Calculate Mechanical Pre-Purge Times with Absolute Compliance
The pre-purge cycle is your primary defense against start-up explosions. Guessing purge timings or relying on default Burner Management System (BMS) settings can lead to catastrophic failures and severe regulatory breaches. GasCalc instantly calculates the exact mechanical pre-purge time required to dilute and displace accumulated combustibles, ensuring your timings strictly conform to AS 3814 and AS 1375.
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Core Capabilities & Audit-Ready Reporting
Stop risking compliance failures on manual math and generic approximations. GasCalc provides indisputable mathematical proof of actual purge times in the field.
Dynamic Volume Rules
Instantly switch between the standard 5-volume change requirement and the OEM-certified 3-volume "Plug Flow" concession with a single toggle, applying the correct mathematics instantly.
25% Flow Validation
The tool automatically cross-checks your measured purge flow against the appliance's maximum commissioned airflow, instantly flagging non-compliant rates that fall below the mandatory 25% threshold.
15-Minute Guidance Warnings
Automatically alerts you if the calculated purge time exceeds 15 minutes, prompting you to evaluate fan sizing or damper positions in accordance with AS 3814 guidance.
Data-Driven Compliance
Generates a complete, JSON-driven mathematical breakdown of the purge time calculation, ready to be exported to your commissioning report.
Integrated Volume Helpers
Easily map the internal volume of the combustion chamber (Vc) and any horizontal lateral flues (Vf) using built-in rectangular and cylindrical geometry tools.
Inspector-Ready Output
Outputs crisp, vector-based PDF reports directly from the field, providing Technical Regulators with the exact mathematical proof required for Type B appliance certification.
How the Calculator Works
The Pre-Purge is a critical safety cycle. GasCalc ensures you establish the exact timing required to clear the combustion chamber and lateral flues before ignition.
Map Total Volume
Define the internal volume of the combustion chamber (Vc) and any horizontal flue sections (Vf) where gases could accumulate.
Enter Airflow Data
Input the appliance's maximum air capacity and your measured purge airflow. GasCalc ensures the purge flow meets the 25% minimum rule.
Select Purge Rule
Choose the standard 5-volume rule, or apply the 3-volume rule if you have verified OEM certification for plug flow characteristics.
Legislative Framework
State & Territory Regulations
Compliance with AS 3814 is a strict legal requirement. The mechanical pre-purge is a mandatory mathematical proof that must demonstrate adequate volume changes before ignition is attempted.
AS 3814:2018 (Clause 2.20.2.2)
Mandates that the duration of the pre-purge must ensure at least 5 volume changes. Variations down to 3 volume changes are only acceptable if satisfactory "plug flow" conditions are proven.
AS 1375:2023 (Clause 3.8.3)
Requires the flow rate of the purging medium to be not less than 25% of the maximum flow rate of the combustion air to ensure effective displacement of combustibles.
GasCalc validates all structural flow parameters before burner management timings are confirmed.
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