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Old 09-07-2010, 04:32 PM   #1
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duct wrap plus add'l insulation - too much of a good thing?


hi all - just read thru a bunch of posts on bath exhaust here. thanks in advance to all the folks who always offer great advice here. I'd appreciate some thoughts on this install.

I'm running a new bath fan 70 cfm with 4" duct. All pipe is the 30 gauge galvanized. There's 2 bends right at the fan. Just off the fan the 1st elbow connects and turns upward @ 45 deg. Then a very short piece of pipe to the second elbow which turns back 45 deg again to horizontal. This first run is enough to clear the joists + the existing insulation (roxul batts) and also give me a couple inches of play so I can slope the rest of the horizontal run towards the gable end. I set the elbows to 45 and 45 instead of 90 and 90 thinking it would be a bit better for airflow - does that really make any difference or was it overkill? Just curious at this point since I got them up there now. Anyway, from there I go about 15' with one more 90 deg bend that takes me to a gable vent. I wrapped the entire horizontal run (approx 17' overall) with reflectix duct wrap and taped the seams.

I'm assuming the 70 cfm thru this run going to be sufficient - bathroom is @ 8 x 8 x 8. I don't mind running the fan for longer if need be. My main worry is condensation - I think I read here some differing opinions on further burying the duct. I was thinking of getting a couple bags of loose insulation and covering over the duct completely in addition to the wrap. Would I be better off leaving it alone with just the reflectix wrapped around it (wrapped and taped from end to end)? I want to overkill this now but I also don't want create another worse problem.

thanks

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Old 09-07-2010, 05:35 PM   #2
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duct wrap plus add'l insulation - too much of a good thing?


Wrap anothe rlayer of reflextic around it if you want.

A 45° is equivalent to about 5 foot of duct length. A 90 is equal to 10 foot. So you did help your fan.

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Old 09-07-2010, 07:44 PM   #3
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duct wrap plus add'l insulation - too much of a good thing?


Sounds like you may be North of me.... to fight the cold: http://homes.winnipegfreepress.com/i...article&id=702 Use a damper door on the termination hood to keep the cold air out of the ducting.
Insulate the fan box.

Gary
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Old 09-07-2010, 08:23 PM   #4
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duct wrap plus add'l insulation - too much of a good thing?


beenthere - thanks for the sanity check. Always good as a DIY to find out I did something right . And for an extra $20 or so I just might wrap it one more time if that helps.

GBR - I'm in Northern Ontario Canada - the place I'm working on is my camp off the shore of Lake Superior. It can get pretty chilly up here (probably not as cold as Winninpeg though - thanks for the article). I would love to spray foam this whole run but I think that might be a lot of cans. Interesting how they talk about not using the fan as a potential problem. I might take the leftover pieces of the reflectix and button down the outside of the fan housing. I have a couple of extra batts I can lay overtop the unit too. It's that run of pipe that I worry about.

The hood I have is just a basic unit from the lumber yard - with the 3 louvers / flaps on it (I have one on my dryer vent at home and it's held up well over the years) with a critter hood / screen over top. I saw one of those Broan eco-vents a the big box http://www.homedepot.ca/catalog/hood-vents/173091
and it looked real interesting - but I also read some reviews and stories like this one http://hvac-talk.com/vbb/showthread.php?t=158705 about them freezing shut in the extreme cold (not so much on dryer vents but mostly on bathroom vents). This hood is easy to change at this point if you guys recommend something in particular...?

thanks for the feedback.
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Old 09-09-2010, 09:22 PM   #5
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duct wrap plus add'l insulation - too much of a good thing?


On this site, the louvered door is a type"A" dryer hood: http://www.appliance411.com/faq/dryer-vent-length.shtml
Compare the manu. run listings---- 50% more for the type "A" over "B". I found the wet lint collects and drys on the louvers, keeping them open and sticking. Unfamiliar with the Broan bath hood, perhaps Beenthere is?

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Old 09-10-2010, 03:10 AM   #6
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duct wrap plus add'l insulation - too much of a good thing?


Quote:
Unfamiliar with the Broan bath hood, perhaps Beenthere is?
Afraid I'm not.
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Old 09-10-2010, 02:23 PM   #7
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duct wrap plus add'l insulation - too much of a good thing?


no worries guys i appreciate your feedback. maybe the Broan thing is more unique to Canada and the deep freeze winters we get. Looks like a great concept and I would maybe take a chance on one if the vent was closer to ground level but the prospect of climbing the ladder up to the gable end in -25 deg winds to free up a stuck vent is not too appealing .

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