User Manual

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 dual blower unit (WM2L, used in all systems) requires 8” round duct or equivalent (50 square

inches). The single blower unit (WM1L, used in addition to the dual blower unit in 900 CFM

systems) requires 6” round duct or equivalent (28 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 (DO’S AND DON’TS)

• 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.

Smooth duct Smooth gradual turn

Proper combining

of two ducts

YES

Flexible duct Sharp angled turns

of two ducts

Improper combining