I'm using a Rinnai for a snow melt. First time. Can't seem to trick it to stay on. I've got about 900 ft. of 1/2" tubing. I'm using a Grundfos 1/25 and I'm going to try the 1/6 (high head) next. Should it be on the supply or the return side? I get different answers from the reps. What about an expansion tank (also different answers).