Page 2
(Rev. 04/08)
L114A
Ducting Do’s and Don’ts NEVER restrict the duct size. The K250 blower unit requires 7” round duct or equivalent (32.5
square inches). Using Vent-A-Hood transitions (back page) will ensure proper efficiency.
Do not use flexible or corrugated duct. This type of duct will restrict airflow and reduce
performance. Only use smooth, galvanized, metal duct. Observe local codes regarding special
duct requirements and placement of duct against combustibles. 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. A 90 degree elbow is
equal to 5 feet of duct. Using Vent-A-Hood roof jacks or wall louvers (back page) will ensure
proper efficiency. Airflow must not be restricted at the end of the duct run. Do not use screen
wire or spring-loaded doors on wall louvers or roof jacks. Do not terminate venting into an attic
or chimney. Where possible, seal joints with duct tape. The hood must be ducted to the outdoors
without restrictions.
Blower Duct Size Sq. Inch Area
K250 3 1/4” x 10” rectangular or equivalent 32.5”
YES
NO
Smooth Duct Smooth Gradual Turn
Flexible Duct Sharp Angled Turns