Where to start.. I've built my boiler out of 1/4 m.s. and I'm just about to the setting out side point of the build. I designed it to hold about 180 gallons water. I think I'm getting lost when I'm reading about total head pressure. Being a sheetmetal worker by trade, hydronics is kind of French to me. I've bought a 18x20 coil that's supposed to be good for 137,000 btus at 15gpm. I've ran 2-3/4"4supply and return lines to the house that's about 150' of pipe one way. I put foam insulation on all the line and ran them in 6" corrugated pipe about 30" or so down. Would I be better off if I made it a closed loop system? I'm from central Indiana so our winters don't get to bad for the most part. I appreciate any insight on how I can calculate everything.