5
Planning the Installation
Planning the Ductwork
wArning
• To prevent combustion by-products, smoke or odors
from entering the home and to improve efficiency, tape
all duct joints securely.
• Use only ductwork deemed acceptable by state,
municipal and local codes.
• Range hoods may interrupt the proper flow of smoke
and combustion gases from furnaces, gas water heat-
ers and fireplaces. To avoid drawing lethal gases into
the home, follow the manufacturer’s recommendation
for these devices and consult NFPA and ASHRAE rec-
ommendations.
• Failure to install proper ductwork may result in a back
draft and/or the insufficient venting of smoke and
fumes.
•
do not
install an additional in-line or external blower
to increase the length of the duct run. Even small dif-
ferences between blower air flow rates can greatly
reduce the air draw by the hood.
•
cAution
-
To reduce the risk of fire and to properly
exhaust air, be sure to duct air outside the house or
building. Do not vent exhaust air into spaces within
walls or ceilings or into attics, crawl spaces or garages.
• For optimal performance, consult a qualified HVAC
specialist when designing the duct system.
• All ductwork materials (including screws and duct tape)
must be purchased separately by the customer. When
planning new ductwork, always look for the shortest,
most direct route to the outside.
• The exhaust connects to 8-inch dia. round duct. You
may increase the duct size over the duct run if desired.
To prevent a back draft, never decrease the duct size
over the run. If existing ductwork is smaller than 8 inch-
es, remove and replace with 8-inch ductwork.
• Do not rely on tape alone to seal duct joints. Fasten all
connections with sheet metal screws and tape all joints
with certified silver tape or duct tape. Use sheet metal
screws as required to support the duct weight.
• To prevent back-drafts, a damper at the duct outlet may
be required. Make sure ductwork does not interfere
with floor joists or wall studs.
Calculating the Maximum Duct Run Length
The maximum straight duct length for the hood is deter-
mined by the type of duct used. See the chart below.
duct siZe
mAXimum duct run
8” round
60 feet
10” round
50 feet
3¼” X 10” rectangular
50 feet
For each elbow and transition added to the ductwork, a cer-
tain number of feet must be subtracted from the maximum
duct run to compensate for wind resistance. To determine
the length the ductwork cannot exceed, subtract all of
the equivalent lengths of the elbows and transitions listed
below from the maximum duct run above.
Ductwork Equivalent Lengths
eQuivAlent lengths (nominAl)
piece
subtract
piece
subtract
8” 90° elbow
7 feet
10” 90° elbow
5 feet
8” 45° elbow
3 feet
10” 45° elbow
2 feet
3¼” X 10”
to round 90°
transition
25 feet
3¼” X 10” to
8”/10” round tran-
sition
4 feet
3¼” X 10”
90° elbow
15 feet
3¼” X 10”
90° flat elbow
20 feet
3¼” X 10”
45° elbow
7 feet
Roof cap or wall
cap with damper
*
* The equivalent lengths of roof and wall caps vary with
model and configuration. For equivalent length, contact the
manufacturer or a qualified HVAC specialist.
Ductwork Design Tips
Wherever possible, reduce the number of transitions and
turns to as few sharp angles as possible. Two staggered
45° angles are better than one 90°.
Keep turns as far away from the hood exhaust as possible,
and as much space between bends as possible.
For best performance, use round duct instead of rectangu-
lar, especially when elbows are required.
If multiple elbows are used, try to keep a minimum of 24
inches straight duct between them.
Avoid “S” or “back to back” use of adjacent elbows.
In regions where the weather gets extremely cold, use ther-
mal breaks, such as a short section of non-metallic duct, to
avoid indoor heat loss. Locate the break as close as pos-
sible to the outside pass through point.
Do not use flexible metal duct.
Do not use ductwork that is smaller in cross-sectional area
than the recommended types above.
fan
fan
elbow (not
included)
