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Water Heater T & P Valve Drain Line

north star

north star

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Joined
Oct 19, 2009
Messages
4,596
* * * *

I'm looking for discussion and input from you all......On the T & P valves,

what size and type of piping are you seeing installed?

From my observations, on most [ typical 40 gal. sized ] water heaters, the

T & P valve has a 7/8" sized opening......If the opening is 7/8", can you

[ by the letter of the code - referring to Section 704.2 and / or 504.6,

Item # 3, 2006 IPC ], install 3/4" sized cpvc or 3/4" pex and be

compliant?

My contention is that if the 3/4" cpvc is installed, that the inside

diameter has indeed been reduced in the direction of flow, and

reduced in size smaller than the opening of the T & P valve.

Thoughts...

FWIW, ...as some may remember, the missing "Uncle Bob" used to be

very adamant about this requirement........Even on the use of 3/4" pex.

Thanks for your input!



* * * *
 
The pressure relief valve exit is threaded and the 7/8 inner diameter is presumed that a threaded fitting will reduce the inner bore to 3/4". I think the concern about the pipe size reduction occurs with Pex pipe. The Pex has internal fittings that reduce the inner bore of the pipe from 3/4" to 9/16", A reduction of area by over 50%.
 
Agree with rshuey and jeffc in both cases.

Will not allow garden hose either!

pc1
 
PVC isn't listed for water supply (hot water)... CPVC is... water distribution piping is what is required. I don't know that you'd want to allow a reduction in the discharge diameter regardless of the material used.
 
* * * *

peach,

My thoughts exactly!......Plus, I want to know it if I am

incorrect [ according to the letter of the code ].

I actually measured the inside diameter of the 3/4 " cpvc

piping, ...it is 5/8" in diameter.

So, the question still is being posed......How many of you allow

this diameter reduction [ down to 5/8" i.d. ] in direct

disagreement with Section 504.6, Item #3, [ `06 IPC ]?

The reason that I am asking is that I have recently been

challenged on this requirement, in a Commercial application.

Your thoughts are encouraged and very much appreciated!

* * * *
 
The T&P valve manufacturer Watts require 3/4" ID from valve to the end of the discharge line.

3/4" CPVC and Pex do not meet this requirement.
 
If the ID is 7/8" how in the world would you get a 7/8" discharge to the termination point without a bushing that would create a sort of bottle neck if you will?
 
* * * *

David Henderson,

Good question!....I am not the manufacturer or associated with any

manufacturer, so what I am saying is only my opinion and experience.

IMO, the 7/8" opening at the T & P valve itself starts out with

the intention that any size of plumbing fitting [ an "increaser" or

a "reducer" ] will reduce the opening, at the T & P valve, down to

a designed 3/4" opening dimension......This "designed" 3/4" opening

is the dimension that is the dimension that is not to be reduced

over the length of the drainage piping.

Obviously, there will be some type of fitting attached to

the T & P valve to install the drainage piping to the point

of disposal......Sinced this specific installation point is not

addressed in the IPC or the IRC, and the fact that if the T & P

valves does open [ under pressure I am concluding ], I am erring

on the side of providing more piping diameter to accomodate

this pressure & hot water release rather than lesser piping

diameter......Also, I am taking in to consideration of Section

504.6, Item #6: Discharge in a manner that does not cause

personal injury or structural damage.

With a smaller diameter pipe, the probability of providing

a larger / greater sized bottleneck of pressure would be

created.....Again, IMO!......I would not want to utilize

the "god clause" provided in Chapter 1 - Section 102.9, `06

IPC, but I would want the system and its components to

operate in a safe manner.......I would encourage and review

any engineering reports or ICC ES Reports submitted in

rebuttal for using 3/4" cpvc or pex, ...or even 1/2" cpvc

or pex, ...or even 1/4" cpvc or pex [ "tongue in cheek" ].

Since we are discussing the "letter of the code" [ which is

what I asked for ], let us take into consideration all aspects

of the "letter"......If someone wants to install something smaller

than the 3/4" inside diameter, then please submit the appropriate

reports that will allow it.........Some on here might say that by

using this clause, I am abusing my position......I would

respectfully counter with "It is my intention to provide the

safest operation of the components installed.......If your

submitted data will support a smaller sized pipe, then I will

go by what the elected officials and AHJ leaders direct me to

do.".....Until directed otherwise, I will require a larger sized

inside diameter of the drainage piping and not worry about

the contractor or homeowner who is attempting to save money

on a smaller sized pipe.......No disrespect to you or others!

Also, if there is another means to attach approved sized

materials for this pressure relief valve, ...please list it on

here so I can learn about approving another type of

installation, ...as approved by the manufacturer of the

T & P valves.

Thanks!



* * * *
 
* * * *

Thanks " mtlogcabin " for the article......It's a good read! 8-)

Also, "Much Thanks" to Uncle bob for his passion on

plumbing and other codes as well. [ Hoping that you will

reconsider and rejoin this code forum Uncle Bob ! ].

* * * *
 
IMO I don't believe PEX plumbing meets any required working tempatures for a T&P and the inside dia. of 3/4" PEX is 0.677 and that's before the insert fitting is added that reduces flow even further like an hour glass or like your postrate.

The closest Working temp. of PEX, 100PSI at 180degrees F does not meet the T&P pressure valve requirements.

pc1
 
* * * *

Pcinspector1 ( and others ),

Can you please provide documentation / a link regarding the

PEX non-compliance!......I will need it to defend my position

of "not" installing it on T & P valves......The plumbers around

here will just love it when they cannot use it on T & P valves

any longer.

& & & &
 
north star,

Try the ICC-ES/ESR-1929 report.

3.1 Tubing pressure-rated for 100PSI @ 180 degrees and the insert fitting reducing the flow dia.

also see 4.2 about PEX should not be uses within 18" above the water heater on the supply side.

Our water heater at work has a WATTS 3/4" 100XL, 150PSI- 210F max. T&P which is pretty common I think? Would'nt the pipe melt or get soft if the T&P was to discharge?

pc1
 
The securing of PEX could also be a problem when using it on T&P valves.

Also doesn't most T&P valves require rigid pipe???? PEX is not a rigid material! Just thinking.....
 
* * * *

Pcinspector1 ( and others ),

The Zurn [ brand ] PEX tubing can be installed on T & P

valves according to their manufacturers installation

literature.....See Page 23 in this link.

http://www.zurn.com/images/pdf/zpm07199.pdf

" Water Heater Temperature and Pressure Relief Valves


Zurn PEX tubing may be used on the discharge side of a

typical water heater temperature-pressure relief valve."



​
I'm thinking that there are different types of

manufactured PEX tubing, ...with different design

characteristics.

So, should we be allowing the pex on T & P valves or

not, ...whether Commercial or Residential?



* * * *
 
north star,

Just goes to show you what I know. I'll start looking for the external PEX connection fittings that will no doubt be designed next to prevent the flow from being reduced from 3/4"

pc1
 
& & & &



Pcinspector1,

That's o.k.!......At least you are trying to help in my search for information

and application of the published codes.

Thank you ( and the others ) who are assisting! :agree

FWIW, the Zurn web site also has some opportunities for FREE online

CEU seminars - http://www.zurn.com/pages/education-main.asp

% % % %
 
2009 IPC 504.6 Requirements for discharge piping. The discharge

piping serving a pressure relief valve, temperature relief valve

or combination thereof shall:

13. Be constructed of those materials listed in Section

605.4 or materials tested, rated and approved for such

use in accordance with ASME A112.4.1.

TABLE 605.4

WATER DISTRIBUTION PIPE

Cross-linked polyethylene (PEX) plastic tubing ASTM F 876; ASTM F 877; CSA B137.5

Cross-linked polyethylene/aluminum/cross-linked polyethylene (PEX-AL-PEX) pipe ASTM F 1281; ASTM F 2262; CAN/CSA B137.10M

Cross-linked polyethylene/aluminum/high-density polyethylene (PEX-AL-HDPE) ASTM F 1986

Code allows PEX however it must be secured according to specifications. What is that????? Every 32"............. Wonder if it 90's straight down...do you want to screw a fastener into the water heater? Does it require rigid pipe???
 
& & & &



Section 504.6 [ from the `06 IPC ] does not provide Table 605.4

for application of fastening / support of the pex type tubing.

I could not "require" the 32 inch fastening dimension!



Beginning in the `09 IPC, ...it does require the 32 inch fastening

dimension......I wonder how the plumbers will be anchoring the

pex tubing with this "new" requirement...



$ $ $ $
 
Last edited by a moderator:
504.6 # 13 specifies that the discharge pipe of the T&P be constructed of materials specified in Table 605.4. Table 605.4 lists PEX as one of the materials allowed for T&P discharge pipes.

I would think it was sanitary also however the code refers you to water distribution......

I think the rigid pipe come from the manufacturers recommendations....... I think.... I'll do a little more research! But I may also be having flashbacks from the 70's! :)
 
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