As the result of some good advice on this forum, I am replacing my current heat source (hot water tanks) with a NextGen boiler system. I have done the math and my flow and head requirements are a bit higher than the built-in pump is capable of delivering. This is not a problem, since there is a relay for a supplementary pump built into the system. However, I am a bit uncertain about how to now calibrate the flow using a second pump. Am I correct that I only need to concern myself with configuring the secondary pump so that it is able to deliver water at the needed flow rate against the system head, and that the primary pump does not enter into the overall flow calculations? Certainly, the number of gallons of water delivered by the pumps can not exceed the capabilities of either pump, but does placing two pumps in series overcome any additional head? Thanks

Where are you finding the best price on the NextGen? As soon as I have some time I'll look at this with you, if nobody else does. Do you have a schematic of your system? "Am I correct that I only need to concern myself with configuring the secondary pump so that it is able to deliver water at the needed flow rate against the system head, and that the primary pump does not enter into the overall flow calculations?" I think this assumption is correct but a diagram & your calcs would help be sure.

You need to know your system hydraulic friction head at your required flow rate to generate your required heat gain at your outdoor design condition. You can determine that by using the hydronic radiant floor heating design software on our website or some other similar software. Basically, when you place pumps in series, the heads of each pump add. When you place pumps in parallel, the flow rates of each pump add. So what you need to do depends on whether you need to generate more head or more flow rate.Yes, NextGen is a great HR appliance when an electric fuel source makes economic sense.

Thanks for the clear explanation. So, in practical terms, if I have a system that requires 4G/min at 12 feet of head, and I have two pumps each with three speeds . The best the pump can do on speed 3 is 4G/M at 10 feet of head. and on speed 2 it can pump 4G/M at 6 feet of head. Therefore I would put the two pumps in series and rum them both on speed 2, to achieve 4G/M and overcome 12 feet of head? Conversely, if speed 2 could produce 2 G/M at 12 feet of head then I could use both pumps in parallel to achieve the same thing? Additionally, if the pump can produce 4 G/M at only 2 feet of head on speed 1, I could put both pumps in series and run one on speed 1 and one on speed 3?

Yes, your thinking is indeed correct. You might want to get a couple pumps from NextGen. You could use one as your secondary and the other as a spare. In fact, you can buy a spare parts kit from NextGen that contains several other components in addition to the pump.