Hot water tank pressure relief

I was staring at this valve the other day - yea, I have no life to speak of - and saw how the end was not vented into anything. There aren't any drains nearby but I was thinking that a PVC standpipe with a hose coupling at the bottom would handle the catch and the draining. THe question is, how much water is vented when a valve opens? That would determine the diameter of the standpipe. TIA, C
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how
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Some areas of the US will not allow the temp/pressure valve to be vented inside. at least not any more. When one goes on temperature it can be really dramatic. It will vent until the temperature/pressure is low enough for the valve to reset. Diameter of the vent depends on the length of the pipe and number of elbows. PVC is a really bad idea. If the relieve valve goes cause of temperature then the PVC is going to melt. All of the drains I have seen are usually in copper pipe. I remember seeing a really old installation done in galvanized pipe.
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C & M wrote:

The most common amount is just a few ounces or less. If the valve fails, it could be thousands of gallons, but this kind of failure would be very rare. I think the most usually would be only a gallon or two.
--
Joseph Meehan

Dia duit
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From a few ounces to a few hundred gallons. Sometimes these valves open and do not reseat properly and the water will continue to run until you shut the inlet valve.
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Since there isn't a drain anywhere near I'm wondering if I could rout this upward and out the sill ot the outside. But then I'd have a critter or insect issue. Guess I'd better call a plumber.

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C
IIRC, The relief valve discharge pipe should be 15 feet or less with a maximum of 4 elbows. That would be 3/4" pipe or tubing. More elbows or more pipe would require larger pipe, like 1". Under NO circumstances should the pipe run uphill for even a short distance. It should terminate outside between 6" and 18" above finish grade.
Stretch
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