What's the best material for bathroom exhaust fan duct?


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Old 06-20-15, 06:09 PM
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What's the best material for bathroom exhaust fan duct?

I'm installing a bathroom exhaust fan in my half bath - no tub or shower just sink and toilet.

In looking at a lot of how to's online I see a lot of people using flexible duct. I understand this is not the best material.

I've also seen people recommend pvc schedule 40 as the best option.

I used galvanized steel for my dryer vent and the pipe rusted through though people seem to think it's better than aluminum.

So my question, what is the best material to use for a bathroom vent duct?

Once I put up the ceiling I will not have access so I want something that will last forever. No real moisture so rust is less of a concern.

Thanks!
 
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Old 06-20-15, 06:22 PM
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Flex will work fine.
Was that dryer vent run though an attic with no insulation on the pipe and not ran down hill to the vent?
My galvinized pipes been there over 20 years and there's no rust.
Aluminum if fine for a bathroom vent but would burn through in seconds in a dryer fire.
 
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Old 06-20-15, 07:02 PM
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PVC schedule 40 gets my vote in that if you cannot access the pipe after you install it. Properly glued and supported it should last longer than the house I would think.
 
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Old 06-20-15, 07:02 PM
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Thanks. The dryer vent was in my basement that is 1/2 below grade. It gets pretty cold in the pipe but the room is warm. The back side may have been touching the concrete foundation wall so that may have had something to do with it.
 
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Old 06-20-15, 08:44 PM
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Ron,

Do I need any special adapters to attach the Pvc to the fan outlet and the vent with the tin pipe on the outside?

Pvc may look better as some of the pipe will be exposed in the adjacent boiler room.
 
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Old 06-21-15, 05:52 AM
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You will want to use a semi rigid metal flexible duct like this - Speedi-Products 4 in. x 96 in. Heavy Duty UL 2158A Flexible Round Aluminum Transition Pipe-EX-MTF 496 - The Home Depot

You may need a reducing collar depending on the size outlet for your fan and the vent cover where it exits the building. Remember, you can not vent straight into an attic space, it must exit to the outside.
 
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Old 06-21-15, 06:40 AM
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Whatever you use, based on your location, you need to insulate the duct.
 
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Old 06-21-15, 07:32 AM
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The flexible metal duct would sure be easier, but is that the best installation I need to do?

Insulation is not required as it is not going through an attic - the ceiling is directly under the first the floor of the room above it so it's warm space. Correct?

I do have an upstairs bath fan duct that runs through an uninsulated attic. It sounds like I should switch that pipe to insulated.
 
 

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