bob_cntrctr

Gentlemen,

This will fit easily into the realm of over-kill, I know, I know....

Electric water heater has auxilliary H/C inlets on the side of the tank in addition to those on the top. The Hot out on the side is at the same level as the T&P fitting. Ever had nightmares about a T&P not working? So why not a second T&P in the Hot outlet on this tank for redundancy?

That is, can anyone think of a reason why installing a second T&P in the hot outlet of this tank would, other than being useless 99.9% of the time, be a bad idea?

Thanks.

thom

It's just one more thing to fail. I've never seen a T&P failure that resulted in an overpressure situation, I've seen many leaking T&P valves.

Plumber_Bill

Gentlemen You don't need double relief valves.

Just make sure that the one you have works!

Go to google type in Parrs Plumbing Allentown PA

My web site should come up there is a page called water heater explosions.

Take a look at the devestation no relief valve or a defective valve
can do. What is your water pressure 65 PSI The boiling point of water in your water heater is 312 degrees If you water PSI is 80 the B/point is 328 The valve is set at 150lbs the B/Point is 366 degrees.

Bill Parr LMP

protechplumbing

What the heck are you talking about. The T/p goes of if the temp goes above 215f so who cares about boiling point correction?

To the OP, a t/p CAN fail if installed incorrectly and fail in the closed position causing an explosion. A hole lot of things would have to be present at the same time but it COULD happen though you are more likely to be hit by lightening. There is no harm in installing a second valve with a second drain. If it's keeping you up at night, have a plumber put a second one in.........the right way.

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bob_cntrctr

OK, so, other than it's usually pointless and another part to fail, no real contra-indications.

Now, in this particular case it occurs to me that there already are two T&Ps - this place has two water heaters in-line with no back-flow check valve. So the pressure in one has to be the pressure in the other, so at least for pressure relief there's two.

Protech - I'll bite - other than screwing it into a tank tapping within 6" of the top of the tank and ensuring the temp sensor will be immersed (which is pretty much the only place you even can install it on most tanks), how would one install a T&P wrong?

Ron The Plumber

Easily done, there is two types of Residential T&P one can buy, seen by images below, using the wrong one on the wrong heater can mean disaster, one might try to use the short shank type on a thick liner wall tank, the type of tank that a T&P goes into the side of it, this can make one use a nipple and a coupling to make it work, doing so caused the probe not to be at the correct depth.

I have seen this and I have seen this on top of tanks before also.

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Plumber_Bill

PROTECHPLUMBING WROTE ...
What the heck are you talking about. The T/p goes of if the temp goes above 215f so who cares about boiling point correction?

Sir per your statement above ... I'm showing no correction just showing how much energy is used in raising the water to boiling when pressures are involved. And when all that energy is released all at once, like when a tank ruptures because of increased pressure. Usually the building goes along with the water heater.

You mention that the valve will go off over 215F. Think this one would have? Or even went off at 150 PSI the set point.

All I'm saying is that these valves should be checked. Pull the piping look in with a light -- corrosion -- what ever in the outlet or around the spring. Replace the valve!

Bill Parr LMP

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protechplumbing

There are numerous ways that one can be installed wrong and cause a dangerous situation. The fact that you don't know is exactly why you shouldn't be fooling around with water heaters because what you don't know CAN KILL YOU.

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protechplumbing

Yes, it probably would have gone off. The question is, would it have been able to relieve enough to to counter the amount of btus the heating device was putting in. Further, I don't see how that is relevant. You were talking about what the BP would be at 150psi as if the t/p would allow it to get that high. My point is that it wouldn't let it get that high because the thermal probe would expand at 215F and start relieving the heater.
What significance is the bp at 150psi?

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