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

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.

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.

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.

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