11
Installation Specifications
Calculating Maximum Duct Run Length
• For best performance, consult a qualified HVAC specialist
when designing the duct system.
• Do not use duct work that is smaller than the required
sizes in the tables below.
• For best performance, keep the duct run as short as pos-
sible, and
never
exceed the maximums in the table in the
Duct Work Design Tips
section.
• The max. duct length for the downdraft vent depends on
the blower used, and number of elbows and transitions.
The
Equivalent Number of Feet
for each elbow and
transition must be subtracted from the maximum straight
length to compensate for wind resistance. To decide the
maximum allowable length of the ducting, subtract all
equivalent lengths of the elbows and transitions listed
below from the
Blower Maximum Duct Straight Length
.
Example: For a downdraft vent system using a 3¼ x 10
rectangular duct, two (2) 3¼ x 10 90° elbows, a 3¼ x
10” rectangular to 10” round transition, and a REMP16
remote blower:
• From the
Blower Maximum Duct Straight Length
table,
the max length without transitions and elbows is 60 ft.
• The equivalent length of each 90
°
elbow is 15 ft.
• The equivalent length of 45
°
elbow is 2 ft.
• The equivalent length of the transition is 4 ft.
• The total equivalent length of the above parts is: 15 ft +
15 ft + 4 ft + 2 ft = 36 ft.
• The max amount of straight duct that can be used with a
REMP16 and the above parts is: 60 ft – 34 ft = 24 ft.
Equivalent Number of Feet (Nominal) -
Duct Elbows and Transitions
45° elbow/8”
3 ft
3¼ x 10/45° elbow
7 ft
45° elbow/10”
2 ft
3¼ x 10/90° elbow
15 ft
90° elbow/8”
7 ft 3¼ x 10/90° flat elbow 20 ft
90° elbow/10”
5 ft
3¼ x 10 to
8” round transition
4 ft
90° 3 ¼ x 10 to
8” round transition 25 ft
3¼ x 10 to
10” round transition
4 ft
Roof cap
*
Wall cap**
*
*Equivalent lengths of roof and wall caps vary with model and
configuration. For equivalent length, contact the manufacturer or
a qualified HVAC specialist; **Not applicable to REMP blowers.
Duct Work Design Tips
• Reduce transitions and turns to the fewest sharp angles.
Two staggered 45° angles are better than one 90°. Keep
turns as far from the hood exhaust as possible, with the
most possible space between each bend.
• For best performance, use round ducting when possible,
especially when elbows are required.
• If multiple elbows are used, try to keep a minimum of 24”
of straight duct between them. Avoid “S” or “back to back”
configurations of adjacent elbows.
• Do not use flexible metal ducting.
Blower
Blower Maximum Duct Straight Length
8” Duct
10” Duct
3¼ x 10 Duct
CABP3
40 ft (12.2 m)
30 ft (9.2 m)
30 ft (9.2 m)
ILHSF8
50 ft (15.2 m) 40 ft (12.2 m) 40 ft (12.2 m)
ILHSF10
60 ft (18.3 m) 70 ft (21.3 m) 60 ft (18.3 m)
REMP3
50 ft (15.2 m) 40 ft (12.2 m) 40 ft (12.2 m)
REMP16
60 ft (18.3 m) 70 ft (21.3 m) 60 ft (18.3 m)
