Hydronic Flow Rate (GPM) Calculator

Water flow needed to move a heat load at a chosen ΔT.

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Formula

GPM = BTU/h ÷ (500 × ΔT)

Example calculation

100,000 BTU/h at 20 °F ΔT → 10 GPM.

Practical HVAC use

Pump selection and circuit balancing.

Common mistakes

Using 500 for glycol without correction.

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Educational tool. Results are estimates from the stated formulas; always confirm with manufacturer data and the code adopted in your jurisdiction. All calculators