LPG Gas Pipe Sizing Calculator

For a standard residential LPG installation with a cooktop and hot water system (total load around 190 MJ/h), you will typically need a DN32 or DN40 copper main line from the regulator, depending on the pipe run length. Short runs under 10 metres might squeeze into DN32, but longer runs generally need DN40. Always check the AS/NZS 5601.1 LPG capacity tables for your specific load and distance.

LPG is 2.5 times heavier than natural gas (specific gravity 1.52 vs 0.60) and packs 2.4 times more energy per cubic metre (93.3 MJ/m³ vs 38.7 MJ/m³). LPG also runs at a higher supply pressure (2.75 kPa vs 1.05 kPa). Because of these differences, the pipe capacity lookup tables are completely different. You cannot use natural gas tables for LPG sizing.

Most homes with a cooktop and either a gas heater or gas hot water system need a dual 45kg manifold at minimum. A single 45kg bottle only supplies about 65 MJ/h continuously — not enough if your total load exceeds that. Dual bottles give you about 130 MJ/h and provide automatic changeover so you never run out mid-shower.

A stage 2 regulator is the second pressure reduction device in an LPG system. The first-stage regulator on the cylinder drops the high bottle pressure (800-1200 kPa) down to about 35 kPa. The second-stage regulator on the house wall drops it further to 2.75 kPa for delivery to household appliances. Most residential LPG installations in Australia use this two-stage setup.

Standard residential LPG pressure is 2.75 kPa at the second-stage regulator outlet. Appliances need at least 2.25 kPa at their inlet to operate properly. That leaves a 0.50 kPa pressure drop budget for the internal pipe run from the regulator to the furthest appliance.

The physical pipe materials (copper, steel, PEX-AL-PEX) are the same for both gases. However, you cannot simply swap from one gas to the other without resizing — the pipe capacity tables, regulator pressures, and appliance orifices are all different. Converting from NG to LPG requires a licensed gasfitter to recalculate pipe sizes, change regulators, and re-jet every appliance.

Frosting happens when you draw gas out of the cylinder faster than the liquid LPG can boil off. The rapid evaporation absorbs heat from the bottle wall, causing moisture in the air to freeze on the outside. It means the bottle is being asked to deliver more gas than it can handle. The fix is to add more cylinders (manifold) or upgrade to a bulk tank.

A single 45kg LPG cylinder can continuously supply about 65 MJ/h in mild weather (20°C+). In cold conditions below 5°C, this drops to about 40-50 MJ/h because the liquid propane boils off more slowly. If your total appliance load exceeds the bottle withdrawal rate, the gas pressure drops and appliances start cutting out.

Yes. All LPG gas fitting work must be carried out by a licensed gasfitter in every Australian state and territory. This includes running new pipe, connecting cylinders, fitting regulators, and commissioning appliances. A gas compliance certificate must be lodged after every installation.

Yes, PEX-AL-PEX (multilayer pipe with aluminium core) is approved for LPG installations under AS/NZS 5601.1. Make sure you use gas-rated press or push-fit fittings designed for that specific pipe brand. Note that PEX-AL-PEX has smaller internal diameters than copper, so you will often need to go up a size to carry the same MJ/h load.

AS/NZS 5601.1 sets minimum clearance distances for LPG cylinders. For cylinders up to 55kg aggregate, the minimum distance from an opening (window, door, vent) is 1 metre, and from an ignition source is 3 metres. For larger installations, the distances increase.

Medium pressure LPG runs at around 7 kPa — higher than the standard 2.75 kPa residential low pressure. It is used on rural properties with long pipe runs (30 metres or more) where the 0.50 kPa pressure budget at 2.75 kPa is not enough. With 7 kPa supply, you get a 4.25 kPa drop budget, allowing smaller pipes over longer distances.

LPG (propane) has a gross calorific value of about 50.2 MJ per kilogram. To convert from MJ/h to kg/h, divide the MJ/h rating by 50.2. For example, a 157 MJ/h instantaneous hot water system uses about 3.1 kg/h of LPG. This is useful when checking cylinder discharge rate limits.

No. Bulk LPG tank installations (190kg and above) must be carried out by a licensed gasfitter and approved by your LPG supplier (Elgas, Origin, Kleenheat, Supagas, etc.). The supplier handles installation, testing, and compliance.

An undersized LPG pipe causes a pressure drop greater than 0.50 kPa at the appliance inlet. The symptoms are appliances cutting out on error codes, yellow or lazy flames on cooktops, hot water systems failing to ignite, and gas heaters running below rated output.