Design Criteria
Duct System Costs
Duct Construction
Leakage Calculations
A New Problem for Rectangular Duct System
Spiral and Flat Oval Duct
Duct Heat Gain
Noise Control
 

The rectangular duct exceeds the estimated leakage of 400 cfm by 487 cfm (887 - 400), so that the duct system now requires about 21,000 cfm from the supply air fan.

This increase in fan volume will cause slight increases in system velocities and static pressures. To be pi prudent, the system designer should increase the initial rectangular duct pressure classification to 4 in w.g.... to allow for pressure increases that could occur with system balancing, as the calculated system static pressure drop was 2.98 in w.g.

The changes to a 4 in w.g. rectangular duct pressure class also would reduce the leakage for that portion of duct by half because of the "A seal class", cut the costs (and weight) of that part of the rectangular duct system would increase above those shown in Figure 2.

Duct gauge and reinforcement would change from H-18 to I-16. Another option would be to seal all rectangular ducts to "A seal class".

The initial round spiral ductwork specified can handle up to 10 in. w.g., so no change would be required even if there were major duct system pressure increases due to the balancing work.