4
Centrifugal Single-Width Blower
®
Ducted Outlet Installations
Discharge Duct Turns
- Duct turns located near the
fan discharge should always be in the direction of the
fan rotation.
Fan performance is reduced when duct turns are
made immediately off the fan discharge.
To achieve cataloged fan performance
there should be at least
three equivalent
duct diameters of
straight ductwork
between the fan
discharge and
any duct turns.
Rotat
io
n
R
ot
ati
on
R
ot
ati
on
Rotat
io
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
Three fan wheel diameters
One fan
wheel
diameter
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
ATIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
Non-Ducted Installations
Inlet Clearance
- Installation of a fan with an open
inlet too close to a wall or bulkhead will cause reduced
fan performance. It is desirable to have a minimum of
three-fourths of a wheel diameter between the fan inlet
and the wall.
Free Discharge
- Free or abrupt discharge into a
plenum results in a reduction in fan performance. The
effect of discharge static regain is not realized.
Rotat
io
n
R
ot
ati
on
R
ot
ati
on
Rotat
io
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
Three fan wheel diameters
One fan
wheel
diameter
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
ATIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
Single Fan Installation
Rotat
io
n
R
ot
ati
on
R
ot
ati
on
Rotat
io
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
1 Fan
Wheel
Diameter
3/4 to one
fan
wheel
diameter
3/4 to one
fan
wheel
diameter
3/4 to one
fan
wheel
diameter
One fan
diameter
3/4 to one
fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
ATIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
Rotat
io
n
R
ot
ati
on
R
ot
ati
on
Rotat
io
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
Three fan wheel diameters
One fan
wheel
diameter
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
ATIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
Parallel Fan Installation
System Set-Up
Installations with inlet or discharge configurations that
deviate from this manual may result in reduced fan
performance. Restricted or unstable flow at the fan
inlet can cause pre-rotation of incoming air or uneven
loading of the fan wheel, yielding large system losses,
increased sound levels and structural failure of the fan
wheel. Free turbulent flow in the discharge ductwork
will also result in system effect losses. Refer to the
following diagrams for the most efficient installation
conditions.
Ducted Inlet Installations
Inlet Duct Turns
- Installation of a duct turn or elbow
too close to the fan inlet
reduces fan performance
because air is loaded
unevenly into the fan
wheel. To achieve full fan
performance, there should
be at least three fan wheel
diameters between the
turn or elbow and the
fan inlet.
Inlet Spin
- Inlet spin is a frequent cause of reduced
fan performance. The change in fan performance is a
function of the intensity of spin and not easily defined.
The best solution is proper duct design and airflow
patterns. Turning vanes reduce the effects of inlet spin.
Rotat
io
n
R
ot
ati
on
R
ot
ati
on
Rotat
io
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
Three fan wheel diameters
One fan
wheel
diameter
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
ATIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
Rotat
io
n
R
ot
ati
on
R
ot
ati
on
Rotat
io
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
Three fan wheel diameters
One fan
wheel
diameter
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
ATIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
Rota
tio
n
R
ot
ati
on
R
ot
ati
on
Rota
tio
n
Turning
Vanes
Turning
Vanes
POOR
POOR
GOOD
POOR
GOOD
Length of Straight Duct
GOOD
Three fan wheel diameters
One fan
wheel
diameter
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
SYSTEM EFFECT FACTORS CURVES
ST
A
TIC PRESSURE LOS
S
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
45
FPM X 100
OUTLET VELOCITY
CUR
VE
1
CUR
VE
2
CUR
VE
3
CUR
VE 4
