Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Primary/secondary and GPM on a circuit

TomTA Member Posts: 20
I was reading “Pumping away” (very interesting book) but one of the many things that still confuses me is the GPM flow over a circuit. The example in the book that prompted this question had a primary/secondary setup. The primary flows 14 gpm, and there are 3 secondary circuits which demand 3, 3, and 8 gpm each, for a total of 14. The GPM flow of each secondary circuit is calculated based on the emitter size and temperature drop (I assume). What I don’t understand is how do you LIMIT that circuit to 3 gpm (or do you?). Do you add enough restrictions to the circuit so that the pump curve puts flow at 3 gpm? I can’t imagine intentionally setting up an energy waste like that. Or is the 3 GPM the “effective flow” in terms of heat loss; that instead of flowing 3 GPM with a 20 degree heat drop, it might be flowing 6 gpm with a 10 degree heat drop. You just let the pump push through whatever it wants/can, and the emitter size will strip off the appropriate level of BTUs?


  • Zman
    Zman Member Posts: 7,446
    I think you do understand it. The output of the radiator will not be exactly linear with the flow but, close enough.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein