Aprilaire 448 - Manual (Page 6)

Your Aprilaire Automatic Humidifier, is a high precision system
that will accurately maintain the relative humidity in your home.
For every 1º change in outdoor temperature, the control will
automatically adjust the indoor relative humidity (RH) by
1 /
2
%.
If you would like to determine the RH in your home, follow
these steps:
1. Determine the outdoor temperature.
2. Activate the furnace blower by setting your thermostat fan
switch to the “On” position, or setting your thermostat to a
higher temperature.
3. Turn the control dial setting to the “Off” position. Then, slowly
turn the dial clockwise until you hear the solenoid valve “click
on.” Next, slowly turn the dial counter clockwise until you hear
the solenoid valve “click off.” At this point, make note of the
dial setting.
4. Locate your dial setting on Table 2. Follow the dial setting to
the right until it intersects with the current outdoor
temperature. This is the relative humidity in your home under
existing conditions.
5. Return the thermostat and the control to their original settings.
The Automatic Humidifier will accurately control the humidity in
your home to a maximum of 45% RH and a minimum of 10% RH.
The values of outdoor temperature and dial settings may fall in
between or outside of the listed values in Table 2. In these cases,
you can only approximate your home’s actual indoor RH.
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Off
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1
Te
st N
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A
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Automatic Mode
(Figure A) The relative humidity in
your home will now be
accurately controlled to
meet your needs and should
not need further adjustment
during future heating
seasons. Make note of the
dial setting in the event you
temporarily move the knob
when performing annual
maintenance of the Aprilaire
Humidifier