Location of bathroom exhaust vent
Just a quick question. I live in climate zone 4A in Virginia, and will have a vented attic. I want to minimize the penetrations in my roof, which leaves only two choices for locating my bathroom exhaust vent:
1) Straight out the bathroom’s exterior wall (about 5 feet from the fan), and venting outside one foot below the soffit (I’ll have a raised heel truss), with the moist air directed down.
2) Having the vent pipe going up into the attic, and then horizontally 15 feet away to exit in the gable.
I want to avoid having moist air rising into the attic through the soffit, but wonder if keeping the vent a foot below and venting downward would reduce that issue.
I’m not fond of the thought of a long vent pipe carrying warm, moist air traveling at least 15 feet in the winter cold. Even with insulating the vent pipe, I’m concerned about condensation.
Any thoughts or suggestions? Thanks.
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Replies
I'd do the 15 foot run. Make it angle slightly downward towards the gable so any condensation can run out, and make sure the vent allows for that.
Charlie, can you explain "make sure the vent allows for that"?
I just meant that if there's a spot water can pool rather than run out at the vent, that isn't ideal. If you get it and look at it and think about what happens if water runs down towards it, ideally there would be a path for it to go out before it backs up.
Debra,
You have a vented attic, so doesn’t option (1) also involve a duct run through the attic?
I am also debating these options for my project. I hope your question receives more attention. Good luck!
Aaron
Aaron, the 5-foot duct to the nearest wall could be placed underneath the attic insulation. Running the ductwork 15 feet away, sloping down, would require the duct be above the insulation.
I know from experience that in terms of moisture removal, in the shower works much better than outside the shower.
I’d run the vent out through the gable wall. Just insulate the duct run, and pitch it slightly towards the exterior vent. You shouldn’t have any problems, this is a common application. If you go out through the bathroom wall, you’re likely to introduce a lot of humid air to your attic through the soffit vents which is something you should avoid.
Bill
I had the same problem and opted for a wall-mounted Panasonic fan. Utter simplicity, and quiet, too.
Joel,
Was it a whisper wall fan?
yes. I am surprised how little air backdrafts through it.
Peter's comment below is that some of them aren't very air-tight, but they sure seem like a good solution to a question that gets asked over and over.
Hi Debra -
Through-the-wall exhaust fans are really energy and air-leaky. Tamarack Technologies used to make a through-the-wall that was insulated and gasketed with motorized damper that really worked well, but it was too expensive, they did not sell enough of them, so they dropped it.
So in my bathroom, I ran a high-efficiency exhaust fan from Tamarack (https://www.tamtech.com/product/100-cfm-in-line-ducted-bathroom-fan-kit/), including a butter-fly backdraft damper inline in the 4-inch metal duct (looks like Tamarack no longer makes these in 4-inch but I have also used their Cape flexible dampers and they work great), which I buried in attic insulation and ran out the gable, pitching slightly down to the exterior to drain any condensate.
Thanks, Peter.
We did option 1 with a Panasonic Whisper Green in our house and I think it was a good simple solution...as it avoids having to run a duct into the attic (and the 20"+ of cellulose on the attic floor). We built a small chase or compartment out of 2x4s and pine boards, a photo is attached.
Brian, yes, I've also considered creating a dropped soffit in the bathroom to run ductwork to the nearest wall. This would keep the duct in conditioned space and avoid creating another penetration in the ceiling air barrier. But that could still introduce humid air in the my soffit above. Guess I'll go the gable route.
The Panasonic I used is model #fv-08wq1 which is a wall mounted unit - no duct at all.