The contractor would tell me the length of the longest (highest-pressure-drop) circuit, and that would give me the two things I'd need to size the circulator over the phone - flow and head. If he didn't know the longest circuit because all the pipes were hidden behind the walls and ceilings, I'd have him go outside and measure the length, width and height of the building. Then I'd imagine the longest run of pipe that I could put in that building.
I'd go from the left-hand corner of the building to the far end, then up to the top, across the top to the other side, down that side, back to the right-hand corner of the building, and finally, back to where I was standing. I'd base my pump head on that worst-case run, and then I'd select it from the pump curves in the manufacturer's catalog. And if my point of operation fell between a pump that was larger and one that was smaller, I would always pick the smaller one.
I did this for the 19 years I worked for the rep and I never once got a pump back. Was I oversizing? Not at all! I was sizing based on the existing piping on the job, pipe that someone else had sized based on the heat-loss of the building. I figured that if the pipes were the wrong size, someone probably would have noticed that long before the pump I was replacing had failed.
It's a simple method, based on common sense, and it works.
Respectfully,
Dan Holohan
"Plumbers Protect The Health Of The World."
