you can do zoning with a geo unit, but they are right you loose efficency, zoning is more for comfort. not all geos do the hot water for the house, they can but doing a on demand hot water heater is normally better in the long run. Geos are the way to go you can also do thing like a duel fuel system if geos are out of your price range then doing a heat pump with gas back up is another option prolly second best to a geo