Bath fan venting runs through attic and out side of house

ponch37300 · 09-24-2011, 11:26 AM

I am installing a new bath fan and have a couple quick(hopefully) questions.

I bought a broan fan with 4" outlet. Also bought a 4" siding vent for the side of the house. Now for piping them together. I will be going up into a finished attic, the floor is sheated but it's still an unheated space in winter. The pipe will be laying ontop of the sheating and out the side of the house. Can I use 4" metal vent for this? Should I insulate and if so how? Frame a box around the pipe filled with insulation? Or buy pre insulated vent pipe or flex hose?

Thanks for any advice on this

acerunner · 09-24-2011, 02:37 PM

This is a non critical application. Most pipe will be fine. Flexi, rigid, even vinyl is acceptable here. No need for insulation.

There's really no need to box it up either. But since you say the attic floor is sheathed, i assume you use the attic for storage or something. In which case, you CAN frame it to prevent tripping over it or things falling on it.

Ron6519 · 09-24-2011, 02:50 PM

In your location, you would insulate the ducts. You can buy insulated ducts or you can buy an insulated covering for your ductwork.
If the attic is finished I would route the ductwork so it wasn't on the finished floor.

ponch37300 · 09-24-2011, 04:33 PM

Quote:

Originally Posted by Ron6519

In your location, you would insulate the ducts. You can buy insulated ducts or you can buy an insulated covering for your ductwork.
If the attic is finished I would route the ductwork so it wasn't on the finished floor.

Thanks Ron. Can I use the insulated flex duct for this? The floors of the attic are sheated for storage, not truely "finished". I need to run the vent perpendicular to the floor joists so it's going to have to go on top of the sheating.

Ron6519 · 09-24-2011, 05:07 PM

Quote:

Originally Posted by ponch37300

Thanks Ron. Can I use the insulated flex duct for this? The floors of the attic are sheated for storage, not truely "finished". I need to run the vent perpendicular to the floor joists so it's going to have to go on top of the sheating.

Unless your code restricts it's use, you can. Just minimze the turns and distance to the exterior vent. The fan instructions should let you know the maximum distance the ducts can run. And this is not just linear ft. Every time you make a 90 degree turn, it equals 5 linear feet added to the calculation.