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.
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Replies
Randy,
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.
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...
Randy,
If you want a classy stainless-steel termination for your duct, you could spring for one of these pricy units from Seiho:
http://www.seiho.com/product/rcarcc/rcarcc.html
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: http://www.seiho.com/product/index.html
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?