Installing bath exhaust fan

[MiamiCuse]

I am installing two Panasonic bath exhaust fans - one FV-08VQ3 and one FV-11VQ3.

Because of the difference in size and location of the new fan, I have to extend the existing 4" sheet metal conduit to the new fan. They are about

30" apart. Should I use new sheet metal conduit to bridge this 30" or should I use a "coiled" looking flex conduit? or PVC pipes?

I need to cut the existing sheet metal pipe back a bit, what is the best way to do this? The attic space is tight I am pretty much limited to hand tools.

Also, I traced the conduit and found that all the bath exhaust conduit do not exit the roof, but simply extended to the roof overhang and sat on top of soffit openings. Is that ok? When the fan is on and moist air is drawn, part of it will exit the soffit vent, but part of it will go inside the attic. Is this acceptable?

Thanks,

MC

[trader4]

The flex pipe is widely used for these applications because it's easy to work with. That's what I would use.

Tin snips.

No, the fan vent should have a direct exit. If it's just laid on top of the soffit, as you pointed out, a considerable amount, maybe even most of the air, is going to go back into the attic. Plus, the soffit area is going to be cold, perfect for condensation to occur. Probably much less of an issue in Maimi than northern climates, but I'd still do it right. Plus, I would expect your code would require it to be properly vented.

[Mikepier]

It's one of those things that's not right, but its done all the time. At least you pointed it out of a soffit. Most people just empty it into the attic. What I did is use rigid duct and ended it right by my attic fan on top of the roof which is already open. At least it goes right up outside. I really did not feel like putting a hole in my roof.

[Joseph Meehan]

When possible use the solid. The flex stuff will reduce air flow. It is harder to install sometimes, but better once in place.

[Joe]

Flex saves a lot of hassles at the cost of slightly less efficiency.

Sheet metal pros use double cut aviation snips. Wiss is a good brand. If all you need to trim is an inch or so, then conventional aviation snips are OK.

No.

Joe

[Joseph Meehan]

I don't see the response I wrote to this question so here it is again, along with some additional comments.

When possible use the solid. The flex stuff will reduce air flow. It is harder to install sometimes, but better once in place.

See the other Joe's answer, it is 100% correct.

NO NO NO! It is often done that way, but it is a very very bad idea. To protect your home you want to get that warm moist air out of it not just move it into the attic where it may cause bigger problems.

[nmbexcuse]

well I have four bathrooms that are "vented" this way via the soffit. I don't want to punch 4 holes in my roof.

One possible solution would be to cut a 4" hole in my soffit overhand (I have a 5' eave overhang all the way around the house with T-111 plywood soffit), so I cut 4" holes in the T-111, then terminate the exhaust pipe with a 90" elbow (somehow) facing down and exit via the soffit. No air will go back into the attic but the moist air will be forced downward. I assume I need some lip/cover to prevent backflow or critters from getting into it.

But since my 4" lines are all currently directing to a soffit vent, if I cut a 4" hole, I need to cut it along the current path and then cut it short to install the elbow. I wonder if I realistically can cut and install a 4" sheet metal pipe and put in a 4" elbow from outside a

4" hole...seems it would be tricky. I don't think there would be a problem were it sheetrock but it's T-111 ply.

This seems to be the only possible solution I can think of now that does not involve a very expensive and intrusive remedy. Any other thoughts would be greatly appreciated.

[Joe]

Your plan seems doable (excuse buzzword). Using a 4 1/4" hole saw on the soffit would leave wiggle room enough for a length of pipe with attached elbow to be threaded into the attic space. Pop rivets attaching the elbow would be tidier and make installation easier. HTH

Joe

[MiamiCuse]

Your plan seems doable (excuse buzzword). Using a 4 1/4" hole saw on the soffit would leave wiggle room enough for a length of pipe with attached elbow to be threaded into the attic space. Pop rivets attaching the elbow would be tidier and make installation easier. HTH

Joe

Yes it definitely help. I think still will be tricky on be on a ladder on the outside (I already crawled from the attic on the inside and no luck reaching that tight space) cut a hole and be able to cut the pipe back and put in an elbow the same size as the hole and doing all that with one hand inside the hole.

I will try to free the pipe from any straps and fasteners to the existing joists...it will be tricky, and probably the solution to each of the four bath will be different.

Thanks,

MC

[MiamiCuse]

Sheet metal pros use double cut aviation snips. Wiss is a good brand. If all you need to trim is an inch or so, then conventional aviation snips are OK.

Thanks Joe. Is this one I can use:

Thanks,

MC

[Joe]

That's the one in my tool box. It helps to drill a 1/4" hole to start the cut with the center blade. On soft thin aluminum the center blade can sometimes be forced into the work to start the cut. Double cuts must never be used for close trimming or edge cuts. Their special use is on sheet metal with a good bit of material on both sides of the outer blades. They are the only way to get clean cuts away from the ends of vent pipe. Have fun.

Joe