Appendix G: VAV Open Area Guidelines
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Original instructions
c.
Free opening area
i.
Multiply the width opening times the vertical opening (A x
B), and enter that here:
Free opening area = ___________ square inches = C (sq.in)
ii.
Divide this by 144 to arrive at square feet, and enter that
here:
Free opening area = ____________ square feet = C (sq.ft)
2.
Determining bypass or “leakage” area
a.
This is the opening width (A) times 0.34 inches (A x 0.34 = bypass
area).
Bypass area = ___________ square inches = D (sq in)
b.
Divide this by 144 to arrive at square feet
Bypass area = ____________ square feet = D (sq ft)
3.
Determining Total Effective Opening Area
a.
This is the Free Opening Area plus the Bypass Opening Area
(C + D = Total Effective Opening Area)
Total Effective Area = _____________ square inches
Total Effective Area = _____________ square feet
* Industry standards call for sash height to be measured from the work surface, however, for the purposes of determining
free opening height, measurement is to be taken from the top of the lower airfoil sill to the bottom of the sash handle.
