I guess I will start at the begining. I build my home just over 4 years ago. At that time I installed in floor radiant heat throught the home. I installed a 185,000 BTU tankless water heater for both DHW and the radiant. Two years ago, I got tired of filling my 500 gal propane tank on a monthly basis in the winter. Or rather paying for it, so I installled an OWB. This is working out just fine. I have the two systems running together. When the temp falls ( ie. my wife doesn't feed it while i'm gone) in the OWB the tankless water heater picks up the slack. I really want to add water storage to the mix to increase the efficiency of the OWB. I haven't figured out whether I want to add it to the radiant side which is a pressure system or the OWB which is non-pressure? Originaly I wanted to insulate and bury the water tank out next to the wood stove. Now I leaning toward putting it into the basement to heat that space as well. If I put the water storage in the basement I will probably build something in place due to the limited access of getting a propane tank down there. Oh, by the way I just purchased a 5 ton Trane open loop geothermal unit at an auction sale that I want to incorporate into the system as well. That is where I went from scratching my head a little to down right confused. Any help would be greatly appreciated.........I am also considering replacing the OWB with an Orion EKO 60 to further increase efficiancy. Will this be necessary if I incorporate the geothermal unit???