HTHOMETALLYTHE PRACTICAL HOME GUIDE

Heating/ CALCULATOR

Hydronic heating flow rate

Convert a heating load and design supply-return temperature difference into a water-flow estimate.

Use the heat that the water circuit must carry at the selected condition.
Use the circuit supply temperature, not the heat-source nameplate maximum.
Use the intended return temperature at the same design condition.
Use only circuits intended to operate together; equal flow is a simplifying assumption.
Supply-return temperature difference

10.0 °C

Required total water flow

14.3 L/min

Required total water flow

860 L/h

Average flow per equal circuit

2.9 L/min

Interpretation:At the entered temperature difference, the system needs about 14.33 L/min in total and 2.87 L/min per equal active circuit. Pump head and balancing still require a hydraulic design.

Water at approximately 1 kg/L with specific heat 4.186 kJ/(kg·K), steady heat transfer and equal circuit flow. Glycol, changing water properties, emitter output, control behaviour, pipe loss, valve authority, hydraulic resistance, pump head and balancing are excluded. Use a qualified hydronic design for equipment selection.

FROM ESTIMATE TO ACTION

Use the result, not just the number.

01

Verify the inputs

Measure or document each input. If a value is only an estimate, record its source and test a conservative alternative.

02

Keep the calculation traceable

Save the input link or copied result together with the date, units and assumptions. A number without its inputs cannot be checked later.

03

Confirm the decision

Compare the estimate with the related guide, current product data and requirements that apply at your location before buying or building.

Inputs to verify

Design heat delivered to water (kW)
Use the heat that the water circuit must carry at the selected condition.
Design supply temperature (°C)
Use the circuit supply temperature, not the heat-source nameplate maximum.
Design return temperature (°C)
Use the intended return temperature at the same design condition.
Active equal-flow circuits (circuits)
Use only circuits intended to operate together; equal flow is a simplifying assumption.

Continue your calculation

Heating

Radiator output at lower water temperature

Estimate how a radiator’s published heat output changes at a different supply, return and room temperature.