Aprilaire 448 - Manual (Page 8)

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To check the humidifier operation, set the knob to “test”, make
sure that the water saddle valve is open and that there is electricity
to the unit. Generally, the furnace blower motor must be operating
for the Aprilaire Humidifier to function. After the humidifier has oper-
ated for one minute and water is entering the unit and coming out at
the drain, reduce the humidistat setting to the recommended inside
relative humidity, depending on the outside temperature. DO NOT
LEAVE IN TEST MODE AS HUMIDIFIER WILL NOT OPERATE. Follow the
suggested settings prior to a drop in the outside temperature.
MANUAL MODE
(Figure B) The humidistat is a precision
instrument that can be used
to determine the RH accurately in
your home during the winter. Turn
the dial to the lower setting, then
reverse the dial direction slowly
until you hear the solenoid valve
“click on”. At this point, read the
RH on the dial. This will be very
close to the actual RH in your
home. (See Figure B)
Outside Temperature Recommended RH
+40° 45%
+30° 40%
+20° 35%
+10° 30%
0° 25%
–10° 20%
–20° 15%
(Table 3) Outdoor-Indoor Relative Humidity