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Specifying ECM circ pump for 23 unit apt building with unusual heating system
The building is from 1963 and is zoned by apartment (24 zones including office). Radiation is by radiant panel. The "baseboard" is 8" tall and 3/4" thick; behind it is a simple 1/2 copper loop. Amazingly, it works amazing! The boiler room has twinned gas fired boilers and the system pump is a B&G HD3. Christmas morning, the pump stopped and we got it going with a screwdriver and some oil but I take the warning to heart and am shopping for a high-efficiency replacement pump.
Using Dan's sizing method, I am looking for 45 GPM (2" piping at the pump) and 22 Ft. of head, based on 130' to the most distant apartment plus another 50' of baseboard in that unit. (180' x 2 x 6ft head/100 ft).
So far so good. Except the dying B&G is nowhere near that output. At 45 GPM, the B&G is rated for 16' of head.
So what do you think? Should I match the B&G spec or size it for the math? Again- it's been working well for the 10 years we've owned and managed the building.
I like the Grundfos Magna3 40-80 which, at 45 GPM is just a hair under 20 ft. It gives some more oomph compared to the old B&G. Is the auto-adapt the right way to go with an old, unknown system like this? I like it over the Taco VR15-1 which appears to have a set up WAY beyond my pay grade (I'm an M.E., but not a heating professional).
Thanks for any help and happy 2017 to all!