Natural Gas Pipe Sizing Calculator

For a standard Australian house with a gas cooktop, continuous flow hot water system, and a gas space heater (total load around 210 MJ/h), you will typically need a DN25 (1 inch) or DN32 (1¼ inch) copper trunk line from the gas meter, depending on the pipe run length. Short runs under 10 metres can often use DN25, but longer runs over 15 metres generally require DN32 to stay within the 0.75 kPa pressure drop limit under AS/NZS 5601.1.

Under AS/NZS 5601.1:2022, the maximum allowable pressure drop from the meter outlet to the inlet of any appliance is 0.75 kPa for standard 1.10 kPa low-pressure gas installations. This ensures that even when all appliances run simultaneously, each appliance receives at least 0.35 kPa operating pressure.

Sum the manufacturer rating plate MJ/h values for all connected gas appliances. Typical residential values: 4-burner cooktop (36 MJ/h), continuous flow hot water system (157 to 199 MJ/h), ducted gas heater (30 to 45 MJ/h), outdoor gas BBQ (25 MJ/h). Add them up to get your total main trunk load.

Yes. Multilayer PEX-AL-PEX pipe (such as Auspex Gas, Rehau, or Kembla) is approved under AS/NZS 5601.1 for above-ground and underground gas installations. However, remember that PEX-AL-PEX has a smaller internal diameter than copper for the same nominal size (e.g. DN20 PEX has ~16mm ID vs ~18.9mm ID for copper), so you may need to step up a pipe size when using PEX.

Natural gas (methane) is lighter than air (SG 0.60) and operates at 1.10 kPa meter pressure, whereas LPG (propane) is heavier than air (SG 1.52) and operates at 2.75 kPa. LPG delivers more energy per cubic metre (93.3 MJ/m³ vs 38.7 MJ/m³), meaning the flow rate and pipe sizing tables are completely different. You cannot use natural gas tables for LPG installations.

A Rinnai 26 (or Rheem Metro 26) continuous flow hot water system consumes 199 MJ/h. A 199 MJ/h load requires a minimum DN25 (1 inch) pipe for runs up to 12 metres, or DN32 for longer runs. Connecting a 199 MJ/h continuous flow unit to an existing DN15 or DN20 gas branch will cause pressure drop and burner ignition failure.

Yes. All gas fitting work in Australia must be carried out by a licensed gasfitter. It is illegal for an unlicensed person to install, alter, or repair gas piping. Upon completion, the gasfitter must test the installation for tightness and issue a Gas Compliance Certificate / Notice of Completion to the owner and energy provider.

Friction loss increases with pipe length. As gas flows through a pipe, friction against the internal pipe wall causes pressure to drop. A DN20 copper pipe can carry 56 MJ/h over 5 metres, but only 23 MJ/h over 30 metres. Longer pipe runs require larger diameters to deliver the same MJ/h load within the 0.75 kPa pressure drop budget.

Elbows, tees, valves, and bends create additional turbulence and friction loss. AS/NZS 5601.1 allows you to use an equivalent length multiplier: add +10% for simple runs with few fittings, +25% for standard domestic runs with moderate bends, or +40% for complex commercial runs with many fittings.

AS/NZS 5601.1 recommends keeping natural gas velocity below 6.0 m/s in consumer piping to prevent whistling noise, valve vibration, and excessive pressure loss across fittings.