Installation Instructions Revised 10/13/2015 Copyright (C) 2008 Proverbs 22:29 Page 11
11
9.
Duct Sizing Chart and Area Calculations
Ventilator Discharge Port
Types & Sizes
Duct Type Required
Duct Size
(in Square Inches)
Minimum Discharge Size
of Roofcap or Wallcap
Outside Opening
6” Diameter, Round
28.3”
6” Round Metal Duct
28.3”
28.3”
7” Diameter, Round
38.5”
7” Round Metal Duct
38.5”
38.5”
8” Diameter, Round
50.25” 8” Round Metal Duct or
6” x 9” Rectangular Metal Duct
50.25”
54”
50.25”
54”
10” Diameter, Round
78.5”
10” Round Metal Duct
78.5”
78.5”
3.25” x 10” Rectangular
32.5”
3.25” x 10” Rectangular Metal Duct
32.5”
32.5”
Calculating Square Inches of Various Duct Sizes & Types
ROUND DUCT
RECTANGULAR DUCT
Radius x Radius x 3.1416 = Area (Sq. Inches)
Width
x
Depth
=
Area (Sq. Inches)
x
x
=
x
=
The “radius” is one-half the diameter of a round duct,
e.g., ½ of a 10” round duct is 5”. 3.1416 is “Pi”, the
“constant” used when calculating the area of a circle.