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GAUGES FOR AVERAGE LOCAL EXHAUST
SYSTEMS
 U.S. STANDARD GAUGE STEEL DUCT
For aluminum duct - Use 2 gauge numbers heavier.
Elbows and angles should be a minimum of two gauges heavier than straight lengths
of equal diameter. Hoods should be a minimum of two gauges heavier than straight section of connecting branches.
Special consideration must be given to corrosive applications.
CLASS I Includes non-abrasive
applications such as paint spray, woodworking, pharmaceutical, LAUNDRY and food products, and discharge ducts from
dust collectors.
Please be advised that all ducting turns should be slow radius turns. Even with this type of bend, when considering back pressure issues, every turn is equal to approximately 100 feet of straight ducting. To avoid back pressure issues, limit the number of bends to a minimum or eliminate them completely. A WORD OR TWO ABOUT CO-AXIAL DUCTING This ducting system is designed so that the inlet air must travel around the outside of the exhaust duct work. The theory is that the incomming air will be heated by the exhaust ducting, lowering the amount of gas required to bring it up to temperature. Check out Web-sites for Fairfield Manufacturing (FLM) or Thermal Engineering of Arizona (TEA) for examples. These systems are fairly expense when compared to standard ducting. Be sure that you study the benefits, closely. If your average temperature is above 70 degrees, would it make sense that your incomming 70 degree air is more difficult to heat to 500+ degrees than preheated 100 degree air might be? If anyone has any test data on the benefits of co-axial duct, I'd love to post it. I'd like to know the metered difference between equal dryers performing similar formulas, one with co-axial and the other without.
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