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How close can exhaust furnace pipe be from gas ln


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Nothing should be in contact with the flue pipe. As for being safe, unless that pipe gets hot enough to ignite the gas inside the pipe you have nothing to worry about. The chance for that happening are about as good as getting hit by a meteorite.

Fuel only ignites in the presence of the proper concentration of oxygen. Too much or too little and it will not ignite. A sealed gas pipe should have no oxygen. Regardless of how hot it gets, it should not combust... unless oxygen at the proper concentration is available inside the pipe.

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Nope. I've had folks whose opinions I respect insist they get really hot, but I've not seen it.

As long as the furnace is working properly, the outside of the

B-vent is never going to get very hot. But when things go wrong, the temperature can really take off.

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I have never seen a B vent causing any signs of overheating a surface no matter what it is touching. Does someone have a picture?

I've posted some in the past. They show burned vinyl on insulation near the B-vent just above the furnace. Right now, I'm in Connecticut and I don't have access to my archive. If I remember, I'll post them when I get back next week.

I've never seen or heard of heat from a B-vent damaging the paper on drywall, charring wood, or anything like that.

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I have never seen a B vent causing any signs of overheating a surface no matter what it is touching. Does someone have a picture?

I happened to snap this pic today, a note from the authority to the flunky?

Click to Enlarge
tn_2014101003715_Dscn4588.jpg

44.36 KB

No, it is not what you asked for, but it has relevance, I thought. [:)]

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I have never seen a B vent causing any signs of overheating a surface no matter what it is touching. Does someone have a picture?

I happened to snap this pic today, a note from the authority to the flunky?

Click to Enlarge
tn_2014101003715_Dscn4588.jpg

44.36 KB

No, it is not what you asked for, but it has relevance, I thought. [:)]

Jeeez, that's nothing! My morning breath can melt plastic [:-yuck]

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The wall firestop in the pic appears to be laid over plastic. Therefore, one cannot ascertain if it is encroaching on stated clearances or not. A firestop must be framed in on four sides with an inner and outer listed firestop. If this is scrap sheetmetal, it would fail but I think I see the rivets for the spacers. Still, I'd call for a pro to remove and inspect it. Often well meaning people will pack insulation into firestops which is a major fire hazard.

Yes, the surface temps. on much B-vent run so cool it won't char ordinary combustibles or even melt plastic. The 1" clearance factors in for an abnormal overfire condition to provide for some margin for error. Note that most FVIR water heaters exhaust temps exceed 600F, which exceeds the design limit of B-vent at 540F. All vent and vent connectors must be properly supported. This means support in two intersecting planes at all offsets plus a vertical support for any sections going through the roof or every 10 vertical feet. You must use the listed base support too.

HTH

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I have never seen a B vent causing any signs of overheating a surface no matter what it is touching. Does someone have a picture?

I've posted some in the past. They show burned vinyl on insulation near the B-vent just above the furnace. Right now, I'm in Connecticut and I don't have access to my archive. If I remember, I'll post them when I get back next week.

I've never seen or heard of heat from a B-vent damaging the paper on drywall, charring wood, or anything like that.

I've posted these before, but here they are again.

Click to Enlarge
tn_2014101215233_Warm_B_Vent%20(1).jpg

28.13 KB

Click to Enlarge
tn_20141012152318_Warm_B_Vent%20(2).jpg

25.33 KB

Click to Enlarge
tn_20141012152333_Warm_B_Vent%20(3).jpg

24.72 KB

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