Kids, don't try this at home! I know it's outrageous, beyond the pale, ridiculous, absolutely insane....... But making it was a lot of fun, and I appreciate all the design help and advice that everyone offered. This is two heat exchangers. The one on the bottom is for heat storage; the one on the top for recovery. In total, there's 110 feet of 1/2-inch copper in each hx, and approximately 60 feet of 1". The storage hx has 1" and 3/4" connections so that I can dump the entire output of the boiler into the tank in the summer. Hopefully. All pressure tested with water and no leaks, of course. Well, OK, there were two fitting connections that I forgot to solder, and they leaked. Next weekend it goes into the tank.