I think this is ill advised if not totally wrong. New house up for 1 year warranty, passed city inspection.
I plan to recommend a second water heater, unless a plumber out there disagrees with me.
Just to be clear, my problem is with recirculating the water that passed through the underslab lines back into the cold side of the wh along with the water main water, not the use of a domestic water heater. The underslab lines are for the basement slab, maybe close to 1000 sq feet, hundreds? of feet of PEX lines.