Helpful? 0

Bath fan ductwork - material and insulation (revisited) -

First, apologies if this should be under the "general questions" category

I saw some information from Riversong in response to a bath fan duct question asked quite a while ago (posted by Chris Johnston - Thu, 08/26/2010 - 14:57). The essence of the response was that plastic duct (glued, sloped) was somewhat insulative, and condensation would drip out (sloped out to vent cap) via the 1/4" per foot slope.

Still dealing with (what I hope is) the tail end of the coldest winter in probably 30 years here, so the 'insulative" thing kind of peaked my interest. I hope I can ask for a sanity check on this almost 4 years later - is this still the Riversong (or collective GBA) wisdom?

Reason I ask is that I just 'fixed" my smooth metal bath exhaust ductwork (I admit I botched the slope and got some water dripping into the house in Feb). In the repair process, I decided to replace it with light PVC with glued joints (to make it watertight end to end) and sloped to the gable wall, and I also pulled a light insulation sleeve over it (box store stuff @ R4 or R5 best case) . I keep wondering it that is enough insulation for the cold Canadian winters, like this year (ouch) as I haven't had a chance to let it "soak" yet (pardon the pun - next winter will tell, I suppose) but I'd like to get this project finished with some confidence now. For me, a few drips == a huge worry.

FWIW I read about the "reversed Riversong truss" concept here a while ago, while doing the retrofit on my kitchen ceiling last year - and stole the idea. Excellent - so now I gotta respect the advice here even more. Thank you.

Asked by Randy Toni
Posted Thu, 03/13/2014 - 16:00
Edited Thu, 03/13/2014 - 16:04


5 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Helpful? 0

It sounds like your bath exhaust duct installation is better than 95% of existing bath exhausts. It sounds like a good job.

Just make sure that the duct is supported with plenty of hangers or loops of perforated strapping, so that the duct maintains its slope and doesn't sag.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 03/13/2014 - 16:22

Helpful? 0

Martin - thank you for the very quick response. Much appreciated. Do you recommend a particular vent hood (the louvered one I have, also box store) seems to freeze up on the really nasty days, and is pretty flimsy. I might also replace this since I'm into this work, and now transitioning to PVC at the wall. Thanks again...

Answered by Randy Toni
Posted Thu, 03/13/2014 - 16:39
Edited Thu, 03/13/2014 - 16:48.

Helpful? 0

If you want a classy stainless-steel termination for your duct, you could spring for one of these pricy units from Seiho:

Answered by Martin Holladay, GBA Advisor
Posted Thu, 03/13/2014 - 16:52

Helpful? 0

The Seiho vents are great and actually not that expensive in my opinion. I just got mine for my dryer duct and love it. They make several different models besides the one Martin linked:

Answered by Nick Welch
Posted Thu, 03/13/2014 - 17:22
Edited Thu, 03/13/2014 - 17:23.

Helpful? 0

Thanks Martin / Nick - those units are certainly a cut above the stuff I've been using. I'm now leaning towards a unit with no backdraft damper as this would mean a bit less static pressure in the run, and taking into account the fact that the fan has a damper in the duct connection, plus I'm a bit gun-shy after seeing my current cap (albeit a cheap one) freeze up. And my fan is only 80CFM (small bathroom, @ 60 sq ft) so I think I'm on the fringe of good airflow with the run I have now. We get some wild winds where I am but this is a leeward wall, so I might get away with it. Any thoughts?

Answered by Randy Toni
Posted Fri, 03/14/2014 - 13:32
Edited Fri, 03/14/2014 - 13:34.

Other Questions in Green building techniques

In General questions | Asked by Jin Kazama | Aug 28, 14
In General questions | Asked by Steve Young | Aug 16, 14
In Plans Review | Asked by Nick Campbell | Aug 26, 14
In General questions | Asked by Jacob Roark | Aug 28, 14
In Mechanicals | Asked by austin jamison | Aug 28, 14
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!