This is Turtle.
Davey , Putting a cellinoid valve with compression fitting on the gas feed line up in a burn area is not really a good ideal. When the compression fitting are heated up then cooled off over a few years they could loosen up and let the cellinoid valve just fall off and when the gas valve open for to heat the water. It would fire up about 1/2 the room with burning gas shot from out from under the water heater by a open pipe. Also how long do you think the plastic cellinoid valve coil is going to last being heated up all the time at burner flame temperatures.
I can't remember for sure but didn't we have a conversation about you using 3" PVC pipe for to vent a gas water heater with and you said it worked fine for you. Correct me here Dave about this !