As shown in the picture, I have green crust at the elbow of the copper exit pipe (I'm assuming its the exit pipe because its warm to the touch and encased in pipe insulation) coming out of the top of my water heater. It also drips a little. I know from reading other posts that I need to replace that elbow. I plan on replacing it with a Sharkbite corrugated stainless steel water heater connector.
My question is, do I need to drain the water heater before I cut the old copper pipe, or is it sufficient to just shut the water supply off to the water heater?
Also, is there any reason to shut off the gas supply to the water heater while I'm working on that pipe if I'm not sweating any joints?
There is no need to drain the tank. You will probably get some small amount of water on the floor but the tank will not run onto the floor. Make sure that the main water supply valve is shut off. The Shark Bite supply is a good idea. Get one with the valve build in. Just turn the control gas valve into the vacation mode while working on the water supply. Then back on again when done.