water heater over temp (T & P ) valve piping question

Discussion in 'Water Heater Forum, Tanks' started by npreiser, Jun 25, 2014.

  1. npreiser

    npreiser New Member

    Messages:
    1
    Location:
    Oregon
    During home inspection, I found that the hot water heater T&P valve piping used cpvc(not copper) , which
    is supposedly OK. The piping from the T&P value turns in the upward direction, for over 4+ feet, going 2+ feet above the top of the hot water heater,
    then goes horizontal...and then down, to a drain, with a total run well over 25ft

    Reading online and the manual for the heater says that the piping should allow gravity feed, which
    implies it should never go upward.

    Any suggestions/opinions would be greatly appreciated..
    Is this acceptable?

    This is a replacement heater in a 1950s home ,in a location that did not include a drain(hence the nonstandard install).



    Nick .
  2. dj2

    dj2 Member

    Messages:
    418
    Location:
    California
    "Is this acceptable? "

    Not in my city. It should be all 3/4" copper, drain to the outside, no more than 6" above grade.
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,052
    Location:
    Bothell, Washington
    I see plenty of CPVC relief lines run in Seattle and approved by the inspectors.
    However, they all run downhill.

    If we have a situation where we can't drain them downhill, we still run the relief down from the water heater.
    As high as we need to be, we place a 125 PSI relief in a location where we can drain it.
    This may be on the cold line. The idea being that this opens before the T&P on the water heater. The water heater T&P may never, ever need to open up if you have a 125 PSI relief on the incoming cold.
    Last edited: Jul 6, 2014
  4. Reach4

    Reach4 Active Member

    Messages:
    2,303
    Location:
    IL
    I have a hard time seeing how going a few feet uphill rather than relying on gravity is going to conceivably cause a problem. I guess it would be some condition where you had over-temp but not pressurized?

    On a different note npreiser, what software is it that changes "valve" into "value"? I have seen that substitution made several times before.

    dj2, maybe this would be a good application for galvanized in your city, but you probably don't carry that. :)
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,052
    Location:
    Bothell, Washington
    If you have leakage from the T&P and it can't drain out, it can become blocked over time and useless.
    First rule of plumbing, it all has to go downhill.

    A water heater with a blocked or plugged T&P has been known to explode through the roof and land blocks away. It's rather serious.

  6. On another site I am catching all sorts of hell for useing cpvc
    on my t+p drain line... even though it is ok in Seattle and most parts of the country everyone over there thinks their code is the best......

    [​IMG]

    The real problem with running the t+p uphill from the heater is over time the line could fill up with water.... once it begins to fill up with water , the water becomes soiled with bacteria and other nasties.... stagnant water....

    If the t+p is leaking and the water is ever turned off in the system
    there can be a back pressure or siphonage through that t+p and all the nasty water that has been laying in that line will suck back into the water heater.........

    Correct me if I am wrong but I think that is called a potential
    cross connection ....and if it makes anyone sick or not depends on the situation... I dont know how much botulism or bacteria it would take to make someone sick if they were to brush their teeth with hot water or whatever....
    Last edited by a moderator: Jul 8, 2014
    Terry likes this.
  7. Reach4

    Reach4 Active Member

    Messages:
    2,303
    Location:
    IL
    You and Terry have stated good and logical reasons. My thought that there was going to be plenty of pressure to drive the water uphill had flaws.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    quote; I have a hard time seeing how going a few feet uphill rather than relying on gravity is going to conceivably cause a problem. I guess it would be some condition where you had over-temp but not pressurized?

    The real problem is that the T&P valve has a metal spring. If the discharge goes "uphill" the spring is ALWAYS in the water and WILL corrode to the point where it either cannot open or cannot withstand the system's pressure. A secondary consideration is that in certain conditions the trapped water could freeze making the valve inoperative.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    As far as the CPVC goes, here, they take the requirement that the discharge be "full size" literally which means that 3/4" CPVC is NOT 'full size'. We cannot even use a water heater flex line because the corrugations reduce it to less than "full size".




  10. that is a bummer..... We use the cpvc all the time and it appears to
    be full size to me,, unless they are quibbling over 2/62nd of an inch
    I always heard they did not care for cpvc because of the scalding water issues through the t+p valve.......

    I use the flex lines all the time on the heaters in our town with no issues
    what so ever.... I dont understand what the difference is considering
    if it goes through a water softener it usually gets reduced down under a
    half an inch ... And of course it gets reduced down to 3/8 at most faucets..

  11. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    Some places want the T&P to go outside. Places that require this may have provisions for when this isn't practical. I've seen documentation for cities in Calif. to run the T&P uphill, for instance. Here is an example:

    http://www.cityofpaloalto.org/civicax/filebank/documents/17800

    In this case, they use a small drip line off of the T&P discharge to detect small leaks.

    In terms of CPVC, the OD is the same as copper, but the ID is smaller. So, if the WH is fed with 3/4" copper, then an inspector may say the CPVC on the T&P is not "full size". If the whole house is CPVC, I don't see how they could make the same argument..but they may try anyway. :)
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