EWC Controls Inc. 385 Highway 33 Englishtown, NJ 07726 800-446-3110 FAX 732-446-5362 E-Mail- [email protected]
9
FRESH AIR AND EXHAUST AIR DUCTING
SOME GENERAL RULES, GUIDELINES, AND SUGGESTIONS
1.
DO NOT install a fresh air intake duct/grille/register or hood, close to any type of exhaust system
discharge, plumbing/sewer vent pipes, or furnace flue pipes!
If it is unavoidable, make sure the fresh
air intake is low to the ground or roof line, and the exhaust/vent discharge is at least four (4) feet
higher than the intake. Check and Follow national and local mechanical codes and ordinances.
2. Use high quality intake or exhaust grilles & hoods with insect and rodent screens. Inspect and clean
them periodically.
3. Installing a separate outside air filter will help prolong the life of your standard return air filter.
4. Use
hooded
intake and exhaust fittings to stop rain or snow from falling into your duct.
5.
DO NOT install a return air damper or completely close off a return air damper, if your fresh air duct
is under-sized, or completely closed off!
Example:
Return air main is 20”x25” and you install an 8”
round fresh air duct & damper.....You will NOT install a return air damper.
6. In the above example, you really don’t need an exhaust damper either. An 8” round duct will
introduce approximately 210-275 cfm @ .08 - 0.1 friction factor. This additional air volume is enough to
provide a slight positive pressure to the home or office. Better for the home to be slightly positive than
negative. Insects have a harder time getting inside when the front or back door is opened.
Exhaust hood,
Flue pipe,
Sewer vent, etc.
Fresh Air Intake
4 feet Minimum
Check local code!
Typical
Gable &
Roof-line
Direct Vent
Flue Pipe
6 feet Minimum
Check local code!
Gable Vent
