Hello, Jill and Ken.
I’d like to use the Eemax unit (pictured below) as my tankless hot water heater. When you click on the link of the Installation Guide, you’ll see what’s required for this model—i.e., 3 dual pole 40 Amp breakers. I have 3 Siemens Q240 40 Amp Dual Pole Circuit Breakers. Additionally, I purchased an Aqua-Pure Scale Inhibition System to be routed to the input of the Eemax unit. The open breakers are highlighted in green:
Eemax Installation Guide