Installation and purge volumes

A) Pipe volume

Survey the whole section being calculated, including existing pipework and any new extension. Enter only the sizes used and leave unused fields blank. For inaccessible pipework with unknown lengths of different sizes, use the largest visible diameter for the maximum length (Appendix 7). Inputs support up to eight decimal places.

Copper

Steel / stainless steel / pliable corrugated stainless steel

PE SDR11

Other or unlisted pipework

Use only where the pipe volume has been calculated from reliable internal dimensions or manufacturer data.

B) Valves and fittings volume

Actual component volume comes first. Use the 10% fallback only where that additional volume cannot be calculated.

C) Meter Volume

D) Gas type and tightness-test context

If the initial test has no perceptible movement and no smell of gas, the appliance-isolation retest is not triggered by pressure loss. Where perceptible loss is observed, the allowance applies only to existing appliances after the meter and pipework have been proved gas tight. A new section must meet the no-perceptible-movement criterion.

E) Gas-smell and investigation checks

Check with the occupier where relevant. Select the escape-investigation route for any known or suspected escape, including an installation isolated following a report. A pressure-drop allowance cannot override a smell of gas. A known or suspected escape investigation requires no perceptible movement and no smell of gas (Section 5.5). Follow the applicable gas escape and unsafe-situations procedures.

Interpret “no perceptible movement” using the standard and your gauge: at most 0.25 mbar, or 0.2 mbar on an electronic gauge reading to one decimal place. This calculator does not assess gauge readings or replace the complete test procedure.

F) Scope confirmation

This calculator is limited to qualifying small installations within the published IGEM/UP/1B limits. Apart from the installation volume, which the calculator determines, confirm the gas, installation type, pipe size, meter capacity and pressure limits in Section 2.2. This includes nominal bore no greater than 35 mm (DN32), meter capacity no greater than 16 m³/h, and the applicable supply and operating pressure limits. Boats and LPG service pipework are excluded; legacy medium-pressure arrangements without a meter inlet valve need the separate Appendix 4 guidance.