Revised 6/11/18 Copyright © 2018 Trade-Wind Manufacturing, LLC Proverbs 22:29 Page 11
Duct Pipe and Fitting Sizes
(Continued)
Duct Runs – Length
a.
Configure the ventilation duct run to be as short and as direct to the outside as possible. Minimize
the number of elbows and transition fittings used. Complex or long runs should be reviewed by a
qualified installer.
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 390CFM 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.
d.
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.
390CFM Models
390CFM models have a 7" round duct.
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 recirculate the exhaust air back into the kitchen, be sure to remove the aluminum damper blade
before attaching the duct to the damper frame.
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.
In-line Damper
(for ventilation systems utilizing a roof cap or wall cap
without
a built-in damper)
In cold weather areas, installing an “in-line” damper may be the preferred type of installation. This is
because in-line dampers installed just above the perimeter of the heated space (the ceiling) will
reduce the amount of cold air traveling down the duct into the heated space and into the kitchen
through the ventilator.