504.6 Requirements for discharge piping-
The discharge piping serving a pressure relief valve or combination thereof shall:
1- Not be directly connected to the drainage system. Could create a cross-connection with the potable water and drain system. Under certain conditions, drain water could be pulled into the water heater. Also it makes it difficult to determine if the valve is leaking and in need of replacement or repair
2- Discharge through an air gap located in the same room as the water heater.
3- Not be smaller than the diameter of the outlet of the valve served and shall discharge full size to the air gap.
4- Serve a single relief device and shall not connect to piping serving any other relief device or equipment.
5- Discharge to the floor, to the pan serving the water heater or storage tank, to a waste receptor, or to the outdoors.
6- Discharge in a manner that does not cause personal injury or structural damage.
7- Discharge to a termination point that is readily observable by the building occupants.
8- Not to be trapped.
9- Be installed so as to flow by gravity.
10- Terminate not more than 6 inches above and not less than two times the discharge pipe.
11- Not have a threaded connection at the end of such piping.
12- Not have valves or tee fittings.
13- Be constructed of those materials listed in section 605.4 or materials tested, rated and approved for such use in accordance with ASME A112.4.1.
14- Be one nominal size larger than the size of the relief valve outlet, where the relief valve discharge piping is installed with insert fittings. The outlet end of such tubing shall be fastened in place.
-2018 Int. Plumbing Code