When does a water heater not require a T&P valve

lazypupJanuary 27, 2012

Here is a simple question that any first year apprentice can answer.

Under what circumstance do you not install a Temperature & Pressure relief valve on a water heater??

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dadoes

I'm not even a 1st-week plumbing apprentice, but AFAIK only if it's a tankless unit, as per if allowed by local codes.

    Bookmark   January 27, 2012 at 9:44AM
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lazypup

There is one instance when a tank type unit IS NOT fitted with a T&P valve

    Bookmark   January 27, 2012 at 10:12AM
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lazypup

I'll give you a hint, this situation commonly found in residential applications and sadly nearly every one is installed incorrectly even thought the solution is common to all plumbing codes.

And sadly, even many plumbers do it wrong

    Bookmark   January 27, 2012 at 2:02PM
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davidro1

if it is the first of two in series, it requires other things than a T&P valve. The last in the series gets the T&P valve.

    Bookmark   January 28, 2012 at 3:41PM
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lazypup

Wrong,,,,the T&P valves are sized to the burners and even when two or more are in series or tandem, each must have its own T&P except for one circumstance.

    Bookmark   January 28, 2012 at 4:56PM
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bus_driver

The only exception in the NC Plumbing code (they have their own version of the IPC) for automatic water heaters that operate above atmospheric pressure is for heaters larger than 120 gallons. The T&P valve must be approved by both ASME and NBBPVI. Perhaps you are referring to heaters that are at atmospheric pressure- like those on the end of the wood cook stove from my childhood.

    Bookmark   January 28, 2012 at 5:27PM
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lazypup

I am referring to standard water heaters that operate at the standard line pressure for potable water..and I can assure you, it is in the NC code

    Bookmark   January 28, 2012 at 5:47PM
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zl700

a. Pressure vessels used for heating water or storing water at pressures above atmospheric shall be protected by approved safety devices in accordance with one of the following methods:
1. A separate pressure relief valve and a separate temperature relief valve; or
2. A combination pressure and temperature relief valve; or
3. Either "a" or "b" above and an energy cut-off device.
4. Tank construction conforming to a standard that does not require a temperature or pressure safety or relief valve.

    Bookmark   January 28, 2012 at 10:43PM
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lazypup

zl700 has the answer, but now let me explain a bit futher.

Code mandates that when a T&P valve is installed we must attach a FULL BORE gravity flow drain line to the output of the T&P valve. All horizontal portions of that drain line must be pitched at a minimum of 1/4" per foot downward towards the discharge end of the pipe and the pipe MUST BE terminated outside the structure or into an approved indirect waste receptor.

At a minimum, if the water heater is installed in an unfinished basment or utility vault that has a floor drain, the line from the T&P may go straight down and discharge at a point not more than 18" above the floor. The water may then run across the floor to a floor drain or sump pit.

It may also be run to a utility sink, floor drain or sump pit providing the discharge end of the line remains a minimum of 2" above the flood level rim of the receptor.

HOWEVER: in some instances such as in homes served by a septic tank or where the municipal sewer lines are shallow the house main drain enters the structure at an elevation which is too high to achieve a gravity floor floor drain or even a utility sink and some of those structures do not have a sump pit.

In a situation where you cannot achieve a gravity flow to an approved waste receptor such as described above, the T&P valve is removed and replaced with a WATTS 210 gas valve. The gas supply line for the water heater is then connected to the input side of the Watts 210 gas valve and a line is connected from the output side of the gas valve to the water heater burner contol. If the temp or pressure in the water heater were to then exceed the mandated limits the Watts 210 valve will shut off the gas supply to the burner.

When the Watts 210 valve is installed on the water heater you must then go to a convenient point above grade and install a "pressure relief valve" and terminate that through the wall to the exterior or into an approved waste receptor.

    Bookmark   January 28, 2012 at 11:14PM
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davidro1

1./ if gas water heater
1./.a./ if drain out of house is higher than basement floor
1./.a./ A./ if there is NO sump pump
Then use a gas shutoff.
ANd also, do not intall a T&P

(?)

is this it?
is this clear?
is this common?
is this really the way it is? Not to install a T&P?

?

    Bookmark   January 30, 2012 at 8:45AM
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