I want to buy a tankless water heater to replace my old tank style. Our water is so hard that sludge builds up in the tank. I checked my box and the main breaker says "200" on it, so I'm assuming I have a 200 Amp breaker panel. There are 40 numbered "slots" on the panel, but several of them aren't open (i.e. have metal from the panel box covering them). I do have three slots with knockouts in them, but it looks like most of the installed breakers say 10ka. How do I know if I have enough room? Here are the specs for the water heater: Requires 240V Hard Wiring and 120 Amps. This Model Requires 3 Separate 40 Amp 2-Pole Circuit Breakers and Six #8 Awg Wires + Ground (Min. 200 Amp Breaker Panel) Of course I will have this professionally installed, but I don't want to order the thing only to find out my panel can't support it.