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Roof Downblast - Exhaust
Belt Drive
GB-300
Performance certified is for installation type A: Free inlet, Free outlet. Power rating (BHP) does not include transmission losses. Performance ratings include the effects
of a birdscreen. The sound ratings shown are loudness values in hemispherical sones at 5 ft. (1.5 m) in a hemispherical free field calculated per AMCA Standard 301.
Values shown are for installation type A: free inlet hemispherical sone levels.
Performance certified is for installation type A: Free inlet, Free outlet. Power rating (BHP) does not include transmission losses. Performance ratings include the effects
of a birdscreen. The sound ratings shown are loudness values in hemispherical sones at 5 ft. (1.5 m) in a hemispherical free field calculated per AMCA Standard 301.
Values shown are for installation type A: free inlet hemispherical sone levels.
1
3
⁄4 (44)
Damper Size = 30 x 30 (762 x 762)
Roof Opening = 32 x 32 (826 x 826)
Shroud Thickness = 0.064 (1.6)
Motor Cover Thickness = 0.051 (1.3)
Curb Cap Thickness = 0.064 (1.6)
^Approximate Unit Weight = 320 lbs. (145 kg)
All dimensions in inches (millimeters). *May be greater depending on
motor. ^Weight shown is largest cataloged Open Drip-Proof motor.
D
O
N
O
T
S
E
L
E
C
T
T
O
T
H
E
L
E
F
T
O
F
T
H
I
S
S
Y
S
T
E
M
C
U
R
V
E
Static Pressure (in. wg)
Static Pressure (Pa)
Volume (cfm x 1000)
3
Volume (m /hr x 1000)
RPM (Belt)
HP
Density 0.075 lb/ft
3
Density 1.2 kg/m
3
50
(1270)
8
1
⁄4 (210)
*36
(914)
40
(1016)
Motor
HP
Fan
RPM
Static Pressure in Inches wg
0 0.125 0.25 0.5 0.75 1 1.25 1.5 1.75 2
300
1/3
300
CFM
4859 3976
BHP
0.18 0.19
Sones
9.3 5.3
365
CFM
5912 5222 4340
BHP
0.33 0.35 0.35
Sones
9.2 6.2 5.7
1/2 420
CFM
6803 6222 5537
BHP
0.50 0.52 0.53
Sones
9.6 8.0 7.0
3/4 475
CFM
7694 7197 6616 5095
BHP
0.72 0.75 0.77 0.74
Sones
11.4 10.6 9.6 8.1
1 530
CFM
8585 8150 7640 6456 4195
BHP
1.00 1.04 1.06 1.07 0.91
Sones
13.4 12.9 12.2 10.7 9.4
1
1
⁄2 600
CFM
9719 9334 8907 7952 6721
BHP
1.45 1.49 1.53 1.55 1.52
Sones
15.9 15.4 14.9 13.8 12.2
2 665
CFM
10772 10425 10060 9228 8269 7025
BHP
1.97 2.02 2.06 2.11 2.11 2.03
Sones
18.8 18.2 17.7 16.8 15.7 13.7
3
713
CFM
11549 11226 10901 10129 9297 8283 6691
BHP
2.43 2.48 2.53 2.59 2.61 2.57 2.38
Sones
21 20 19.6 18.9 18.0 16.4 13.7
760
CFM
12311 12007 11704 10997 10242 9369 8293 6437
BHP
2.94 3.00 3.05 3.13 3.16 3.15 3.06 2.76
Sones
23 22 21 21 19.8 18.6 16.8 14.0
5
825
CFM
13363 13084 12804 12175 11501 10770 9909 8885 7128
BHP
3.76 3.82 3.88 3.97 4.02 4.05 4.01 3.90 3.56
Sones
25 25 24 24 23 22 20 18.7 16.1
890
CFM
14416 14157 13898 13335 12716 12073 11379 10536 9568 7963
BHP
4.73 4.79 4.85 4.96 5.03 5.06 5.09 5.02 4.89 4.54
Sones
28 28 28 27 26 25 24 22 21 18.7
MAXIMUM BHP AT A GIVEN RPM = (RPM/517)
3
MAXIMUM RPM = 890
TIP SPEED (ft/min) = RPM x 7.985
MAXIMUM MOTOR FRAME SIZE = 184T