Heating & Chilled Water Pipe Size Calculator

Turn a heat load into a pipe size in seconds. Enter the load in kW and the flow/return temperature difference; the calculator works out the water flow and shows every pipe size with its velocity and friction loss, highlighting the smallest one that stays within the friction and velocity limits.

How to use it

1. Enter the heat (or cooling) load carried by the pipe section and the design ΔT — for example 20 K for 70/50 °C radiators, 5 K for 7/12 °C chilled water.
2. Choose the water temperature and the pipe material.
3. Keep the default 200 Pa/m limit for distribution pipework, or lower it for quiet or long index circuits.
4. Size each section along the index circuit, then add fittings and terminal losses to get the pump head.

Step-by-step guides

• Heating Pipe Sizing: Flow, Velocity, Pa/m and Pump Head
• Heat Loss Calculation Step by Step: EN 12831 Worked Example

More free tools

• MEP Unit Converter — kW, BTU/h, TR, CFM, L/s, bar, psi
• Ventilation & Air Change Calculator (ACH ↔ m³/h)
• All free MEP calculators
• MEP Library

Results are for preliminary design and checking. Always confirm against the standard edition and local regulations that apply to your project.