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Old 09-01-2012, 05:54 PM   #1
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Securing furnace exhaust ductwork


Had the opportunity(?) this week to redo the exhaust ductwork in my son and DIL's house. All went resonably well. It's a mid-90's "high efficiency" furnace. For that age I suspect about a 90% efficiency. No PVC. I used 4" double wall, type B I think it's referred to. Question is, can it be secured directly to a 2x4 or is that going to be a fire hazard. The point in question is about 12' into about a 20' run. I felt I needed some support there so I cut a saddle into the end of a 2x4 for the pipe to rest on. Right now the pipe rests directly on the end grain. Is this an issue? What can I use to insulate it if I need to change it?

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Old 09-01-2012, 06:10 PM   #2
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Securing furnace exhaust ductwork


B vent requires 1" of clearance from anything combustible, so resting on a 2X4 is a code violation. If its a 90% efficient furnace, then it isn't permitted to be vented in B vent/double wall pipe. Might want to post the model number an brand.

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Old 09-01-2012, 07:21 PM   #3
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Securing furnace exhaust ductwork


totally agree with beenthere ..90% furnaces are vented with pvc piping...if your 90%furnace is vented with b vent....its wrong period.....
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Old 09-01-2012, 07:54 PM   #4
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Securing furnace exhaust ductwork


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B vent requires 1" of clearance from anything combustible, so resting on a 2X4 is a code violation. If its a 90% efficient furnace, then it isn't permitted to be vented in B vent/double wall pipe. Might want to post the model number an brand.
Rats, I was afraid of that... oh well,, that's why I asked. I haven't got the model number handy, will have to run across town to get it. Will post later.
I assumed B vent was acceptable for that furnace as that's what was there, I just rerouted it because the old masonry chimney was being removed.

Edit - I ran over and looked at it before I hit submit.
Ok, it's a Coleman Evcon. I found the installation sticker. It said for a vertical venting (Category I) I should use type B with 1" clearance so looks like I'm OK in that department.
The issue now is how to support it. I went with a 2x4 because about 4' sticks out into the middle of the attic with nothing close to support it. I've got some of that perforated metal strapping. Hang it from overhead? would be about 4' of strapping to do that. Use the 2x4 with a "cradle" on top made from the metal strapping to hold them apart an inch or so?
Open for suggestions
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Old 09-01-2012, 09:12 PM   #5
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Securing furnace exhaust ductwork


Loop the strap around the vent pipe then secure the strap at both ends.

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Old 09-01-2012, 09:27 PM   #6
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Loop the strap around the vent pipe then secure the strap at both ends.

Thanks for the input. I was getting the same message on my own I guess. I was really wanting to avoid hanging it from the rafters. No real good reason. Suppose will take care of that little detail tommorrow. Thanks again.
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Old 09-01-2012, 10:25 PM   #7
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Yep, metal plumbers strap works real well.
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Old 09-01-2012, 10:33 PM   #8
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Securing furnace exhaust ductwork


Probably not needed but what do you think of a 3 point deal. Attach a strap around the pipe at two points on the ceiling and then another strap attached to the floor? The roofers are gonna be doing that side of the house next week and are gonna need to be bumping the thing around putting on the flashing and roofing around it.
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Old 09-01-2012, 10:38 PM   #9
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Not needed. And will probably cause noise issues down the road due to expansion and contraction of the pipe.
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Old 09-01-2012, 11:01 PM   #10
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Not needed. And will probably cause noise issues down the road due to expansion and contraction of the pipe.
OK, thanks. I guess I'll tie it up tommorrow and just recheck it when the roofers are done. Thanks for the input.

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