fenestration products. We recommend
that building design incorporate humidity
control. Whether it is new construction
or renovation, condensation will occur
because water is in the atmosphere.
Things to consider include the reduction in the
humidity level and increasing air circulation around
problem areas. Window coverings restrict air
movement around the window which can increase
the formation of condensation.
If window
coverings must be used, keep them open as much as
possible. If the window is recessed in a wall cavity,
natural air flow may not be adequate to minimize
condensation, therefore a fan may be necessary to
assist the air circulation.
Ceiling fans can be
installed to assist air flow and dehumidifiers can be
used as a means of reducing humidity. If the
humidity level is controlled, condensation can be
managed.
When Does Temporary Condensation Occur?
There are some situations where condensation
occurs that is temporary. New construction and
remodeling will increase the
probability of
condensation because wood, drywall, cement and
other building materials take time to cure and dry
out, thus increasing moisture and humidity.
During the summer, building materials
absorb moisture. At
the beginning of the
heating
season,
temporary
condensation
can
occur until the
building loses the excess moisture it gains
during summer months.
Sharp drops in
temperature can also create temporary
condensation problems during the heating
season due to the trapped warmer humid air
inside the building. Cracking a window for
a short time can help clear up condensation.
The interior temperature and the interior
relative humidity are the basic variables
used to control condensation.
Product Selection.
Selecting the proper fenestration product for
the geographic location, and having an
understanding of the causes of condensation
will make a significant difference in the success of
minimizing condensation. Metal and glass surfaces
have higher conductivity rates and will dissipate
heat quicker than wood, cloth and other interior
surfaces. Given the same relative humidity in the
room, condensation will occur at window surfaces
more often.
Is There a Way to Select a Window for my
Geographic Location?
Fenestration products are usually tested to
determine a Condensation Resistance Factor (CRF).
The CRF is a rating obtained by
standardized
testing
which
establishes a prediction, within
reasonable accuracy, of the
formation of condensation of a
fenestration product.
EFCO
Corporation publishes the CRF
ratings of standard products.
These CRF ratings can be obtained from the product
overviews in EFCO Corporation’s product
literature, or visit www.efcocorp.com.
Identify your Outside Design Temperature:
Identify Maximum Recommended Humidity Levels:
TABLE B
MAXIMUM RECOMMENDED HUMIDITY LEVELS
Based on engineering studies at 70°F conducted at the University of Minnesota Laboratories.
OUTSIDE AIR TEMPERATURE
INSIDE RELATIVE HUMIDITY
-20 Degrees F. or Below
Not Over 15 Percent
-20 Degrees F. to -10
Not Over 20 Percent
-10 Degrees F. to
0
Not Over 25 Percent
0 Degrees F. to 10
Not Over 30 Percent
10 Degrees F. to 20
Not Over 35 Percent
20 Degrees F. to 40
Not Over 40 Percent
Relative humidity levels above these are not recommended at the low outside temperatures
indicated, unless special provisions are taken in building construction.
If higher relative humidity levels are required because of special interior environmental
conditions, the product manufacturer should be consulted.
Select the Recommended CRF for the product:
TABLE A
MINIMUM RECOMMENDED CONDENSATION RESISTANCE FACTORS (CRF)*
Inside
Relative
Humidity
15%
20%
25%
30%
35%
40%
-20°F
46
52
57
60
-
-
-10°F
39
46
52
56
60
-
0°F
30
39
45
52
57
61
+10°F
17
29
37
44
50
57
+20°F
0
16
25
34
40
48
Outside
Temperature
*Specifications of above Resistance Factors are based upon an inside air temperature of 68°F and outside
window velocity of 15 MPH.
Select EFCO Corporation’s Product:
Maximum Recommended Indoor Humidity at 70º Indoor Temperature
EFCO®
2700
2700
Product
510 I
2900
810 I
Project
Outside
CSMT
Out
Temperature
890
1325
Tilt
Turn
-20°F
19%
15%
23%
21%
25%
17%
27%
-10°F
23%
19%
27%
26%
30%
21%
32%
0°F
28%
23%
33%
31%
35%
26%
37%
+10°F
34%
30%
36%
37%
41%
32%
43%
+20°F
42%
37%
46%
44%
47%
40%
50%
3450
Single
Hung
660
Single
Hung
690
Double
Hung
6600
3500
Slider
6555
Slider
3900
-20°F
22%
16%
13%
36%
22%
25%
29%
-10°F
27%
20%
17%
40%
27%
30%
33%
0°F
32%
25%
22%
45%
32%
35%
38%
+10°F
38%
31%
28%
50%
38%
41%
44%
+20°F
44%
38%
36%
57%
44%
47%
51%
3000
Sliding
Door
3015
Sliding
Door
T35I
403
Storefront
960
5600
5900
-20°F
17%
18%
19%
24%
25%
33%
21%
-10°F
21%
22%
24%
29%
30%
37%
26%
0°F
25%
27%
30%
34%
35%
41%
31%
+10°F
31%
33%
36%
40%
41%
48%
37%
+20°F
38%
40%
43%
46%
47%
55%
44%
EFCO®
Product
Outside
Temperature
EFCO®
Product
Outside
Temperature
Recommendations are for design purposes only, actual building conditions will vary.
This is a brief review of condensation and how it can be managed. Selecting the proper
fenestration product from EFCO Corporation and designing the building with proper
climate control will help manage condenstion.
Information Sources:
AAMA Window Selection Guide 1988, AAMA 101 /IS2-97
1999 ASHRAE Handbook HVAC Applications
AAMA 1502.7, AAMA 1503.1,AAMA 1503.98
The Condensation Answer Book. Andersen
Miscellaneous EFCO Corporation Historical Data.