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OTR microwave exhaust ducting size

732 Views 1 Reply 2 Participants Last post by  oh'mike
the installation instructions calls for 6" diameter ducting and the ducting should not exceed 120 equivalent feet.

the problem is i can not exhaust vertically through the roof because the ducting would be visible so will be vented horizontally through the kitchen wall. HOWEVER, the space won't accommodate a 6" diameter duct. can i use 4" diameter ducting at significantly reduced equivalent feet of run and not create too much back pressure on the exhaust fan?

6" diameter pipe has 2.25 times greater sectional area than a 4" diameter soooooo i was thinking that if i used a maximum of 50 equivalent feet of run, i should be ok?
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I moved this to HVAC for you--those folks know ducting best.

Can you get a 3 1/4" x 10" into the space? That will not cut down on the flow.
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