So I have this idea about how to use the heat that my gas water heater is shooting out the exhaust to preheat water going into the water heater, thereby using less energy. I noticed that the exhaust pipe gets pretty hot, so I was thinking about wrapping a soft copper pipe around it and running the inlet water through the copper pipe with the outlet of the copper pipe going into the cold inlet of the water heater. I figured I could get around 50 feet of pipe around the exhaust pipe, which I figure would raise the inlet temp of the water to the heater significantly. My question is if I should be concerned about adding a T&P valve somewhere, in case the water in the pipe would get too hot from sitting next to the exhaust when the heater was heating and no one was using the water. Does someone who knows plumbing know if this could work and how I would make it safe? Thanks.