The Installation Volume Calculator sits in the Gas Engineer Software mobile app alongside the Gas Rate and Gas Pipe Sizing calculators.
It does two connected jobs:
Installation and purge volume: enter the pipework and meter, and it works out the volumes using the IV = IVf + IVp + IVm and PV = 1.5x IV formulas.
Tightness test check: add the pressure drop you measured, and it uses the installation volume or percetipble movement figures to tell you whether the test passes.
Where to find it
Open the Gas Engineer Software app and go to Tools & Calculators > Installation Volume Calculator.
Working out installation and purge volume
Choose the Gas type: Natural gas, LPG or LPG/air.
Enter the length in metres of each size & type of pipe.
Select the Meter: U6/G4, E6, U16, or No meter.
Use the m³ / L switch to show the results in whichever unit you prefer.
The results update as you go. You'll see:
Pipework (IVp): the internal volume of all the pipe you entered
Fittings (IVf): a 10% allowance on the pipework volume to cover elbows, tees and valves
Meter (IVm): the internal volume of the meter you selected
Installation volume (IV): the total of the three above
Purge volume (PV): 1.5 × the installation volume
Checking a tightness test
Once you've entered your pipework and meter, you can check your tightness test result in the same screen.
Choose the test type:
Existing appliances connected (the default): the permissible drop is based on your gas type and installation volume.
Pipework only / new appliances: no perceptible movement is allowed.
Enter the Observed drop in mbar from your test.
Understanding the verdict
Note: If you run a tightness test and there is no perceptible movement, it may not be necessary to calculate the installation volume, as this would be an automatic pass. However, if there is perceptible movement, IGEM/UP/1B Edition 4 requires the engineer to calculate the installation volume.
There are four possible results:
PASS (green): the observed drop for the system is 0.2 mbar or less, which is an automatic pass and counts as no perceptible movement.
Within limits — retest pipework only (amber): on an existing-appliance test, the drop is over 0.2 mbar but within the permissible drop bands for the associated installation volume. This is a pass for the whole system, but only if the drop is coming from the existing appliance. Pipework and new appliances must show no perceptible movement (a maximum of 0.2 mbar in this calculator).
Where an appliance can't be isolated, test with it connected and select the pipework only option.
FAIL (red): the drop is over the permissible drop, or over 0.2 mbar on a pipework-only test.
Outside IGEM/UP/1B scope (> 35 L): the installation is too big for this method, so no verdict is given.
Good to know
The calculator covers domestic installations using U6/G4, E6 and U16 meters, with pipe up to 35mm copper and 1¼″ steel.
IGEM/UP/1B Edition 4 allows electronic gauges reading to two decimal places to treat readings up to 0.25 mbar as no perceptible movement. To keep things simple and on the safe side, this calculator applies 0.2 mbar across the board.
The calculator is for guidance. Always follow IGEM/UP/1B Edition 4 and your own judgement on site.
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Need Help?
If you have any questions, get in touch with our support team at support@gasengineersoftware.co.uk, call us on 020 7129 7058, or use the in-app chat.