Automatic Humidifiers Owner's Manual

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Manual Mode: (Automatic Mode – see pg 4)
Your Aprilaire Humidifier Control is installed in the cold air return. It is
important to anticipate a drop in outdoor temperature and reduce the setting
accordingly to avoid excessive condensation. For example, with an outdoor
temperature of 20° the correct setting will be 35% relative humidity. If the
temperature is expected to fall to 0° that evening, then merely reduce the
setting to 25% several hours prior to the temperature change.
The recommended settings on the Humidifier Control are based on years
of research and experience (see Table 3). These settings represent a
compromise between RH levels that would be most desirable for comfort
reasons and humidity levels that are suitable for protection of your home
and to avoid condensation on your windows. For example, a wintertime
indoor RH of 50% may be considered ideal, but unfortunately, it probably
would result in damage to your home. Observance of the recommended
RH levels on your Humidifier Control, therefore, is an important safeguard.
Condensation of water on inside windows in the form of fogging or frost
is usually an indication of too much relative humidity. This same
condensation can take place in other areas in your home with the
possibility of damage resulting.
As an example, if the outdoor temperature is 20°F, and, following step 3,
the humidifier turns off at “5” on the dial range, then the RH in your home is 35%.
-10 0 10 20 30 40
1 10 10 10 15 20 25
2 10 10 15 20 25 30
3 10 15 20 25 30 35
4 15 20 25 30 35 40
5 20 25 30
35 40 45
6 25 30 35 40 45 45
7 30 35 40 45 45 45
Outdoor Temperature (°F)
Dial Setting
TABLE 2 – % Relative Humidity Guide