Use & Care Guide

PLANNING
GUIDE
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Specications are subject to change without notice.
See installation instructions for additional details.
6.1
Duct Planning Guide
DUCT PLANNING GUIDE
PLANNING
GUIDE
Document # PG06 - 001 Revised 10/21/09 Page 1/1
WARNING
All blowers, hoods and raised vents must be installed in •
accordance with the accompanying installation instructions.
Observe all governing codes and ordinances during planning •
and installation. Use only duct work deemed acceptable
by state, municipal and local codes and by the installation
instructions. Contact your local building department for
further information.
To prevent combustion by-products, smoke or odors from •
entering the home and to improve efficiency, tape all duct
joints securely.
Hoods and vents may interrupt the proper flow of smoke •
and combustion gases from furnaces, gas water heaters
and fireplaces. To avoid drawing lethal gases into the home,
follow the manufacturer’s recommendation for these devices
and consult NFPA and ASHRAE recommendations.
Improper installation may result in a back draft and/or the •
insufficient venting of smoke and fumes.
For hoods or raised vents equipped with integral blowers, •
DO NOT install an additional in-line or external blower to
increase the length of the duct run. For hoods or raised vents
not equipped with integral blowers, DO NOT install more
than one in-line or external blower. Even small differences
between blower air flow rates can greatly reduce the air
draw.
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.
General Design Requirements
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. Some
models can accommodate venting (and/or wiring) through the back.
To prevent a back draft, never decrease the duct size over the run. If ◊
existing duct work is smaller than 8 inches in diameter, remove it and
replace it with 8" round, 10" inch round or 3 1/4" x 10" duct work. Do
not use duct work that is smaller in cross-sectional area than these
recommended types. Do not use flexible metal duct.
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 also be ◊
required.
Make sure duct work does not interfere with floor joists or wall studs.◊
On dual exhaust models, the two 8” exhausts may be merged ◊
into one 10” duct using a Dacor transition kit. See the installation
instructions for details.
With concrete slab construction, "box-in" the duct work to prevent it ◊
from collapsing when the wet concrete is poured. Also allow room for
electrical conduit.
Calculating the Maximum Duct Run Length
The maximum straight duct length is determined by the type of ◊
hood or raised vent installed and type of duct used. See the hood or
raised vent specifications for the maximum duct run for the desired
configuration.
To determine the actual length the duct work cannot exceed, subtract ◊
all of the equivalent lengths of the elbows and transitions listed
below from the maximum straight duct run from the hood/raised vent
specifications. After determining that your proposed duct work meets
the maximum duct length requirement, proceed with the location
planning.
Equivalent Lengths
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
transition
4 feet
3 ¼” X 10"
45° elbow
7 feet
3 ¼” X 10"
90° elbow
15 feet
3 ¼” X 10"
90°atelbow
20 feet
Roof cap *
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.
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°.
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.
Keep turns as far away from the hood or raised vent 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.
Cross-drafts or air currents caused by adjacent open windows or ◊
doors, HVAC outlets, ceiling fans and recessed ceiling lights reduce
vent efficiency.