Circulator Pump Sizing Calculator

Estimate required flow rate (GPM) and total dynamic head (TDH) to select the right circulator pump for a hydronic heating or cooling system.

Flow rate (GPM)

System heating/cooling load (BTU/hr) From boiler output or load calc

Design temperature drop (ΔT, °F) Typically 20°F for hydronic heating

Head loss (feet of head)

Total equivalent pipe length (ft) Longest circuit, supply + return, incl. fittings

Piping friction assumption Ft head loss per 100 ft equivalent

Boiler pressure drop (ft head) From boiler spec sheet, if known

Additional component drop (ft head) Coils, zone valves, heat exchangers, etc.

Enter valid numbers for all fields.

Recommended pump operating point

Piping head loss

Boiler + component head loss

required flow (GPM)

total dynamic head (ft)

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GPM is calculated using the standard hydronic formula GPM = BTU/hr ÷ (500 × ΔT). Head loss uses simplified friction-per-100ft assumptions rather than a full pipe-by-pipe friction loss calculation. Use the resulting GPM and TDH operating point to select a pump from the manufacturer's published pump curve. For critical or large commercial systems, verify sizing with a qualified engineer using detailed friction loss tables (e.g. Bell & Gossett System Syzer).