Sizing criteria and pressure drops under BS 6891 for natural gas.
To ensure that all gas appliances operate safely and receive their full design heat input, domestic gas installation pipework must be sized correctly under BS 6891:
- Maximum Pressure Drop: The total design pressure drop between the outlet of the primary gas meter regulator and the inlet connection of any individual gas appliance must not exceed 1.0 mbar (when all appliances on the installation are running simultaneously at maximum rate).
- Impact of Excessive Drop: If pipework is undersized, the pressure drop will exceed 1.0 mbar, causing a drop in working gas pressure at the appliance. This can lead to burner flame instability, poor combustion, carbon monoxide release, or appliance lock-outs.
- Sizing Tables: Engineers use sizing charts from BS 6891 to select correct pipe diameters (typically 28 mm, 22 mm, or 15 mm copper/steel) based on flow rate (kW demand) and equivalent length of the run (including allowance for bends and fittings).
*Original revision guidance; confirm sizing criteria and gas flow calculations against BS 6891.*