The box is usually referred to as a vacuum plenum and this can work. You'll need to consider a couple of things. For anything approaching balanced draw on both hoods you'll need to be sure that the hood setups are identical. Used 8 inch rigid duct as a minimum going to your hoods, 10-12 inch on your exhaust stack. Calculate your fan power requirements based on getting a minimum draw of 125cfm/sq. ft. on both hoods. Don't forget to include the the bends in your ducts (including the ducts from the hoods as well as any bends in the exhaust stack and the stack cover if it's held open by air pressure) into your static pressure calculations - they will increase the power requirement on your fan. You may need a bigger blower to drive this system. Don't forget to provide for adequate make up air.
Robert
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Robert Simmons
(Former) Director for Bead Donations
Beads of Courage, Inc.
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