Fred61, You and I may have made the same mistake. I, too, installed a Radiant Floor. I have an open system so that my potable water runs through the slab before it is used in the house. Should I convert to a closed system if i use the boiler? I never really understood why we hooked up the water the way the Radiant Floor guys asked us to, so maybe this is a dumb question, but why wouldn't a simple closed system (with expansion tank) work best in this case? It seems like a quick and simple conversion. I have the Radiant Floor installation diagrams to reference if needed. (they are also available online).
I have the red PEX that I think is rated to at least 100 PSI. I don't know the input temperature of the water in the propane-fired system but I am assuming I could mix cold water into the pipes to make the boiler output exactly what it needs to be to work in my system.
About that "smaller, less expensive" comment, I would like to minimize my additional cost. How many gallons of water (or maybe I should say "What size boiler") should I be looking for if I have 2,500' of 3/4" PEX in my slab? I won't make the change if it means I have to buy a $5K boiler. I hope there is a cheaper solution, especially since I have already invested so much into the PEX and Radiant Floor.
General info because someone asked - I live in South Central Tennessee. The house is 5,400 sq. ft. but I am only trying to solve the heating problem for the 1st floor which is about 2,500 sq. ft.
I'm encouraged to continue my search. Thanks for all of the good info so far!