My home has two 40 gallon gas-heated water heaters and since we figured we need just one for our needs, I shut-off gas supply to one of the heaters (should save on gas bills). Since the 2 heaters are in "tandem", they have a copper pipe for transferring water from one tank to the other. I checked the plumbing around both tanks and it impossible for me to figure out which tank supplies hot water first before it 'reaches in' to the other tank.
So now, I am at a loss to figure out if I had turned off the right tank. What if I turned off the "primary" tank, in which case, I would end up getting water from the secondary tank that is mixed in with cold water from the "primary tank". This would really make it worse since the water I would get out of the faucets would always be 'tempered' with cold water from the tank that I shut-off.
I thought about this for a while and figured that if I shut-off water supply to (cold, pre-heated water) the tank that I cut the gas supply to, then I would not have the aforementioned issue. I looked for a water shut-off valve, but all I could find was a small, green-colored valve that turns only 90 degrees - open or close, on a pipe that goes into the tank. This pipe is going in to the tank just above where the pilot knob is (the water heater is made by Reliance).
So, my question is: is the small, green-colored valve the right water shut-off valve to cut-off water to the tank? This valve is not something you can rotate - it is a simple, open/close type that only turns 90 degrees.