PEX onto water heaters

[msteger]

I recall that where PEX (or other plastic pipe) connects to water heaters, that copper stubs are to be used between the two (pipe and water heater)? Is this due to temperature or what? I noticed a 2000 home yesterday had no copper stubs.

[hausdok]

Hi,

I've never heard or read anything that restricted connectors between PEX and a water heater to copper. The only restriction is that you can't connect it directly to the top of a gas water heater because of the temperatures associated with the flue. That restriction doesn't apply to electric water heaters.

ONE TEAM - ONE FIGHT!!!

Mike

[msteger]

That may be what I was thinking, Mike. So it only has to do exhaust gas temps near the plumbing. What if the gas water heater has a power vent and no metal flue vent?

[Jim Katen]

I recall that where PEX (or other plastic pipe) connects to water heaters, that copper stubs are to be used between the two (pipe and water heater)? Is this due to temperature or what? I noticed a 2000 home yesterday had no copper stubs.

I found this in the 2006 PEX Design Guide:

PEX tubing may be connected directly to residential electric water heaters, if the local code and manufacturer’s instructions allow.

But then I found this in the UPC:

604.11.2 PEX tubing shall not be installed within the first 18" of piping connected to a water heater.

I can't find any corresponding reference in the IRC.

- Jim Katen, Oregon

[msteger]

Thanks Jim. Being in PA, we're under the IRC, so I guess this installation is OK then.

So, does that also mean that the IRC also allows this type of install even with a metal vent pipe adjacent to the PEX (similar to what Mike mentioned)?

[Jim Katen]

Thanks Jim. Being in PA, we're under the IRC, so I guess this installation is OK then.

So, does that also mean that the IRC also allows this type of install even with a metal vent pipe adjacent to the PEX (similar to what Mike mentioned)?

The IRC is silent on the issue.

The design guide says:

When connecting PEX tube to gas water heaters, the tube must be kept at least 6 inches away from the exhaust vent of the heater.

- Jim Katen, Oregon

[hausdok]

No,

Manufacturer's specs will trump code and manufacturers don't want PEX near an exhaust vent on a gas water heater. Don't know the answer re. the power vent; I recommend calling the manufacturer.

My gut says that it would be OK cuz those have an interlock on them to shut them down if the blower stops functioning. The interlock accomplishes two things; it primarily prevents the occupants from getting gassed but it also prevents damage to that fan motor from excess heat, so it would make sense that one wouldn't see the temps there that one sees with a conventional tank with flue pipe and draft diverter.

OT - OF!!!

M.

[KGarten]

Actually the IRC does have something on it. G2427.7.7 Clearances (in the fuel gas section) and the appropriate table. If I remember correctly, type b vents are going to allow 1" clearance to combustibles. Single wall will be the 6" clearance.

Defining pex as combustible is where it gets fun. You have to go to ASTM standard E 136 to get that. The short version is anything put in a 750 degree centigrade test that does not burst into flame in the first 30 second or lose more than half it's mass in 30 minutes is considered noncombustible. I think pex would fail the second of those tests.

My opinion would be direct vent would be fine, 1" from type b vents and 6" from single wall vents (so probably inappropriate).

[Brandon Whitmore]

Actually the IRC does have something on it. G2427.7.7 Clearances (in the fuel gas section) and the appropriate table. If I remember correctly, type b vents are going to allow 1" clearance to combustibles. Single wall will be the 6" clearance.

Defining pex as combustible is where it gets fun. You have to go to ASTM standard E 136 to get that. The short version is anything put in a 750 degree centigrade test that does not burst into flame in the first 30 second or lose more than half it's mass in 30 minutes is considered noncombustible. I think pex would fail the second of those tests.

My opinion would be direct vent would be fine, 1" from type b vents and 6" from single wall vents (so probably inappropriate).

KGarten:

Where does the draft hood opening come into play on a non- direct vent? Whether or not double walled connectors/ vents are used, there is that opening that will not insulate/ protect the pipe from the heat.

[Les]

Why does the title of this thread bug me? PEX onto water heaters?

[msteger]

Why does the title of this thread bug me? PEX onto water heaters?

Sorry..I just picked a quick title so I could start typing my question.

[KGarten]

KGarten:

Where does the draft hood opening come into play on a non- direct vent? Whether or not double walled connectors/ vents are used, there is that opening that will not insulate/ protect the pipe from the heat.

I would definitely count the draft hood as part of the vent in considering clearances. I went out and used an IR thermometer to shoot temps on my 50 gallon gas water heater while it was running. Water heater is in a closet in the garage. Temp at the fume hood edge where it flairs out closest to the water connections was 210 deg F. The temp for the 12" single wall vent above the draft hood was 100 deg F. The vent then has two 45 deg bends to offset the vent which had a temp of 145 deg F. It then transitions into type B double wall that had a temperature of 160 deg F. Temperature of the copper flex connectors closest to the 210 deg draft hood edge was 110 deg F.

It is my personal preference that the pex should stop in the wall and transition to copper stub outs with copper flex or solid connections to the water heater. If you have a leaking water heater that you are trying to shut off I would want my shut off valve in a solid material that I could easily get to instead of trying to shut off a valve installed on pex that is potentially flopping all over the place.

As an aside, a case could be made that a pex ball valve is not a full flow valve as required by code at the water heater. But that's a different story/argument...[]