IGEM/UP/1B Edition 4 Tightness Test Calculator
Edition 4 became mandatory on 1 October 2026, and Edition 3 is now withdrawn. Permissible drops are now set by the Installation Volume (IV), not by meter size alone. Enter the pipework and meter to get the IV, the maximum permissible drop and the purge volume.
Edition 4 permissible limits
| Fuel gas | Installation volume (m³) | Max permissible drop (mbar) |
|---|---|---|
| Natural gas (Table 3) | ≤ 0.005 | 8 |
| > 0.005 to ≤ 0.010 | 4 | |
| > 0.010 to ≤ 0.015 | 2.5 | |
| > 0.015 to ≤ 0.035 | 1 | |
| LPG/Air (Table 2) | ≤ 0.025 | 1.5 |
| > 0.025 to ≤ 0.035 | 0.5 | |
| LPG (Table 5) | ≤ 0.0025 | 2 |
| > 0.0025 to ≤ 0.005 | 1 | |
| > 0.005 to ≤ 0.01 | 0.5 | |
| > 0.01 to ≤ 0.035 | No perceptible movement |
Scope of IGEM/UP/1B Edition 4
- Installation volume 0.035 m³ or less (including the meter)
- Pipework 35 mm nominal bore (DN32, R1¼) or less
- Not covered: boats and LPG service pipework
- Meter badged capacity 16 m³/h or less
- NG and LPG/Air: 21 mbar or less nominal operating pressure at the meter outlet. LPG: 37 mbar or less at the final-stage regulator outlet
Anything larger is tested to IGEM/UP/1 or IGEM/UP/1A.
Test procedure overview
- Do a visual inspection. Set appliances up for the test: cooker lids up, permanent pilots out.
- Turn off the ECV or other appropriate valve and connect the gauge.
- Do a let-by test at 7–10 mbar for 1 minute.
- Raise the pressure to the tightness test pressure for the fuel gas and let the temperature stabilise for 1 minute. For natural gas this is 20 mbar. If 20 mbar cannot be reached, 18 mbar is the minimum, and a pass at 18 mbar needs operating pressure checks to IGEM/G/13.
- Adjust the pressure if needed, then test for a further 2 minutes.
- For pipework only, new appliances only, or appliances that cannot be isolated, there must be no perceptible movement.
- With existing appliances, if the gauge moves, calculate the IV and compare the drop with the table above.
- If the drop is within limits, isolate all appliances and retest the pipework only. Any perceptible movement is a fail.
- Reintroduce gas, then test disturbed joints and the pipework between each isolation valve and its appliance with LDF. There must be no smell of gas.
No perceptible movement means ≤ 0.25 mbar on a water gauge or a 2-decimal-place electronic gauge, and ≤ 0.2 mbar on an electronic gauge that reads to 1 decimal place.
This calculator is a guide for Gas Safe registered engineers. It does not replace IGEM/UP/1B Edition 4. Use the manufacturer's meter volume where you have it, and the calculated fittings volume where you can work it out, with 10% of the pipe volume as the fallback. Stainless and CSST use the steel figure for the same size. Permissible limits are from IGEM/UP/1B Ed 4, as summarised in Gas Safe Register ISU 133 (Edition 2, April 2026). You are responsible for applying the full standard.