Circulator Pump Sizing

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Minister of Fire
Mar 1, 2012
Central Ohio
I bought a Heatmaster G4000 and I'm trying to figure out what circulator I need. Earlier this year my dealer told me a I needed a Grundfos 26-99 circulator, and then a few days ago he told me to get a B&G NBF-22. Apples and oranges. I asked him how he chooses his circulators for the installs he does and he told me he goes based it off of the distance of the piping from the boiler to the house. That doesn't compute with my German engineer brain.

What I know:

48k BTU/hr is roughly needed to heat my house on a 0 degree day
19x20 Water to Air HX - don't know the PSI drop. I could call and ask if it's a huge deal
Roughly 180 total of 1" PEX ( outside and inside )
8 - 90 degree elbows

What I think I know:

1 GPM = 10,000 BTU/hr - I'll need 5GPM
One 90 degree elbow adds 10 feet of head - 80 additional feet of head
Pressure drop on 1" PEX at 5GPM is 1.58 PSI

300 feet at 5 gpm - using 300ft since I don't know the pressure drop across the HX
1.58PSI(per 100ft 1" pex) x 3 = 4.74 psi loss
4.74 x 2.3 = 10.902 head loss
1 psi = 2.3 ft of head

Based off of my calculations I look to be in the sweet spot for a Grundfos 15-55FR. Is the Alpha2 worth $100 over the Alpha1 ? I do like the summer feature of the Alpha2 though.