What Size Hot Water System Do I Need?

Correctly sizing your hot water system is actually fairly important. Many people will simply install the same size system that was already there (if replacing an old system). While this may work, we always recommend evaluating your family's hot water usage to ensure that the hot water system you've chosen is the right one for your household. 

Why is the right size Hot Water System so important?

If your hot water heater is too small for your needs, you will find yourself continually run out of water. On the other hand, if your hot water system is too large for your needs, you are going to spend an unnecessary amount of energy (and therefore money) heating it. This is because your hot water system will keep maintaining the heat of your water, even when you are not using it. Your system has to work harder to keep a larger amount of water hot. So, it’s best to find a tank size that comfortably covers your needs but doesn’t go too far beyond them.

So, what size hot water system do I need?

The following tables will help you to calculate the right sized hot water system for your household. Bear in mind that the ‘peak usage’ is the rate at which water is consumed in your home at those times when hot water is most in demand (i.e. in the mornings, when the whole family showers before going to work or school).

The peak usage takes into consideration the factors noted above, such as the number of showers attached to the system, the type of shower heads used, and whether the whole family uses the hot water system within a short period of time. For example, if your whole family showers in the morning using three different showers, your peak usage will be high.

While the size of the hot water system will more than likely vary depending on your specific needs, the average 4-person Australian home will need at least a 160 litre tank for a continuous electric system, or a 250-315 litre off-peak system. If you’re in the market for a gas tank, a 4-person house averages a 170 litre tank. 270-315 litre tank should be sufficient for heat-pump users. 

Electric hot water system

Number of people Peak usage Tank size
5 – 8 High 400
Low 250
3 – 6 High 315
Low 160
2 – 4 High 160
Low 125
1 – 3 High 125
Low 80


Gas or LPG hot water system

Number of people Peak usage Tank size
5 – 8 High 340
Low 170
3 – 6 High 260
Low 160
2 – 4 High 160
Low 135
1 – 3 High 135
Low 90