Protecting PEX from heat

In my house I have a run of PEX tubing that runs right past, almost touching in fact, the gas vent for the hot water heater. My concern is that the PEX is in danger or melting or accelerated decay due to the heat. Is there some way I can shield the PEX from the gas pipe, would there be a code or fire reason why this particular section needs to be rerouted away from the exhaust pipe?
Just to clarify the exhaust from the water heater would have traveled about 5 feet before reaching the point where it is near the PEX so I presume it would have cooled down some.
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Eigenvector wrote:

while the water heater is firing to see whether it really is hot.
To answer your question, you if you put a piece of thin aluminum like flashing between the exhaust pipe and the PEX with just 1/8 to 1/4 inch space between pipe and aluminum and between aluminum and PEX that would end your heat problem. If you don't have that much room, you could take aluminum foil crush it (do not make neat folds) and place that barrier between the pipe and the PEX. Chances are essentially no heat would transfer to the PEX. The real question is whether this is PEX for hot water or PEX for cold water, since since tubing for hot water needs to be designed for at least 140 degrees and the exhaust pipe not even be that high in temperature.
Of course, the real solution, if the exhaust pipe actually gets hot, is to cut the PEX and insert a short fitting to gain room. That would be about $2 for the fitting and $6 for several steel bands and $10 to rent the crimp tool for 2-4 hours.
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1. You could use copper pipe instead. 2. You could insulate the pex with something that is OK if it touches the exhaust vent.
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I would get a piece of plastic automotive grade wire loom and put it around the PEX or just get some of that round flam insulation intended for hot water copper tubing that is available at any DIY place. It's like $1 for a 6 foot length.
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to protect the PEX just in case.
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"flam"? Was that a typo? Normal foam pipe insulation isn't heat proof by any stretch. There are fiberglass pipe insulations that'd work, but these are harder to find.
Or secure a wad of fiberglass, or better still, rock wool in betwixt.
[I wouldn't recommend a metallic foil, because there's a good chance it would flatten out over time, and the end result would be worse (metal conducts heat better than air) than what you have now.]
Building code requires a 1" airgap or insulating material (usually a wad of fiberglass) between romex and hot air ducts. This is not just an heat issue, but a vibration one. A vibrating duct will eventually wear through romex sheath if they're in contact.
Here we're talking about an exhaust duct, and the temperatures are bound to be higher than a hot air duct. (though, with a high efficiency unit, the temperatures would be about the same)
Building code talks about permissible gaps between flues and flammable materials. PEX is likely flammable for code purposes (wire insulation almost always is).
It may be worth a visit to the library to read a copy of the local building code to see what it says. A house inspector would probably know, and if so, could certainly tell you what local "good practise" is. A building code inspector certainly would.
Apropos this - one of my SILs recently bought a house. The first piece of flue from her mid-efficiency furnace is a 2"-ish pipe encased in a 3" diameter shell. This connects directly to the outlet of the exhaust blower.
Aside from vibration abrasion, this probably wouldn't be an issue if in contact with building wire or a plastic pipe.
_However_, the inner flue only "engages" the blower housing with _less_ than 1/8" of tubing overlap! It's not otherwise physically connected. One slight inadvertant knock, the pipe pops off the blower without it being visible, and the furnace is venting directly into the basement.
Yow!
A mandatory must-fix ASAP.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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Ultimately I think I'll just reroute it anyway, but for the time being I wanted a way to prevent it melting and bursting. It isn't touching the pipe, but it certainly is close. I'll take a look at the codes and see what they have to say then insulate the PEX with something non-flamable, non-metalic.
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I was implying that with my #2, since I believe that there exists insulation materials available that would be OK touching the vent. Obviously, I have no idea if there is enough clearance all the way around the pipe for an insulating piece (which should be pretty easy to install).
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On Wed, 12 Jul 2006 20:12:52 -0700, "Eigenvector"

If this was my house I'd spend $20 or so to get that PEX away from that exhaust vent. Why risk your home and life for $20. ANYTHING flammabe should NOT be near an exhaust pipe from a gas heater. PEX is some type of plastic. Plastic burns/melts. If it dont actually ignite, it could melt and cause a flood. Reroute it and feel safe. If there is stuff in the way, you could use galv, steel pipe or copper pipe from the heater to a foot past the vent pipe. Use the PEX beyond there.
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In spite of all the concern, it is really? If the gas vent is a PVC vent, it would not be ea problem as there is so little heat. We really need better information.
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wrote:

than anything. Yes it's a 3" galvanized exhaust pipe leading to the roof for the water heater, the PEX as it stands is already about 2 inches away from the pipe, but as it is a temporary fix it is relatively unsecured so it may flop around a little bit as the PEX expands (which by the way is a disturbingly large amount). It will never come within 1 inch of the exhaust pipe however much it expands.
I agree with the Souperman dude, it should be rerouted and it will when the rest of the pipe section is replaced.
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