Hot water billing basics

Centralised hot water billing: how it works

Centralised (or bulk) hot water systems are common in apartments and multiple residencies. Each residence will have an individual hot water meter connected to a central hot water system. Customers with centralised hot water are billed for the volume of gas used to heat the water based on the usage recorded by their individual hot water meter.

Identifying centralised hot water billing

You'll have an individual water meter for your apartment and a central gas hot water system for the apartment block or units. More information is available from your Body Corporate or Owners Corporation.

Understand your bill

The Common Factor

We use The Common Factor to calculate your gas hot water usage by determining the amount of gas (in mega joules) required to heat a litre of water. It’s calculated by dividing the total amount of gas used to heat the water (MJ) by the total amount of water (L) used as recorded by the central hot water system.

Usage calculations

Information for NSW customers only excluding residents of Wagga Wagga and Tamworth

If you live in NSW, you may notice that your usage has been multiplied by 10, as well as The Common Factor - this is because the hot water meter measures your usage in decalitre (a metric unit of capacity equal to 10 litres).

The Common Factor is provided to us by your distributor who is responsible for reading the master meters (these meters are the ones common to the entire apartment block).

To calculate your bill, we multiply your individual usage by 10 to determine your usage in litres, and then by The Common Factor (as The Common Factor is the amount of gas required to heat a litre of water).

For example:

Your Meter Reading = 1111 dl (x10)

Your Meter Reading in Litres = 11110

Gas usage of all units = 57544 MJ

Water usage of all units = 126190 litres

Common Factor = 57544 / 126190 = 0.4560107 rounded to 0.456011

Energy (MJ) = 1111 x 10 x 0.456011 = 5066.28 rounded to 5066 MJ

Monitoring your usage

How to read your meter

On most hot water meters, you’ll see a series of numbers. The black numbers measure whole units and the red numbers measure decimals.

By reading the meter at two different points in time (such as at the beginning of the day and at the end) you can determine what your water usage is for that amount of time. Learn more about How to read your meter.

For information on how to save on your gas bill visit Energy saving tips.

Related topics

Read your energy bill

Understand your energy bill

Read your own meter

Fees and charges on your energy bill