Should I have a check valve on the cold water supply to prevent hot water from migrating out of the tank? How far will it go, with the tee from the supply being 8' above the cold water inlet? If so, what type should I look for? Also, does the DHW tank need its own expansion tank? I will have 80 gallons of water....neither our current home, nor our previous home had one. Our previous home also had an 80 gallon tank. If so, would I tee it off the pressure relief outlet?