Kbeck can install commercial water heaters of all sizes. This installation is a light commercial tank, 100 gallons and 80,000 Btu. It serves four units.
It is an A.O. Smith model with a recirculation system. Note that the tank is properly valved for flushing air from the piping. This is important because if it's not done, trapped air can run down the recirc line and burn out the pump. What is proper? There has to be a way to close off flow from the tank, or in some cases, the incoming cold line, depending on where the recirc line returns to, and force flow through past the pump and out.
We have talked up expansion tanks in other sections. There is none here because the owner declined to pay the extra cost. That is a client option, but we won't budge on code issues like earthquake straps. We've encountered installations where the plumber DID budge on that. It's both unwise and illegal.
We've also talked down gate valves. There is a big difference between cheap gate valves, often found on residential water heaters and high-quality ones, which can be as good as ball valves.