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turfserf

Least-bad way to make 90° turn in bathroom vent duct

turfserf
10 years ago

I'd like to install one of the highly-rated Panasonic WhisperCeiling vent fans in a bathroom ceiling. All the information I have found recommends that the fan be oriented in the ceiling to make a straight path for the exhaust duct to the outside wall. The fan's exhaust outlet from the fan runs parallel to the joists, so to have a straight path, the joists have to run perpendicular to the outside wall. But my joists run parallel to the outside wall, and so I will have to make a 90-degree turn.

Everything I read says to avoid a 90-degree turn right off of the fan, but It looks like that is what I will have to do. What is the best way to make the turn? Should I use a 2-foot length of flexible duct to come out of the fan and make the turn? Use 45-degree elbows? Or just use a 90-degree elbow? I will use rigid duct for the straight part of the run, which will be less than 5 feet.

I plan to use a 110 CFM fan, although I could get away with one as small as 50CFM. I hope the additional capacity will make up for the 90-degree turn.

Is the 90-degree turn a big deal?

Thanks.

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