Confused!! Should we vent bath fan through roof, soffit, gable end?

[staceyneilcollins]

Our house is built of thick masonry block. NOT fun to drill through! It's a one-story ranch in Maine, so we have cold snowy winters and humid summers.

We need to replace a bathroom exhaust fan before we have blown-in insulation installed in the attic this winter. Here are our choices... given our location and parameters below, which do you guys think is best?

1) Through the roof. It would be about a 10' run of pipe and would have to cant at about a 45 degree angle (ie not straight up) to place the roof cap on the back side of the ridge where it wont be horribly obvious. We already have a veritable forest of roof protrusions back there: range hood fan, two plumbing vents, wood stove chimney, and solatube dome.

2) Through the soffit. Exterior wall is only 3' away from fan location and eaves are more than 12" wide. But I have heard this is not a great solution re: moisture re-entering attic.

3) Through the gable end wall of the attic (which is wood, not masonry). This however is a ~19' run of pipe.

If you can also advise what type ducting to use, that would be great. If it's # 2 or #3 and is buried under a foot of blown-in insulation, do we need to use insulated pipe? Where does on buy insulated pipe anyway?

Thank you so much!!!

[jadnashua]

First thing to check is the specs for the fan you want to use...it may have a limitation on how long the ductwork can be. Any good hvac place will have insulated round ductwork. If you can use Grainger, you can buy it from them as well. I use my vent during the summer, and not all that often in the winter, since I normally run the humdifier, so just opening the door means less the humidifer has to deal with. But, given it is on the roof, if there is a lot of snow, depending on the type of roof cap you use, it might be underneath, especially in Maine. It might be easier to run it to the gable end wall, but the length might be a problem. You don't want it to condense and then drip back into the bathroom. Hot, humid air will probably rise enough if you went through the roof to minimize that. If you had the run to the gable end rise all along the way, that would help the airflow as well. Dumping it into the soffit might work, but assuming you have vents there for airflow into the attic, you don't really want to dump all that moisture there.

See what other thoughts you get.

[Ian Gills]

I'd go through the gable end. My neighbor did that (although he had a shorter run). Cutting though wood and then siding appeared to be very easy, which is an important consideration.

[frenchie]

Venting out the soffit's a good way to rot out your roof.

Either of the other 2 work, although that does seem an awfully long run to the gable.

I'd go up & out the roof.

[staceyneilcollins]

Thanks folks!

So it seems like we're down to either the gable end with a long run, or through the roof.

Roof is only a 5:12 pitch, but we could put the cap near the ridge.. which hopefully would minimize snow, right? Seems snow's the only detraction from that plan. And I guess unlike a dryer vent or range hood exhaust, the air temp from a bath fan is not necessarily hot enough to melt snow.... hmmmmm.....

Anyone else want to chime in?

[jadnashua]

There are all sorts of roof jacks for that exhaust. You could run it up a ways so snow shouldn't be a problem. It is imperative to have a good damper on it, though.

[Iree]

What is shortest distance to the nearest exterior wall. I just did two - one through the roof and one though the side of the house.