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Page 37
Setting blower CFM
Note − Turn electrical power off when adjusting mo-
tor pulley. Blower RPM adjustment is accomplished by
changing the motor pulley opening. Loosen Allen screw
and turn pulley clockwise to increase RPM or turn coun-
terclockwise to decrease. Re-tighten Allen screw. (See
Blower motor/drive installation section for the pulley
alignment and belt tensioning method.)
1 − Enter table 13 at design CFM and total external static
pressure. (Design total external static pressure
equals the sum of all pressure drops across all acces-
sories which are installed external to furnace and all
ductwork/accessories. See table 14 for external filter
box with filters pressure drops, C17 coil pressure
drops and EMD17M economizer pressure drops.)
2 − The table yields a value for design BHP and RPM.
3 − Select drive kit so that motor maximum BHP (as
shown in table 15) exceeds the value from table13.
4 − Run the blowers and measure the actual blower shaft
RPM and total external static pressure.
5 − Adjust RPM to the value in table13 which will result in the
design CFM. From design CFM and actual Total Exter-
nal Static Pressure reading, Table 13 gives required
BHP. This value should still be lower than the maximum
BHP delivered by the motor as shown in table 15.
6 − As a final check, measure the motor’s current draw and
compare it to the motor’s nameplate service factor amps
rating (SFA). If the current draw is not less than or equal
to the SFA rating, reduce the motor’s load until it is.
TABLE 13
CFM vs TOTAL EXTERNAL STATIC PRESSURE
Ai
Total External Static Pressure − in. w.g. (Pa)
Air
Volume
f
.10 (25) .20 (50) .30 (75) .40 (100) .50 (125) .60 (150) .70 (175) .80 (200) .90 (225) 1.00 (250) 1.10 (275)
Volume
cfm
(L/s)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
RPM BHP
(kW)
2400
(1135)
- - - - - - - -
535 0.30
(0.22)
600 0.35
(0.26)
665 0.45
(0.34)
720 0.55
(0.41)
755 0.65
(0.48)
825 0.75
(0.56)
875 0.85
(0.63)
920 0.95
(0.71)
965 1.05
(0.78)
2600
(1225)
- - - - - - - -
545 0.35
(0.26)
610 0.40
(0.30)
670 0.50
(0.37)
725 0.60
(0.45)
780 0.70
(0.52)
830 0.80
(0.60)
875 0.90
(0.67)
920 1.00
(0.75)
965 1.10
(0.82)
2800
(1320)
- - - - - - - -
560 0.40
(0.30)
620 0.45
(0.34)
680 0.55
(0.41)
735 1.05
(0.48)
785 0.75
(0.56)
835 0.85
(0.63)
880 0.95
(0.71)
925 1.05
(0.78)
965 1.15
(0.86)
3000
(1415)
- - - - - - - -
570 0.45
(0.34)
630 0.55
(0.41)
690 0.60
(0.45)
740 0.70
(0.52)
790 0.90
(0.60)
840 0.90
(0.67)
865 1.00
(0.75)
930 1.15
(0.86)
970 1.25
(0.93)
3200
(1510)
- - - - - - - -
585 0.50
(0.37)
640 0.85
(0.45)
685 0.70
(0.52)
750 0.80
(0.60)
800 0.90
(0.67)
845 1.00
(0.75)
890 1.10
(0.82)
935 1.20
(0.90)
975 1.35
(1.34)
3400
(1605)
- - - -
535 0.50
(0.37)
595 0.55
(0.41)
655 0.65
(0.48)
710 0.75
(0.56)
760 0.85
(0.63)
805 0.95
(0.71)
855 1.05
(0.78)
895 1.20
(0.90)
940 1.30
(0.97)
- - - -
3600
(1700)
- - - -
550 0.55
(0.41)
610 0.65
(0.48)
665 0.75
(0.56)
720 0.85
(0.63)
770 0.95
(0.71)
815 1.05
(0.78)
860 1.15
(0.86)
905 1.25
(0.93)
945 1.40
(1.04)
- - - -
3800
(1795)
- - - -
570 0.60
(0.45)
625 0.70
(0.52)
680 0.80
(0.60)
730 0.90
(0.67)
780 1.05
(0.78)
825 1.15
(0.86)
870 1.25
(0.93)
910 1.35
(1.01)
955 1.50
(1.12)
- - - -
4000
(1890)
- - - -
585 0.70
(0.52)
645 0.80
(0.60)
695 0.90
(0.67)
745 1.00
(0.75)
790 1.10
(0.82)
835 1.25
(0.93)
880 1.35
(1.01)
920 1.45
(1.08)
960 1.60
(1.19)
- - - -
4200
(1980)
550 0.70
(0.52)
605 0.80
(0.60)
660 0.90
(0.67)
710 1.00
(0.75)
760 1.10
(0.82)
805 1.25
(0.93)
850 1.35
(1.01)
890 1.45
(1.08)
930 1.60
(1.19)
970 1.70
(1.27)
- - - -
4400
(2075)
570 0.80
(0.60)
625 0.90
(0.67)
675 1.00
(0.75)
725 1.10
(0.82)
770 1.20
(0.90)
815 1.35
(1.01)
860 1.45
(1.08)
900 1.60
(1.19)
940 1.70
(1.27)
- - - - - - - -
4600
(2170)
590 0.90
(0.67)
645 1.00
(0.75)
695 1.10
(0.82)
740 1.25
(0.93)
785 1.35
(1.01)
830 1.45
(1.08)
870 1.60
(1.19)
915 1.75
(1.31)
950 1.85
(1.38)
- - - - - - - -
4800
(2265)
610 1.00
(0.75)
660 1.10
(0.82)
710 1.25
(0.93)
755 1.35
(1.01)
800 1.45
(1.08)
845 1.60
(1.19)
885 1.75
(1.31)
925 1.85
(1.38)
965 2.00
(1.49)
- - - - - - - -
5000
(2360)
630 1.10
(0.82)
680 1.25
(0.93)
730 1.35
(1.01)
775 1.50
(1.12)
815 1.60
(1.19)
860 1.75
(1.31)
900 1.90
(1.42)
940 2.00
(1.49)
975 2.15
(1.60)
- - - - - - - -
NOTE − All air data is measured external to furnace using rear return air opening without air filters in place.
Bold text indicates 2 H.P. (1.5 kW) drive kits.