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Low flow circulating pump vs high flow circulating pump

I have two 150 HP Scotch Marine hydraulic boilers with a recirculating line off the header manifold and returning back to the return manifold (for circulation through the boiler) (1725 RPM, 1/2 HP, 120 V). Then I have a water to water heat exchanger for domestic hot water with a circulator (1725 RPM, 3/4 HP, 208 V) circulating the hydraulic water through the exchanger. I also have a 1600 gal domestic hot water storage tank with a circulator pulling cold water off the bottom going through the exchanger returning to the bottom of the storage tank (the hot water return has a reverse dip tube going haft way up into the tank).

My question is the circulator (1725 RPM, 3/4 HP, 208 V) circulating the hydraulic water through the exchanger should this be a low flow or high flow pump?


  • Jamie Hall
    Jamie Hall Member Posts: 17,065
    It's all in the delta T's across the heat exchanger, and how the heat exchanger is piped. If the heat exchanger is counterflow, you can run a much higher delta T across it (if you want to) than if it is parallel flow.

    That said, your circulator within the restriction above -- will govern the delta T. High flow, low delta T. Low flow, high delta T. Adjust the flow to get the output temperature you want...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England