Hi. We are trying to upgrade our range hood as part of a kitchen remodel. Our current system vents via one 3.25x14 rectangular duct, down through the wall behind the range, then transitions to a 6" round under the house.
My range wall is a standard 4" depth, studs on 16", so 3.25x14 seems to be the largest rectangular duct the wall can facilitate.
The new hood is more powerful - 640cfm - requiring a minimum 8" round or equivalent. According to this website (http://www.engineeringtoolbox.com/eq...ter-d_205.html) the equivalent rectangular duct would need to be larger than 3.25x14; larger than my interior space between the studs and drywall.
So my question is, can I run TWO 3.25x14 rectangular ducts parallel to eachother in the wall (stud separating them) to meet minimum airflow? I realize I would have to join them at the top somehow, and not sure how to calculate the resistance of splitting the airflow like that. (The new hood has a 10" round vertical exhaust port at top, so I must make a 180 degree transition from that, to the two 3.25x14 rectangular ducts). Once under the house, the two rectangulars would rejoin/transition to a single 8-10" round to run out of the house.
Any tips are much appreciated. Jay