Originally Posted by
mardoman
If I recall this correctley an island hood open on all four sides requires 150 cfm per sq.ft.
A hood against a wall require 100 cfm per sq.ft.( open on three sides ).
Using your size : 17 x 4 = 68 sq. ft. x 100 cfm = 6800 cfm.
The exhaust velocity needs to be 1500 fpm.
Make-Up Air (supply) needs to be approx. 80% at the hood.
Using your size hood, 6800 cfm x 80% = 5440 cfm
The buiding (kitchen) pressure needs to be neutral or slightly positive.
With your hood, that means 6800 cfm - 5440 cfm = 1360 cfm of fresh air is still required to be supplied to building. Generally advised to be supplied thru economizers from Roof Top Gas Pak or A/C.
This should help you pick the correct sized Make-Up Air Ventilator. Then you must size the duct based on the static. The Mfg. of the ventilator will be able to help you size this up.