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Thread: T&P valve drain plumbed up!

  1. #1

    Default T&P valve drain plumbed up!

    That last hot water tank thread reminded me of a question:

    In my new apartment, my gas HW tank has it's T&P valve drain plumbed straight up to the roof, instead of down to a floor drain. I'm sure this must not be to code, but is it at all dangerous? Notice the nice looking hole in the ceiling where my HW tank vent is.

    Also, I thought I'd show you all my vintage 1970 style mustard color appliances. The frig is especially functional, with its tiny freezer compartment that requires manual defrosting every 3 weeks. Who says G.E. doesn't make products that stand the test of time!
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    Last edited by Verdeboy; 11-16-2006 at 11:17 PM.

  2. #2
    In the Trades Gary Swart's Avatar
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    There was a thread dealing with this just yesterday. You should go down and read what was said, but in brief, the TP always is supposed to go down. I supposed the way yours is plumbed is better than putting a solid plug in the tank, but is sure isn't by any code I can imagine.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default T&p

    It is illegal for the discharge to go in any direction other than continuously downhill to the discharge point. This is for at least two reasons.
    1. The first time it discharges the pipe will fill with water. The exposed spring in the valve is steel and since the water will stay in the pipe the spring will rust and will eventually seal the valve closed so it cannot open and discharge if needed. At that point your water heater becomes three sticks of dynamite waiting for someone to light the fuse.
    2. If you are in a cold climate, the water in the pipe could freeze causing the same situation as if the spring was completely rusted, with the same results.

    You might be better doing what one "creative" customer did. He piped the relief pipe into the chimney, figuring that if it discharged the water would put out the burner and pilot and then the safety unit would kick in and turn off the gas. This is more in jest than a real suggestion, in case you think he had a good idea.

  4. #4

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    I don't think we have the same laws and codes here in SW New Mexico as everyone else has. It's still a part of the old wild west.

    If there's no check valves or PRV's, then wouldn't any excess pressure just backflow to the street main?

    The managers here are reluctant to fix even the tiniest thing, and they frown on me doing any work. Makes them look bad.

  5. #5
    Renovator Gencon's Avatar
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    Only if the main valve is open.

    This is a pressure and temperature relief valve we are talking about here so if the water heater gets too hot, it will discharge. When the relief valve discharges hot water, cool water is admitted back into the tank, thus cooling things down. If this didn't happen you could possibly boil the water in there and create steam, and then it will pressurize the tank and as the pressure increases, so does the boiling temperature of the water.As this all builds up, there is the possibility of the whole thing literally exploding with superheated water and steam.

    It would be criminally neglectful for local authorities not to have this as part of the code.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default T&p

    Ideally, yes it would, except if you happened to have shut off the main water valve. OR if the heater is overheating which has nothing to do with the pressure, until it reaches the boiling point, and then the amount of damage it will do to your house will be directly proportional to the city's pressure. Although you may not be around to read about it in the newspapers or see it on the 6 o'clock news, with pictures.

  7. #7
    Plumber solsacre's Avatar
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    Up is sometimes better than no drain....

    I don't buy that but some codes have in the past...

    I don't remember well but I think that some codes (Oregon) allowed you to run a T&P up if and only if you drilled a 3/32 hole in it's lowest point so that It could drain any minor leaks and not rust the t&P. It has also been suggested to me that the hot water and cold water in the t&P hitting can cause an explosive combonation (Can't make me a beliver to that). You may want to look at the under side of them two 90's and see if it has a small hole in them... If not at least put one in.

    Dances-with-pumps

  8. #8

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    Good idea. They won't even notice I drilled that little hole.

    I could turn them in for all sorts of violations: safety, fair housing, smoky rental office, but it's the only place around that doesn't allow dogs. There's more dogs per capita here than anywhere I've ever been, and they bark all day and night.

    My ears used to hurt from the earplugs I needed to wear all the time.

  9. #9
    Plumber jimbo's Avatar
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    The pipe on the left looks like B-vent, so it need a 1" clearance where it goes thru the ceiling. Looks like a violation. What is the lager pipe on the right?

    Things like this may be the reason for the short life expectancy of the population of the "wild west" !

  10. #10

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    Quote Originally Posted by jimbo
    The pipe on the left looks like B-vent, so it need a 1" clearance where it goes thru the ceiling. Looks like a violation. What is the lager pipe on the right?

    Things like this may be the reason for the short life expectancy of the population of the "wild west" !

    The large pipe next to the hw tank vent is just hanging out of the ceiling. It's an open vent attached to nothing. I'm sure it's probably allowing undesirable exhaust to suck back in the apartment. I've got a CO detector, and so far it hasn't gone off.

    Just as an aside, almost half of my customers are tethered to oxygen tanks for one reason or another. There's was, and still is, an awful lot of mining going on here.
    Last edited by Verdeboy; 11-18-2006 at 01:05 PM.

  11. #11
    Plumber/Gasfitter dubldare's Avatar
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    I can't believe that anyone who has responded to this thread hasn't noted that the discharge line is reduced to 1/2".

    T&P valves are rated for specific BTU ratings. A standard, residential water heater usually is equipped with a 100K/btu relief. A standard, residential gas water heater is generally 40k/btu.

    In all cases, the rating of the T&P valve must exceed (generally by a very large margin) the burner capacity of the equipment it is connected to.

    To restrict the outlet of the T&P valve serves to de-rate the relief capacity of the valve. It should also be self-evident that excessive offsets and length of the discharge line would also cause de-rating of the valve. Likewise, scale and mineral deposits that form around the valve over time serve the same. That is one reason why they are oversized from a capacity standpoint.

    To me, piping a relief valve upward is completely assinine. Irregardless of pipe size, there is a potential for having to overcome head pressure of water which may trapped in such a line- .434 psi/ft.

    Sure, the 3/32" hole might keep that head from happening, but I feel this entire premise is disturbing.

    The relief valve is there solely to keep the WH from blowing up through the roof. It will ONLY discharge if there is a malfunction.

    Where I'm from: relief discharge lines shall be piped fullsized toward an area of safe disposal, such piping shall be downward with minimal horizontal offsets, if more than 4 offsets are used, pipe size shall be increased; at no point shall the discharge pipe trap water.

    These dunderhead inspectors and AHJ's should really start getting back to basics. Instead of worrying about a little bit of water on the floor, maybe they should worry about what could happen. For pete's sake, the heater will most likely leak before the relief has a reason to go off!
    --Customers of plumbers: Never be afraid to ask for proof of licensure of the plumber servicing your equipment. A licensed plumber will be proud to show you his personal license.--

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