Every family and home is different, so choosing the right size hot water system to install for your needs can save you money and disappointment.

Choosing the Right Fit: Hot Water Unit Size Explained in Our FAQ

In our FAQ on hot water unit sizing, Australian Hot Water addresses the common queries surrounding the crucial decision of choosing the right-sized hot water unit for your needs. We understand that finding the optimal size is essential for efficiency and cost-effectiveness. This comprehensive guide walks you through considerations such as household size, usage patterns and available space, helping you make an informed decision. Whether you’re opting for a compact hot water unit for a small apartment or a larger system for a family home, our FAQ provides valuable insights to ensure you find the perfect fit. Trust Australian Hot Water to demystify the process of determining hot water unit size, making your selection process a seamless and informed experience.

Why the right size is important?

The main two reasons why correctly sizing your hot water heater is important.

1) Running out of hot water: If your hot water tank is too small for your needs, you will continually run out of water. 

2) Increased costs: If your hot water system is too large for your needs, the system will continue maintaining the heat 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.

What Hot Water System Sizes Are Available?

Hot water heater sizes start at around 25L and go up to around 400L. It’s not simply a case of saying X number litres per family member. There are a number of important factors to consider. So, check out this comprehensive guide to help you decide what size hot water heater is right for you and your family.

Factors to Consider when sizing a Hot Water Systemhot water tank

When deciding what size hot water heater is right for your needs, the following factors will need to be taken into account:

  1. How many people will be using the hot water heater?
    • You should obviously count the number of people living in your home full time, but also consider how often you have visitors, such as relatives coming to stay.
  2. How many showers or other outlets will the heater be attached to?
    • If you only have one shower attached to your hot water heater, then the heater may have more time to heat more water for subsequent showers, which means a smaller heater may be suitable.
    • If, however, the heater needs to service a number of bathrooms at the same time, it will need to have a larger amount of water initially on demand.
  3. The water usage habits of your family.
    • You should consider things such as whether your family takes long showers, but also at what times of the day your family uses hot water.
    • For example, if everyone in your family showers in the morning, you may need a larger water tank than if some showered in the morning and some in the evening.
  4. The type of shower heads you use in your bathrooms.
    • A shower head can have a big impact on your hot water consumption.
    • This includes both the size of the head and the pressure at which it passes water.
    • Some shower heads are water-saving, which will significantly reduce the demand on your hot water system.
  5. Gas or electric?
    • Whether you choose a gas or electric system will have an impact on how large the tank will need to be – read on to find out how.
  6. Do you use a Dishwasher?
    • The number of cycles your dishwasher uses and they times of day used should be calculated 
  7. Do you use hot water in your washing machine cycle?
    •   Washing machines use large amounts of water particularly if they have a large tub/drum or have a low water rating.

Does Peak or Off Peak Power Matter?

Keeping the costs of running a hot water heater down will depend on whether your system is connected to a peak or off-peak tariff (often between 10 pm and 7 am). If connected to an off-peak tariff you’ll need to install a larger system so it can supply hot water to your home for the whole day and reheat only at night (during the off-peak times).

This applies to solar hot water systems as well as they only heat water during the day (without the booster function).

Does Gas or Electric Make a Difference?

Whether your hot water system is powered by electricity or natural gas will make a significant difference to the size of the tank you will need.

Gas hot water systems are able to heat their tanks at a faster rate. This means that, generally, the system can heat new water entering the tank quickly enough to service hot water outlets soon after water has been taken from the tank. An electric system, by contrast, needs to have greater reserves of pre-heated water to service hot water outlets when demand is high.

However, a small gas system will not be able to provide the same number of hot showers if they are all taken at the same time (for example if three or four bathrooms are used at once).

Another thing to consider is that gas systems are generally cheaper to run than electric systems. You might therefore be able to save yourself some money by buying a smaller (and therefore cheaper) gas system that is also kinder to your energy bill over the longer term. However, you also need to check that your home has an available gas supply or can be connected to the natural gas grid.

What size hot water system do I need?

The following tables will give you a rough idea of how to calculate the right sized tank for you and your family. 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.

Electric hot water system

Number of peoplePeak usageTank size
5 – 8High400
3 – 6High315
2 – 4High160
1 – 3High125

Gas or LPG hot water system

Number of peoplePeak usageTank size
5 – 8High340
3 – 6High260
2 – 4High160
1 – 3High135
Dux hot water systems are available through your local, authorised agents here at Australian Hot Water

How to make the right decision

Once analyzing the above factors you should be able to come to a well-grounded decision about which size hot water system is best going to suit your needs and save you money in terms of efficiency.

Still have questions? Speak to a hot water plumber near you to get professional advice specific to your requirements.



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