sizing circulators

Bob Sweet

Yes, size the pump for the total gpm required for the entire system at the head required for the longest run. 6 gpm @ 12 ft/hd.

Bob Calabretta

sizing circulators

Hi everyone,
I have a question about sizing pumps that's been bugging me for years. I know a pump must be sized to deliver 1 gpm per 10000 BTUH(if you're looking for a 20 degree delta t). I got that. I also know to figure 6 feet of pump head per 100 ft of pipe, measuring the longest run only. I got that too. What no one ever explains to me - and maybe it's an extremely obvious thing that know one misses but me - is that when I go to a pump curve, do I size that pump for the TOTAL system flow rate at the head required for the longest run, or do I size it just for the longest run's flow rate at the head required for the longest run? Example - let's say I have 2 runs of 3/4 baseboard. They both have 50 ft. of element on them. So 50 x 600 btuh/ft x 2=60000 BTUH - each loop needs 3 gpm. But let's say 1 loop has a total length of 100 feet and the other has 200 feet. Do I size that pump to move 6 gpm at 12 ft of head or 3 gpm? Help me out - I feel terribly ignorant.

Kevin__Flynn

Pumps

Bob,

You have to deliver the entire BTU's or flow to the system but if you have enough pressure or head to overcome the most restrictive part of the system you will certainly have enough to overcome the rest.

So your answer is all the flow at the worst head, or 6 GPM at 12' of head.

Kevin Flynn