we have been there already, as Beers' reply hints. if you have 4 magnetrons, and only 2 are ever firing at the same time, then the max heat you can put into the water is the sum of the ratings of 2 of the magnetrons. with 4 rated at 1500 watts each the total heating ability, 6000 watts, is way below other electric tankless units that claim to supply a (one) small bathroom usefully