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©2018 Hestan Commercial Corporation
10
EN
DUCTING DO’S AND DON’TS
GENERAL REQUIREMENTS
Observe local codes regarding special duct requirements and placement of duct work against
combustibles.
• Using recommended transitions (see VENT ACCESSORIES) will ensure proper efficiency.
• Using recommended roof caps or wall louvers (see VENT ACCESSORIES) will ensure proper
efficiency.
• Use foil HVAC tape (not grey cloth duct tape) to seal all joints.
• The hood must be ducted to the outdoors without restrictions.
BLOWER REQUIREMENTS
The single blower unit (WM1L, used in 900 CFM systems) requires 6” round duct or equivalent
(28 square inches), and the dual blower unit (WM2L, used in all systems) requires 8” round duct or
equivalent (50 square inches).
COMBINED DUCT SIZE AFTER A TRANSITION
Single and Dual (WM1L & WM2L) combine to 10” round or equivalent 79 sq. in. using a multi-
blower transition such as AKVT6810 (Optional).
Two Duals (Two WM2Ls) combine to 12” round or equivalent 113 sq. in. using a multi-blower
transition such as AKVT8812 (Optional).
DUCTING REQUIREMENTS
• NEVER reduce the duct size. When combining ducts together, the square inch area of
the outlet duct must be equal or greater than the total square inch area of the ducts being
combined.
• Only use smooth, galvanized, metal duct. Do not use flexible or corrugated duct. This type of
duct will restrict airflow and reduce performance.
• Make the duct run as short and as straight as possible with as few turns as possible.
• Avoid sharp-angled turns. Instead, use smooth, gradual turns such as adjustable elbows or 45
degree angled turns.
• For duct runs over 20 feet, increase the duct diameter by one inch for every ten feet of duct.
• When planning length, a 90 degree elbow is equivalent to 5 feet of duct.
TERMINATION REQUIREMENTS
Airflow must not be restricted at the end of the duct run.
A wall louver or roof cap is required for each duct run.
Every wall louver or roof cap must include a gravity damper to prevent back drafts.
Do not use screen wire or
spring-loaded doors on wall
louvers or roof caps.
Do not terminate venting into
an attic or chimney.
YES
NO
Smooth Duct
Smooth Gradual Turn
Proper Combining
of Two Ducts
Flexible Duct
Sharp Angled Turns
Improper Combining
of Two Ducts
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