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Apartment living: How your water is heated and charged.

Learn more about the centralised hot water system in your apartment.


If you live in an apartment, you may not be aware how your water is being heated—it can be a bit different to the average Aussie abode.

In Australia, hot water heaters are usually the second-largest energy users out of all the appliances in your home*, so it’s useful to understand how they work. If you live in an apartment complex, your hot water is either heated by electricity, solar or natural gas.

If your complex uses a centralised system, you may have heard the term ‘centralised hot water’ or ‘community hot water’, but this doesn’t mean there’s a big pool of water for you to go wild with hour-long showers.

We’re here to empower you to understand and manage your own energy, and in turn, waste less and save more on your next energy bill.

It all starts with a boiler

There is no one-size-fits-all solution for hot water systems. Depending on the size of your apartment complex, there may be one or more centralised boilers. When you turn on the tap, a boiler (powered by natural gas) heats your water, and it travels through a network of pipes until it reaches your apartment. Thank you, distant boiler! 

Finding your meters and master data loggers

A centralised system saves you from a hot water tank taking up valuable space in your apartment, but you will still have a hot water meter that measures your usage within your apartment. 

Not sure where your hot water meter is? You might find it hiding under your kitchen sink, in the bathroom manhole or in a common area of the apartment complex. If in doubt, you can always ask your Body Corporate or Owners Corporation.

Reading your meter is easier than you think

When you find it, you can read your meter yourself. Firstly:

One unit on your hot water meter is equal to 10 litres of hot water used.

On most meters, the black numbers measure whole units and the red numbers track the decimal places.

For most gas hot water systems, the volume of hot water used by each apartment is registered by its gas hot water meter and sent to a master data logger. Meter data providers visit the apartment complex every 90 days or so to read the master data logger and send each apartment’s hot water meter reading to ActewAGL (or your energy retailer).

Common factor

If this is your first time living in an apartment with centralised hot water, your gas bill will be slightly different to what you’re used to. Your apartment bill is calculated by:

The total amount of gas used by the apartment complex to heat water, divided by the total amount of hot water used. 

This handy calculation determines the amount of gas (in megajoules) used to heat each litre of water. The result is known as the common factor.

Every apartment complex is different—and your common factor is unique too. 

Along with your apartment’s daily usage, there are a variety of other things that can make your complex’s common factor higher or lower. Sometimes heat is lost as the hot water travels through the pipes, or it may take extra energy to heat water on a very cold day, as opposed to a hot day. These factors, as well as the occupancy rate of your complex, the system’s efficiency and maintenance and any heating augmentation being used, such as solar or cogeneration, will also affect your common factor.

To calculate the total amount of gas you’ve used to heat the water in your apartment, the reading for your apartment is multiplied by the common factor. You’ll only ever pay for what you’ve used.

Say hello to a more energy-efficient you

In a typical household, 75% of hot water is used for showers. If you’re looking for more ways to reduce your energy use and save on your energy bills, your shower is a good place to start—and you’re probably using a lot more water than you realise. Run your shower into a bucket for 15 seconds, measure the water and multiply by four to get your shower flow rate per minute. If it’s more than nine litres per minute, it’s time to switch up your shower head to something more efficient. By upgrading to water-efficient appliances and fixtures, the average household could save up to 65% from avoided water heating costs^.

See a visual representation of what your apartment’s centralised hot water system might look like, take a look at our Gas hot water fact sheet.

Take charge of your energy—learn more about meters and how to read them.

Find more ways to reduce your energy use and save on your energy bills—check out our energy-saving tips, made for the capital region.

Looking for more information about your centralised gas hot water system? Ask your Body Corporate or Owners Corporation, or have a chat to your local ActewAGL Energy Consultant on
13 14 93.


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