All specifications subject to change without notice.
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PLANNING
GUIDE
DH
Distinctive 30 and 36” Wide
Wall Mount Range Hood
Document # PG07-007
Revised 05/22/13 Page 2/2
Planning the Duct work
■
For optimal performance, consult a qualified HVAC specialist when
designing the duct system.
■
All duct work materials (including screws and duct tape) must be
purchased separately by the customer.
■
When planning new duct work, always look for the shortest, most
direct route to the outside.
■
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 duct work is smaller than 8 inches, remove and replace with
8-inch duct work.
■
To prevent back-drafts, a damper at the duct outlet may be required.
Make sure duct work does not interfere with floor joists or wall studs.
Duct work 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 rectangular,
especially when elbows are required.
■
If multiple elbows are used, try to keep a minimum of 24” straight duct
between them. Avoid “S” or “back to back” use of adjacent elbows.
■
In regions where the weather gets extremely cold, use thermal
breaks, such as a short section of non-metallic duct, to avoid indoor
heat loss. Locate the break as close as possible to the outside pass
through point.
■
Do not use flexible metal duct.
■
Do not use duct work that is smaller in cross-sectional area than the
recommended types above.
Calculating the Maximum Duct run Length
The maximum straight duct length for the hood is determined by the type of
duct used. See the chart below.
For each elbow and transition added to the duct work, a certain number of
feet must be subtracted from the maximum duct run to compensate for wind
resistance. To determine the length the duct work cannot exceed, subtract
all of the equivalent lengths of the elbows and transitions listed below from
the maximum duct run above.
Duct work Equivalent Lengths
Equivalent number of Feet -
Duct Elbows and Transitions
45° elbow, 8 inch
3 feet
3 ¼” X 10”, 45° elbow
7 feet
45° elbow, 10 inch
2 feet
3 ¼” X 10”, 90° elbow
15 feet
90° elbow, 8 inch
7 feet
3 ¼” X 10”, 90° flat elbow
20 feet
90° elbow, 10 inch
5 feet
3 ¼” X 10” to 8” round
transition
4 feet
90° 3 ¼” X 10” to
8” round transition
25 feet
3 ¼” X 10” to 10” round
transition
4 feet
Roof cap
*
Wall cap**
*
* The equivalent lengths of roof and wall caps vary with model and
configuration. For equivalent length, contact the manufacturer or a qualified
HVAC specialist.
fan
fan
elbow (not
included)
Duct Size
Maximum Straight
Duct run
8” round
60 feet
10” round
50 feet
3¼” X 10” rectangular
50 feet
