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 (see question 3 for more information on how your usage is calculated and billed).
2. How do I know if I have centralised hot water billing?
You will 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.
Understanding your bill
3. What is the common factor?
So your gas hot water usage can be calculated, the common factor is used to determine the amount of gas (in mega joules) required to heat a litre of water. It is 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. The common factor is provided to AGL by your distributor who is responsible for reading the master meters (these meters are the ones common to the entire apartment block).
4. Why do you multiply my usage by 10 as well as the common factor?
[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).
So in order 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).
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
5. How do I read my 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 will be able to determine what your water usage is for that amount of time.