Can you have 2 bends in ducts for a bathroom shower fan?

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agm413

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In my townhouse the ceiling joists are parallel to the exterior walls, so in order to use a generic ceiling mounted bathroom fan it would either need to be tall to be above the joists, or run for a few feet, then bend up, then bend again over the joists in order to go to the exterior wall. Is that an okay setup for the ducts? They would be air sealed and insulated to avoid condensation.

Main reason I don't want to go through the roof is because it is a low slop roof and it is on the low side, so that area gets the most water of any part of the roof.

Thanks for any advice and can provide clarification as needed.

Thanks!
 

wwhitney

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The fan manual should tell you the maximum allowable duct length based on the diameter and type of duct. It should also include an equivalent length for each 90 degree elbow you use. That will tell you if the geometry you want is OK with the normal size duct, or if you would need to upsize the duct to compensate for the length.

Rigid metal duct, air sealed (including every joint of an adjustable elbow), with insulation outside would perform better than flexible duct. You'd still want to slope the duct ever so slightly so that should any condensation occur it is not trapped in the middle of the duct run.

Cheers, Wayne
 

agm413

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The fan manual should tell you the maximum allowable duct length based on the diameter and type of duct. It should also include an equivalent length for each 90 degree elbow you use. That will tell you if the geometry you want is OK with the normal size duct, or if you would need to upsize the duct to compensate for the length.

Rigid metal duct, air sealed (including every joint of an adjustable elbow), with insulation outside would perform better than flexible duct. You'd still want to slope the duct ever so slightly so that should any condensation occur it is not trapped in the middle of the duct run.

Cheers, Wayne
Thank you, much appreciated!
 
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