38 square inches "true" net free area, calculated according to SMACNA specification.
Available in musket brown, black and gray (pre-painted), also available in paint ready aluminum-zinc coated
Removable hood attached by 4 slotted hex-head sheet metal screws
Specs:
Flange is 4 1/'2" from throat
Base is 2.5# lead, 18" x 18"
Hood is 10 1/2" x 10 1/2"
Painted metal is .016 (underlying thickness is equal to G-90)