Installation Guide

b. No portion of the ducting should be run so that the exhaust air flows downward. Since exhaust heat

rises, forcing the air to flow downward will cause increased static pressure. As previously mentioned,

improperly installed duct pipe will cause excessive static pressure (air resistance), that may result in

rattling, vibration and air buffeting noises, as well as inadequate ventilation.

c. Duct runs for 240 CFM ventilator models should not exceed 15 linear feet with one 90-degree elbow

(or two 45-degree elbows), a damper and a roof or wall cap. Longer runs or additional elbows will

result in decreased ventilation performance. Each 90-degree elbow is the equivalent of 8 linear feet

of duct pipe; each 45-degree elbow is equivalent to 4 linear feet of duct pipe.

d. Duct runs for 390 CFM ventilator models should not exceed 20 linear feet with two 90-degree elbows

(or four 45-degree elbows), a damper and a roof or wall cap. Longer runs or additional elbows will

result in decreased ventilation performance. Each 90-degree elbow is the equivalent of 8 linear feet

of duct pipe; each 45-degree elbow is equivalent to 4 linear feet of duct pipe.

e. Duct runs for 600 – 1200 CFM ventilator models should not exceed 35 linear feet with two 90-degree

elbows and two 45-degree elbows, a damper and a roof or wall cap. Longer runs or additional elbows

will result in decreased ventilation performance. Each 90-degree elbow is the equivalent of 6 linear

feet of duct pipe; each 45-degree elbow is equivalent to 3 linear feet of duct pipe.

f. Always run ventilator ducts to the outdoors. DO NOT terminate a duct into an attic, basement,

garage, crawl space under a house, a chimney, other ducting or an enclosed room.

4. Dampers

IMPORTANT: DO NOT USE SCREWS TO ATTACH ANY TYPE OF DAMPER AS THE SCREWS MAY BLOCK THE

DAMPER BLADES.

IMPORTANT: DO NOT USE MORE THAN ONE DAMPER IN THE VENTILATION SYSTEM. NOTE: Many styles of

roof caps and wall caps have built-in dampers. See Roof Caps and Wall Caps section for more detail.

Always use carefully crafted, tightly wrapped Aluminum Foil Metal Duct Tape on all connections and physically

view and test the damper blades to make certain they are opening and closing correctly. Make sure that the

damper blades do not touch the duct walls and that there is no debris blocking the free movement of the

damper mechanism. Common things to look for include screws protruding into the blade’s path, overspray of

paint, plaster and insulation. If using rectangular duct, be sure that all four sides of the duct are on the

outside of the damper’s start collar or frame.

a. 390 CFM Models

390 CFM models have either a 3.25” x 10” rectangular metal damper attached directly to the

ventilator or a 7" start collar that requires a 7" damper (sold separately). DO NOT USE SCREWS TO

ATTACH THE DUCT TO THE DAMPER FRAME AS THE SCREWS MAY BLOCK THE DAMPER BLADE.

ALWAYS use Aluminum Foil Metal Duct Tape on all connections and physically view the damper blade

to make certain it is operating correctly. On ventilator installations designed to re-circulate the

exhaust air back into the kitchen, be sure to remove the aluminum damper blade before attaching the

duct to the damper frame.

600 – 1200 CFM Ventilator Models

Damper in Roof Cap or Wall Cap

In ventilation systems utilizing a roof cap or wall cap with a built-in damper, do not install an additional in-line

damper. Two dampers are unnecessary and will cause increased static pressure (air resistance), that may

result in rattling, vibration and air buffeting noises, as well as inadequate ventilation.