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
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.
I suggest that you touch that part of the exhaust
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.
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.
"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
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
_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.
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.
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,
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
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
I left out some information because I wanted some general impressions more
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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