W415-1117 / A / 03.11.14
47
IOM
18.2 CALCULATING AIR FLOW
18.3 CONTINUOUS FAN OPERATION
TABLE 8 - CONTINUOUS
FAN CFM
Input
K/Btu/hr
PSC
Motor
HP
Continuous
Fan (CFM)
030-2
1/6
650
040-2
1/6
850
040-3
1/2
900
060-2
1/2
900
060-3
1/2
950
080-3
1/2
1200
080-4
1/2
1250
100-4
3/4
1500
100-5
3/4
1700
120-5
3/4
2000
H12.3.1
H22.2.1
There are circumstances where it may be desirable to know the air
fl
ow delivery through the duct system,
such as when estimating the amount of air
fl
ow available for
air conditioning. This can be done by direct measurement with
electronic or sloped manometers and velometers, or use the
formula in the next column.
H22 2 1
CFM =
Output
1.085 x
∆
T
where:
• CFM is air
fl
ow in cubic feet per minute;
•
∆
T is the temperature rise; and
• O
utput is the furnace output capacity
from the rating plate
.
H22.3.1
When the thermostat continuous fan (G) switch is on without a call for heat or cooling, the indoor fan is
immediately energized. The fan remains energized as long as the call for fan remains without a call for heat or
cooling. This feature allows continuous circulation of air between calls for heating or cooling.
If a callf or heat (W) occurs during continuous fan, the blower will remain energized, the call for heat overrides
the fan.
If a call for cool (Y) occurs simultaneously with the call for fan (G), the call for cool overrides the call for fan.