Interesting that a whole house instant would
take that much amps.

thats because the water MUST be heated instantly, with electric its impossible, without at least a 200 amp service, and in a worse case, with low incoming water temp, in wither you could need 2 200 amp tankless in series.

that would be 400 amps to heat water plus 200 amps for you normal home.

wonder how much the power upgrade will cost?