Thread: Bathroom fan ducting question

Hey all.

I'm looking at putting a bathroom fan into a 50's era, single-story house that currently doesn't have one. The options appear to be vent to the roof, or vent through the gable. Being concerned with introducing a leak in the roof, I'm leaning toward the gable vent.

1) Do I actually have the choice of where to vent? (i.e. if it's the attic and not between floors, am I required to vent to the roof)
2) If I vent through the gable, am I allowed to run the duct over the joists, or do I need frame something in around the ductwork?

thank you!

chris

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Originally Posted by Chris Hoover

Hey all.

I'm looking at putting a bathroom fan into a 50's era, single-story house that currently doesn't have one. The options appear to be vent to the roof, or vent through the gable. Being concerned with introducing a leak in the roof, I'm leaning toward the gable vent.

1) Do I actually have the choice of where to vent? (i.e. if it's the attic and not between floors, am I required to vent to the roof)
2) If I vent through the gable, am I allowed to run the duct over the joists, or do I need frame something in around the ductwork?

thank you!

chris

1)Yes, it is your choice, I prefer the gable

2) Yes, you are allowed to run the duct over the joust.
You can also hang the duct from the rafters.
Note
Insulate the duct
Droops or dips in the duct will catch water.

Ideally the duct will be galvanized sheet metal and not flexible aluminum or vinyl. It must terminate at a dampered hood at the roof, side wall, or soffit. The shorter the duct run the better it will work. Reference the fan manufacturer's installation instructions, IRC 102.4 and 303.3, if applicable in your area.

Number 3, don't use that cheap plastic duct tape (duck tape) that melts in the heat and allows the pipe to fall back into the attic. Use metal foil tape or screw and clamp everything.

Originally Posted by Aaron Miller

Ideally the duct will be galvanized sheet metal ...

And support the duct at each section. That will take the weight off of the connection joints, which are not designed to carry the weight of the duct anyway, the joints are intended to be sealed and leak-free, you don't want the joints to pull apart.

Originally Posted by Jerry Peck

And support the duct at each section. That will take the weight off of the connection joints, which are not designed to carry the weight of the duct anyway, the joints are intended to be sealed and leak-free, you don't want the joints to pull apart.

10'-0" o.c. as per IRC 1601.3.2?

I can't recall ever seeing a solid metal vent pipe used for a bathroom vent. Not saying it is a bad idea, I just can't recall ever seeing it done. All I see are flex vinyl, flex alum foil vents or Mylar type vent pipes.

Originally Posted by Scott Patterson

I can't recall ever seeing a solid metal vent pipe used for a bathroom vent. Not saying it is a bad idea, I just can't recall ever seeing it done. All I see are flex vinyl, flex alum foil vents or Mylar type vent pipes.

Same here

The flexible vinyl ducts trap dust and go moldy. I'll post some pics.

Here's a pipe full of crud that blew off as well. Actually, it looks like somebody covered the fan purposely. Whatever.

Originally Posted by Scott Patterson

I can't recall ever seeing a solid metal vent pipe used for a bathroom vent. Not saying it is a bad idea, I just can't recall ever seeing it done. All I see are flex vinyl, flex alum foil vents or Mylar type vent pipes.

The production builders here put in whatever they find on the truck. The better builders install only sheet metal. Some of the AHJs require sheet metal. Most don't know the difference.

Thank you all so much for your input. I really appreciate it!

Chris