Im sorry but you need recheck it. I dont know any thing in a house that would take 3 40amp c. Your furnace which is in a normal 2 story house is a 60 and 30. W/h Are mostly 30 amps. And tankless gas w/h are 120volts. So I think your lookin at it wrong. If you want and your not to far or you have a site I can go check it out.