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Tightness Testing & Purging Guide
Tightness Testing & Purging Calculator
IGEM/UP/1B Edition 4 — Natural Gas & LPG
Easy Gas Engineer — Build 2026-08-12
Before you start: Tap ? (bottom right) to read the full guide. References shown in blue (e.g. Section 5.3, Table 3) refer to sections, tables, and figures within IGEM/UP/1B Edition 4.
✎Job & Site Details▾
⚙Test Medium▾
Select the test medium before proceeding. This determines which test procedure is used.
New installations only (Appendix 3): This procedure is for tightness testing a new installation with air before it is connected to a live gas supply. Once connected to a live gas supply, the installation shall be tightness tested with fuel gas (Section 5) and purged (Section 6) before being put into service. This air test does not replace the full tightness test and purge with fuel gas.
1Fuel Type, Gauge & TTP▾
The fuel gas that will supply this installation once connected
Determines NPM threshold (Section 4.2.1)
2Visual Inspection & Setup▾
3Stabilisation & Test▾
Step (d) — Stabilisation — 1 minute
Stabilisation timer — 1 minute
1:00
If not at TTP, re-adjust and allow further time to stabilise. Turn off pressure source.
Step (e) — Tightness Test — 2 minutes
TTP at commencement of 2-minute test
Tightness test timer — 2 minutes
2:00
4After Test▾
Once connected to a live gas supply: The installation shall be tightness tested with fuel gas (Section 5) and purged (Section 6) before being put into service. Use this calculator in Fuel gas mode to carry out the fuel gas tightness test and purge.
✎Notes▾
✎Declaration & Sign-off▾
I confirm that the air tightness test has been carried out in accordance with IGEM/UP/1B Edition 4 Appendix 3, that the results recorded are accurate, and that the installation has been left in a safe condition. I understand that this installation must be tightness tested with fuel gas and purged before being put into service.
Sign above
Disclaimer: This tool is provided as an aid to assist competent persons in calculating tightness testing parameters and purge volumes for domestic gas installations. It does not constitute engineering certification, a gas safety inspection, or a substitute for professional judgement. Users must be Gas Safe registered and competent for the category of work being undertaken. Users are responsible for verifying all calculations and ensuring all work is carried out in accordance with IGEM/UP/1B Edition 4, GS(I&U)R 1998 (as amended), and all other applicable legislation and standards. To the fullest extent permitted by law, the author accepts no liability for any error, omission, or any direct or indirect loss or damage arising from use of this tool or reliance on its output.
Confirm the installation falls within IGEM/UP/1B Edition 4 scope (Section 2).
From meter badge plate
NG: 21. Propane: 37. Butane: 28
Affects TTP — see Figures 13–16
BInstallation Volume (IV)▾
IV = IVm + IVp + IVf (Appendix 7)
Meter Volume (IVm)
Pipework Volume (IVp) — Table 8
Pipe size & material
Length (m)
Vol (m³)
Fittings Volume (IVf)
CTightness Test▾
Based on Section 5. Select gauge type first, then record test readings.
Test Equipment (Section 4)
Determines NPM threshold (Section 4.2.1)
Electronic gauges shall be calibrated at least every 12 months
Step (a) — Visual Inspection
Step (b) — Turn Off Supply Control Valve
Step (c) — Connect Pressure Gauge
Step (d) — Let-by Test — 1 minute
Should be between 7 and 10 mbar. Close valve and note reading.
Let-by timer — 1 minute
1:00
No perceptible movement (rise or fall) = pass
Step (e) — Raise to TTP
Step (f) — Stabilisation — 1 minute
Record pressure after raising to TTP and turning off supply
Stabilisation timer — 1 minute
1:00
If not at TTP, re-adjust and allow further time to stabilise
Step (g) — Tightness Test — 2 minutes
TTP at commencement of 2-minute test
Tightness test timer — 2 minutes
2:00
Record gauge reading at end of 2-minute test
Auto-calculated
Retest — Pipework Only (Appliances Isolated)
Steps (h–k) — After Test
DDirect Purging▾
Section 6. Required for new installations, after exposure to air, or where air may have entered.
✎Notes & Observations▾
Record any additional observations, deviations from procedure, details of faults found, or remedial work carried out.
✓Summary▾
✎Declaration & Sign-off▾
I confirm that the tightness test and/or purge has been carried out in accordance with IGEM/UP/1B Edition 4 and the Gas Safety (Installation and Use) Regulations 1998 (as amended), that the results recorded are accurate, and that the system has been left in a safe condition.
Sign above
Disclaimer: This tool is provided as an aid to assist competent persons in calculating tightness testing parameters and purge volumes for domestic gas installations. It does not constitute engineering certification, a gas safety inspection, or a substitute for professional judgement. Users must be Gas Safe registered and competent for the category of work being undertaken. Users are responsible for verifying all calculations and ensuring all work is carried out in accordance with IGEM/UP/1B Edition 4, GS(I&U)R 1998 (as amended), and all other applicable legislation and standards. To the fullest extent permitted by law, the author accepts no liability for any error, omission, or any direct or indirect loss or damage arising from use of this tool or reliance on its output.