Need advice on bathroom fan vent

[Jakester]

We are remodeling our upstairs bathroom and the old fan has the vent just going into the attic. I replaced the fan with a Panasonic FV-05-11VKL and need to add the proper vent. What is the best option for a vent? Go through the roof or run a 22-25 feet vent to the side of the house?

I am in PA and want to make sure I don't have condensation issues because of hot summers and cold winters.

 

[Gsmith22]

I put mine vertically up and through the roof but that was because I timed the vent install with a new roofing install so I had the roof vent on hand when the roofers were there. It was a direct vertical run of maybe 3 feet. If I had a sidewall closer, I probably would have done that instead as I try to avoid holes that need to be flashed in the roofing plane. Have a roofing replace coming up?

22-25 feet sounds like a long way to run to a side wall. If you do that method, make sure it is well insulated and that you maintain a constant slope toward the exterior wall so that any condensation that can occur drains to the outside. If you use flex duct (besides the obvious friction it creates for flow), it better be well supported so you don't have dips that collect any condensation that does occur.

 

[Sponsor]

 

[Jakester]

What roof vent did you go with? I will need a new roof soon and if I go with the roof vent it will be done at the same time.

I will also need to add a vent for the range hood vent, it is pretty close to the same area of the bathroom vent. Would it be ok to have two vents in the roof close together? Or should I run the range hood vent 20 feet to the side of the house?

 

[Gsmith22]

unfortunately, i moved from that house so I can't go look at it but it was something like this:
https://www.amazon.com/Builders-Best-012633-Galvanized-diameter/dp/B0085KZPCU

I didn't get it from Amazon - i got it at a local plumbing supply. might have been broan - it was probably the same unit as the link with a Broan name on it. My main concern was that I got one with a 6" dia vent because the vent fan that I purchased was 6" dia. And a 6" dia vent was hard to find. I didn't look at your panasonic model so I don't know if this applies to you or not.

If you do have the roofers put it in, I would advise locating the center of where you want it to go through the roof with a nail (after the roofing removal) and then cut out the opening with a jig saw from below (so you can locate between rafters and not have them cut in from above through a rafter). I put the nail through the roof to center it and let them cut it out from above not realizing they would attempt to cut a circle with a sidewider circular saw plunging it into the deck. It worked fine but looked like hell from the attic side (I know who cares/no one sees it).

 

[Gsmith22]

oh, to answer your question about the range hood. It would depend on the diameter of the hood pipe and if a comparable vent piece can be had but I don't see anything inherently wrong with that. Maybe that is 6" too? not sure. I wouldn't place them directly next to each other maybe have at least one rafter bay open between them just so the roofers can properly flash around them. There is probably a building code min distance but I don't know what that is. You can peruse the PA adopted IRC here is you desire: https://codes.iccsafe.org/content/IRC2015 but i didn't see anything in my quick search. Common sense probably rules here over a min distance.

 

[Jakester]

Thanks, my bathroom fan can use a 4" or 6" but since it is only a few feet to the roof 4" will be good enough.

I was wondering about the min distance between two vents if anyone has an answer please share.

 

[Jadziedzic]

If both are "exhaust" vents there is nothing in the IRC that requires a specific spacing. Be sure both vent duct runs have back draft dampers to prevent one of the exhaust vents from acting like an air intake; the IRC (section M1504.3) requires a 3' spacing to "gravity air intake openings, operable windows and doors". As for whether you can vent through the side wall, the installation instructions for the exhaust fan and vent hood should both specify the maximum duct run; if not, there are tables in the IRC you can use.

Don't use any sort of flexible duct for either run; use galvanized metal pipe with all seams taped with metal tape OR sealed with mastic. Insulate the duct with plenty of insulation to minimize condensation issues, and slope any horizontal runs to the outside. I personally would opt for a path through the roof to minimize the duct length.

 

[Jadnashua]

PA in the winter might end up with a lot of snow on the roof. That can be an issue. Mine does go through the roof, but I tend to not use my vent much in the winter. Depending on your house, how tight it is, and the number of people, you probably will want to use yours in the winter. The hot moist air can create an ice dam. Sometimes, it works better to put it on a riser so it's discharging higher, above the typical snowpack, or run it out a sidewall. If you do decide to go out a sidewall, use a larger diameter duct to keep the friction down. The spec sheet for the fan will list the maximum distance, but keep in mind that is the effective length that needs to take into account any elbows.

 

[Jakester]

Last few days I spend a good bit of time running errands and as I was driving around I was looking at houses and just about every house has their vents in the soffits including houses that have been built within the last few years. My soffit is only 4.5" and there is no way I could get a vent there anyways.

For whatever reason I really want to avoid adding any vents through the roof.

 

[Gsmith22]

prior to putting the vents in my roof, both upstairs bath fans were vented to the soffit. Sounds great on paper. Doesn't work. most roofs/attics are vented were air is brought in the soffit and exhausted at the ridge (or gable vents). So you would be trying to exhaust air from the bath fan out into an incoming air stream. Both of my upstairs bath fans were vented this way and when the roofing was replaced, all the sheathing just upslope of those two soffit vents was rotted and had to come out. Exhaust from the bath fans with humidity was brought back into the attic and pulled across underside of sheathing rotting it over time.

 

[Jakester]

And this is what I don't understand why they still build houses with vents going out the soffit at least in our area they do.

 

[Gsmith22]

people do and build lots of things they shouldn't. "good practice" and "it exists" aren't the same thing

 

[Jakester]

So you guys think that running 4" rigid pipe with insulation 25 feet is a bad idea?

 

[Jadziedzic]

The longer the duct run the more chance for the heated humid air to condense; insulation helps, but it's still likely you'll have condensation in the vent near the exit if you run the vent 25 feet. If you insist on that long a run, be sure the pipe has a downward pitch toward the exit, keep the length-wise seam of the duct facing upward, and have the corrugated (narrower) ends of the duct facing toward the exit path so any condensation makes its way outside. And insulate the heck out of the duct. I've never done so, but I wonder if using 4" PVC DWV pipe for the exhaust duct might work; fewer joints, although you'll possibly have issues with lengthwise expansion and contraction of the PVC pipe.

FWIW, I have a Broan roof-mounted cap on my house here in New Hampshire, with about five feet worth of duct from the vent fan and a double layer of insulation. Even when we had a foot+ of snow on the roof the exhaust was warm enough to melt the snow over the roof cap by the end of the first shower.

 

[Jakester]

I was thinking about 4" PVC DWV pipe as well. Is it ok to do that? How would you connect it to the termination vent on the wall?

 

[Jadnashua]

Check out the specs on the fan in question. They all have a chart in there that tells how long the effective length of the duct can be. It probably will want the duct to be 6" to allow it to flow the designed air volume. I wouldn't use pvc...in an attic, the heat will cause it to warp.

Effective length is the sum of all straight sections plus a factor for any elbows.

 

[Jakester]

I read through all of the specs and instructions of this model and it doesn't say anything about minimum or maximum pipe length.

 

[ImOld]

I looked at the install directions. No mention of duct length but it does say the flow rate is adjustable. Crank it up and you should be good to go. I would never go out the side but maybe you don't like climbing on roofs. Heed the advice about side of house exhaust. Insulated duct is readily available at the big boxes. Use it and stop all this crazy talk about pipes.

 

[Jakester]

I looked at the install directions. No mention of duct length but it does say the flow rate is adjustable. Crank it up and you should be good to go. I would never go out the side but maybe you don't like climbing on roofs. Heed the advice about side of house exhaust. Insulated duct is readily available at the big boxes. Use it and stop all this crazy talk about pipes.

Why wouldn't you go out the side?

 

[ImOld]

Siding, like roof shingles, are meant to have whatever flow downwards without penetration. Roof overhang/soffit from above. If you now have clouds of moisture coming from below, you will have penetration. If your house has a house wrap, the moisture can be trapped between the wrap and the siding. I have removed good looking siding where the sheathing underneath was rotted away from moisture penetration. I'm sure it took a year or two. If you let the fan run for awhile after bathroom use it should clear any moisture out of that long run. I'm 82 years old and love to run around on roofs!