I am building a home and found out today that a standard flu from my mechanical room will not work to code. The plan was to place 2 50 gallon water heaters that are fed by a geothermal desuperheater. So my choices now are electric, powervent gas, tankless or some combination. I hate to use just tankless because I lose the free hot water the geothermal is creating in the summer. Any recommendations or insights would be much appreciated. TIA