Plan to keep the existing boiler and cast iron radiators in service until I see how this goes. I've read about people using domestic hot water heaters or tankless boilers. The floors are 3/4" pine tongue and groove, only. So I think the radiant pex will go right through, and I can get to 3/4 of the first floor right from the cellar. Any suggestions regarding the heat source? The gas line is easily accessible in the cellar where it's going.