Can 3/4 Pex be used on the t-p valve drain line? Any problems with it being able to handle the discharge temperature and pressure? Is 3/4 Pex id too small? If it is too small can 1 inch Pex be used?

Code requires no reduction in pipe size. I believe that you'll find the I.D. of 3/4" pex is less than the T&P vlalve. Also, code requires that the piping used to discharge T&P relief blowoff be rated to receive said temperatures and pressures...

Jason

I believe that our code here, (NYS/IPC) requires that the WH T&P to be hard-piped, I think
coiled PEX may have the tendency, and possibility to hold water if not installed correctly.

Many WH's around here discharge straight down, to within 6" of the floor, (where a blow-off
would not cause property damage), otherwise it goes to a proper receptacle or outside.

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"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.

While we're talking T&P piping.... When I converted to gas WH I installed it in a shed built off the back of my house on concrete patio. Piped the T&P around the tank and out a hole in the wall of the shed, then down to the patio concrete where it dumps. Used 1/2" CPVC. Inspector never found a problem with it...!

Recently, I find two potential violations:

1) Reduction in pipe size. Seems I should use 3/4" all the way.

2) I have read (I think in WH install instructions -- not sure) that the pipe connected to the valve should flow downward, not horizotal like mine does. This I do not understand, because some tanks install it in the top, and in that case they must flow horizontal at least for a foot or so...

I guess I could simply pipe it directly down to 6" off the floor and let it splash all over the shed if it blows. Might actually splash out the pilot and shut itself down...

Would that be a good thing.....?

I hope you fixed it because what you have there is a potential bomb.

Pex piping off of a t&p valve is not a good idea and in most places not code. Use a piece of copper. As far as it turning the water heater into a bomb, funny! Your water heater would NOT be turned into a bomb unless the actual t&p valve was stuck shut.



Edited 1 times.

if the inspector allowed cpvc to be used im sure he will allow strait pex or a cheap way for rigid pipe is the depot they can cut and thread a piece of black gas pipe for you, 6" above the floor if piped into a drain you will not see the leak and not know you have a bad t&p valve.

Ive seen a T&P valve out the of a WH with a 45 off the nipple and a 1' piece of black pipe pointed straight at your face, very scary.



Edited 1 times.

3/4 cpvc is very common for the T&P in my area...its rare to see copper used on a new install.

i would think straight pex would work.

Quote: 6" above the floor if piped into a drain you will not see the leak and not know you have a bad t&p valve.

Why not? If it's 6" above the floor, a leak from the T&P would be obvious, if properly piped to a floor drain the T&P discharge would clearly be noticeable - better than being piped to an area in the rear or the side of someones house where they might not ever go near.

e-plumber
-----------------------------------------------------------------------------------------------------------------------------------

"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.

OK so we don't reduce the T&P outlet why?

If the water heater can not relieve pressure at a rate faster than expansion than where do you suppose all that pressure is going?

Chance of it happening? probably one in a few million, but then someone always wins the lotto don't they?

IPC 504.6.2 Relief valve materials shall be of those listed in table 605.5 or shall be tested, rated or approved for such use in accordance with ASME A114.2.1.

Table 605.5 includes Pex, PolyButelyne, CPVC, copper, galvanized steel.

IT depends on how your building department interprets the requirement that it be "full sized from the relief valve to its termination". A strict interpretation, used in this area, requires that it have a 3/4" i.d. for its entire length, which precludes 3/4" plastic of any kind, and even corrugated copper connectors for the initial connection.

Used 1/2" CPVC. Inspector never found a problem with it...!

2) I have read (I think in WH install instructions -- not sure) that the pipe connected to the valve should flow downward,

In the "old days" in this area the relief valve discharge was 3/8" o.d. copper tubing run up to the roof. Horizontal is not the problem. Going horizontal AND uphill is a problem.


I guess I could simply pipe it directly down to 6" off the floor and let it splash all over the shed if it blows. Might actually splash out the pilot and shut itself down...

Would that be a good thing.....?

I had one customer who ran the above mentioned 3/8" copper into the heater's flue. His theory was that if it discharged the water WOULD extinguish the pilot and burner flame.

Some people just love to use hyperbole to get their point across. Scam plumbers do it all the time to scare customers into unnecessary repairs.

The discharge pipe is supposed to be of a material approved for water piping. Black pipe IS NOT approved for use as water piping, and COULD corrode shut, or restricted, due to moisture.

quote; if piped into a drain you will not see the leak and not know you have a bad t&p valve.

You do not "pipe it INTO a drain". The code requirement is that it terminate ABOVE the drain, for several reasons, one of them being that you WOULD see any discharge if you were observant.

quote; If the water heater can not relieve pressure at a rate faster than expansion than where do you suppose all that pressure is going?


Time to go back to water heater safety school. The T&P valve is not relieving EXPANSION, it is relieving ENERGY being created by the burners or elements. It does that by introducing cold water in an attempt to cool down the temperature in the tank. IF that does not happen faster than the burner is adding energy, the tank will eventually explode when it reaches a critical situation. The smaller discharge line WILL reduce the rate of energy release.

That governs the material. ANOTHER section governs the size requirement.

That is another restriction here that I did not mention in the previous posting. Soft copper is also not permitted because it could be deformed by bending and thus is also prohibited.

What YOU think is immaterial. IT is what the INSPECTOR thinks that governs the installation. Here, you could think all you want, but the inspector would still reject it.

Author: nhmaster3015 (NH)
OK so we don't reduce the T&P outlet why?

If the water heater can not relieve pressure at a rate faster than expansion than where do you suppose all that pressure is going?

Chance of it happening? probably one in a few million, but then someone always wins the lotto don't they?



hj has the right answer on this one. If you just pumped up the pressure in a water heater to, say 160 PSI ( no TP ) the releasing a very small amount of water, perhaps a teaspoon or cupful, would lower the pressure to near zero, as water is only very slightly compressible, and very little stored energy exists from that aspect/

BUT, you have a heating element adding energy to that equation, and you get into the whole sensible heat/laten heat business, and bottom line you do have a bomb! That is why TP valves are rated by BTU. That is the amount of energy they are capable of relieving. Their BRu spec must equal or exceed the BTU input to the WH/

QUOTE: Pex piping off of a t&p valve is not a good idea and in most places not code. Use a piece of copper. As far as it turning the water heater into a bomb, funny! Your water heater would NOT be turned into a bomb unless the actual t&p valve was stuck shut.



Ya but I wanted someone else to splain it. Thanks HJ, I should have differentiated expansion from the release fo energy but either way the effect is the same.



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but either way the effect is the same.

I am not sure what you mean by effect, but the RESULTS would be vastly different. The difference being whether you had a wet floor in the house. Or a dry floor and NO house.

I was going for the no house result. If the pressure in the tank builds at a faster rate than the relief valve can relieve it..

And as many people have found out the ultimate way to slow down the release is a plug in the T&P valve, and it gets the fastest results.



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www.watts.com has a video of water heater tank explosions that they produced back in the 50's. Some great footage there. I believe it's a free download though you can get that one and one on scalding and another on backflow all on dvd for free also. Really eye opening stuff. Particulary the scalding vid.

and nhmaster what you failed to read or at least mention is the section about relief valves says the pipe must not be smaller than the diameter of the outlet of the valve served and that pipe must be full size all the way and must not have threads at the end of the pipeso that leaves out screw pipe and plastic pipe especially pex

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Here, all you had to do was look in the newspaper a couple of months ago to see the remains of the house and the water heater several hundred yards away. And if you were the homeowner, all you could do was have the house bulldozed level, and then finish paying on the mortgage because the insurance company refused the claim because of "tampering" by putting a plug in the T&P valve.

I only posted the code requiring acceptable pipe, not the supporting text, you are correct. You can not use pex because of the (god I almost hate to say this again) restriction.

Is the actual t-p valve seat diameter 3/4 inch?