Bathroom Exhaust Fan Duct Support

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Hdmstng

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I'm looking to install an 80 CFM Broan XB80 bathroom exhaust fan in our first floor bathroom (5' x 12'). The bathroom was built with no fan and I will have no access from above. Duct can be either 6" or 4" as well. I plan to run the duct parallel to the floor joists and out the side of the house, which is just under 14'. The duct will go 2.5' across the bathroom, then another 11' across the bedroom and out.

I'll only have access from the outside and through the hole for the fan, but I could slide the entire duct in from the outside. My issue is will the duct sag and how do I support the the duct without having to cut out the ceiling in the bedroom to install straps?

Would thin walled PVC be a good option? It could be solvent welded to nearly the entire length (no worries for condensation leaks) and slide in as a single unit. Would use a short flexible house to attach to the fan housing and should be able to get a strap in at the fan end.

What other options should I consider?

Thanks,
HD
 

Cacher_Chick

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I never use anything but rigid smooth-wall galvanized sheet metal duct. The flexible plastic or aluminum duct is complete junk, and almost impossible to install in such a way that will prevent condensation from pooling in the tubing.
 

Hdmstng

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I'll definitely be staying away from the flexible material, except to make the connection from the fan to the regular duct. From what I have read, the flexible stuff helps to dampen vibrations. But you only need a very short amount, 1/2 a foot or so.

Since rigid smooth-wall galvanized sheet metal duct comes in sections, and even after using sheet metal screws and foil tape, will it have a tendency to droop or sag? I'll have about 12-13 feet that will be supported at the ends, since I won't be able to put straps in.
 

CountryBumkin

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I like the idea of 4-inch thin-walled PVC (regular sch40 would be too heavy). No corrosion to worry about and smooth enough inside so condensation won't build up.
Were can you buy this and are there matching 45* or 22-1/2* fittings available? if it's not readily available, then the galvanized heater-vent pipe would be my next choice (over the flexible accordion-like stuff that HD sells. Assuming you had that as a choice).

UPDATE: Okay, schedule 20 PVC (for dust collection) is very hard to find. So maybe the galvanized metal HVAC ducting is the way to go (then just wrap insulation around it. Need to research pipe insulation now).

http://www.thegeekpub.com/3492/where-to-buy-schedule-20-pvc-for-dust-collection/
 
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