Dear Mark, first, pull up www.rpa-info.com this is the website of the radiant panel association. Their phone # is 970 613 0100. They are a mine of information on hydronic heating, designers, installers and equipment suppliers. I recommend that you don't install an indirect fired water heater, it will only complicate your installation and drive up the cost. Call Keith Kelley at Radiant Concepts, 651 452 2025, he will design your system from your floor plan and you install it, it saves a bunch. Then you get your separate tankless waterheater from me, I supply electric or gas. 800 851 9891. Good luck. Cheers, Brian.