Mechanical
Pipe Sizing Calculator
Estimate heating pipe size from either heat load and temperature difference or known flow rate.
Use this calculator for quick heating pipe sizing checks based on a target maximum velocity. You can size pipework either from heat load and design temperature difference, or directly from a known flow rate.
Inputs
Pipe selection is based on the smallest listed pipe size that keeps calculated velocity at or below the selected maximum.
Result
Method
Pipe size is selected by comparing the design flow rate against the internal flow area of each listed pipe size.
Internal pipe area is determined from:
Where heat load is used as the input, flow rate is first calculated from:
- v = water velocity in pipe (m/s)
- Q = volumetric flow rate (m³/s)
- A = internal pipe area (m²)
- d = internal pipe diameter (m)
- The smallest listed pipe size with velocity at or below the target is selected.
- Calculated result = -
Reference
- This calculator applies standard heating pipe sizing logic by determining design flow rate and comparing it against listed pipe internal diameters.
- Velocity-based selection reflects typical UK building services design practice for preliminary heating pipe sizing.
- Relevant guidance may include CIBSE Guide B and CIBSE Guide C for heating system design, pipework distribution and hydraulic considerations.
- Where applicable, final design should also align with relevant British Standards, project specifications and manufacturer requirements.