Add your appliances, set the run lengths, and the tool sizes every segment. Branching, cumulative loads, and pipe sizing — all from AS/NZS 5601.1.
When switching from a storage hot water unit to an instantaneous system — or adding any new gas appliance to an existing line — you need to check whether the current pipe can carry the extra load. This is the first thing a gas inspector asks about and the thing most commonly missed when writing a quote.
The calculator looks up the maximum flow rate for your pipe size, material, length, and supply pressure using AS/NZS 5601.1 Tables F6 (copper, standard residential) and F9 (higher pressure). It adds a 20% fittings allowance to the measured run automatically. If the existing pipe can't handle the new demand, it shows you the minimum size to upsize to.
Use this when quoting a hot water upgrade from storage to instantaneous, when adding a gas cooktop or space heater to an existing line, or any time a customer asks whether the existing gas line can handle it. The result gives you the answer and the standard reference to back it up.