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Old 11-26-2012, 12:26 AM   #1
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Duct Trunk Alternatives


I suppose it's possible I'm crazy, but is there a good reason not to use plastic for main trunks on my forced air furnace? My initial concerns were off gassing, mold, and static electrity. From what I'm reading, HDPE doesn't have the off gassing problems of polypropylene, doesn't have mildew problems (plus, I don't have air conditioning anyway), and I'm totally unsure of whether static electricity would be a problem.

I've seen the foil-faced cardboard panels for return air and was thinking the same type of thing should work for hot air. Initially I thought corrugated HDPE would be best as it would insulate as well, but I'm not sure if that would be worth the price compared to regular HDPE panels. EIther should install easily and may be a lot cheaper than metal.

So, any thoughts?

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Old 11-26-2012, 07:25 AM   #2
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Insulated flexable ductwork is made for cooling and heating.

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Old 11-26-2012, 09:19 AM   #3
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Originally Posted by COLDIRON
Insulated flexable ductwork is made for cooling and heating.
Yes, but doesn't flow as well. And it's not very easy to run stubs off of.
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Old 11-26-2012, 09:41 AM   #4
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Yes, but doesn't flow as well. And it's not very easy to run stubs off of.
You're not supposed to run take offs from flex duct. Y's, yes. Take off's, no. You can always use round metal duct and insulate the exterior with insulation if you're wanting low air flow resistance. In general when switching from round metal to flex you upsize the flex one size to accomodate for resistance.

Plastic is a fire hazard.
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Old 11-26-2012, 07:57 PM   #5
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Duct Trunk Alternatives


Quote:
Originally Posted by Doc Holliday

You're not supposed to run take offs from flex duct. Y's, yes. Take off's, no. You can always use round metal duct and insulate the exterior with insulation if you're wanting low air flow resistance. In general when switching from round metal to flex you upsize the flex one size to accomodate for resistance.

Plastic is a fire hazard.
Thank you, but still not all I'm looking for. My goal is to get a large trunk run and use the solid metal round duct I have or take offs. So, I won't be using any of the insulated round flex duct.

How is plastic a fire hazard? It melts at 162, far above the 110 coming out of the furnace. How is the flexible not the same hazard?
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Old 11-26-2012, 09:13 PM   #6
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http://plasticsupply.net/Ducting.html

http://www.harrisonplastic.com/ductwork.html

Check those sites out.
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Old 11-27-2012, 01:40 AM   #7
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That's the first I've ever heard of plastic duct.
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Old 11-27-2012, 05:10 AM   #8
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That's the first I've ever heard of plastic duct.
Used in corrosive environments. I've seen it maybe a handful of times.
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Old 11-27-2012, 07:05 AM   #9
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I never heard of it either and I have done work in several labs.
I'll bet that stuff costs an arm and a leg.
Sounds like overkill for a residential home.
I would run regular galvanized main trunk line and have flex takeoffs to the diffusers. Then insulate the main.
OH ! That's for an attic installation, if it's ground floor or basement feeding up I would use galvanized main trunk with regular galvanized pipe to the diffusers.

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