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Rev 2.0
63-7048 1998 Honeywell Inc.
Page 2 of 22
Automatic Humidity Control
The Honeywell H1008 Automatic Humidity Control with HumidiCalc+
Software
is the world’s most advanced stand-alone humidity control. Simple to install, easy to
troubleshoot, it is designed to save the installing contractor time, while maximizing
benefits to the homeowner. It’s much more than a humidistat - it’s a sophisticated
electronic control with the ability to maintain a comfortable humidity level in a home,
while preventing condensation on windows over a wide range of weather conditions.
Back to Basics - Expressing Humidity
When most people think of humidity they probably are thinking of “relative humidity.”
But there is a significant drawback in expressing humidity in terms of relative humidity.
In order for relative humidity to be meaningful, the temperature of the air needs to be also
known. Simply stating that the “humidity is X %” does not really indicate how much
moisture is present in the air. The best measure of the humidity level in the air is
dewpoint, not relative humidity. Dewpoint is a measure of the absolute amount of
moisture in the air. If the temperature of the air is raised or lowered the dewpoint will
remain constant, unless moisture is added or taken away. Figure 1 shows the effect that
changing temperature has on relative humidity. With conditions of constant moisture
content in the air (dewpoint of 50
F) the relative humidity varies between 35% and 70%
as the temperature varies between 60
F and 80
F.
Figure 1 – Variation of Relative Humidity with Changes in Temperature at a
Constant Moisture Level
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
55 60 65 70 75 80 85
Dry Bulb Temperature - deg F
Relative Humidity - % RH