What size hot water system do you need for your Perth home?

8th September, 2023

When it comes to hot water systems, size truly does matter—despite what your friends might have you believe. We reckon there’s nothing worse than starting your day off with a shower that turns from satisfying steam-room to bone-chilling bleakness in an instant. Choosing the right size hot water system for your specific needs is the best way to avoid that dreaded morning shock – but there’s more to choosing your hot water system than just tank size. From replenishment rate to your hot water habits, we aim to cover what others don’t (and with a uniquely Perth lens) when it comes to your next water heater overhaul. 

Impacts of water heater size

Choosing the right hot water system for your family isn’t just about having a comfortable shower in the morning. With water heating contributing to 27% of WA’s household energy use on average every year (only just behind heating and cooling for most people in Perth!), choosing the right size unit can have impacts on both your wallet and carbon footprint as well.

What do we mean?

According to a University of SA study funded by the Australian government, utilisation of the tank volume and system sizing is a major contributing factor to cost, greenhouse gas emissions and efficiency – meaning your wallet can be impacted by both undersizing and oversizing your next water heater if you’re not careful.

Undersizing can lead to inadequate hot water supplies, leaving you running out of hot water when you need it most. We’ve all felt the pain of trying to have a shower and being met with a cold water surprise!

Oversizing can lead to wasted money, both on the upfront installation and ongoing costs of running – leaving you out of pocket as you keep water heated that never leaves the tank.

But it’s not as easy as just looking at the tank size, as there’s more that goes into providing your hot water than meets the eye. After all, it’s not a disposable tank of water that’s used and replaced manually! From how quickly the unit can replace the hot water inside it to the amount of heat lost to getting from the unit to your taps, there’s a lot of thought that goes into making the right choice when it comes to upgrading your hot water system.

Coming prepared: Knowing your hot water demand 

While there’s a lot of experience that we take into account when sizing your next water heater, we still reckon it’s important to know what you’re spending your hard-earned money on. We also know there can be a lot of pressure when it comes to replacing your hot water system, and nobody wants to be ripped off or pressured into buying what they don’t need. The best way you can prepare yourself is to come prepared and have a proper, informed discussion with your friendly hot water professionals yourself. 

As we’ve mentioned, it’s not all about tank size though. With so many different builds, brands and overall options available on the market that all work in different ways, it’s important to consider not just your daily hot water usage, but what we call your peak hour demand. This measures the most demanding times you’ll be putting the system through, and is the best way to measure the size tailored to you. 

While many places will say to consider your current usage, we think it’s better to look at the size of your house rather than family size when choosing your next hot water system. After all, with the average hot water system lasting around 10-15 years here in Perth, nobody wants to be having cold showers once your teenager starts taking those long showers 9 years down the road! 

Note that this doesn’t mean you’ll necessarily need a system with a storage tank capacity that matches this demand. What’s more important here is how much hot water your system can supply per hour, including heating more cold water. Don’t be afraid to ask questions to one of our friendly hot water professionals to ensure you’re getting the best bang for your buck when you next upgrade your hot water system.

An easy, simple to use table to the rescue 

To help you and your family figure out your house’s unique hot water needs, we’ve put together an easy-to-use table below. Come prepared when choosing which hot water system you need with the right questions to ask your trusted professionals in the trade. 

Household sizeDaily hot water
usage – Average
Daily hot water
usage – High
2144 L217 L
3203 L326 L
4280 L434 L
5343 L543 L
6420 L651 L

How did we calculate these numbers?

Average water usage: 

  • Each person having 7-minute shower, using a shower head with an average flow rate of 9L/min (the maximum allowed flow rate for modern shower heads). 
  • Using a dishwasher consumes on average 14L per cycle (average modern washer usage). Cycles calculated at (number of people / 2) per day. 
  • Additional 2L per person per day for miscellaneous use including handwashing, shaving etc. 
  • No hot water consumed from washing machines.
  • Approximates ~70 L hot water consumed per person per day – in line with 76L average from SA study.

High water usage:

  • Each person having 7-minute shower, using a shower head with an average flow rate of 14L/min (the average flow rate for older shower heads in Australia).
  • Hand-washing dishes using on average 10.5L per person per day (average modern washer usage).
  • Additional 2L per person per day for miscellaneous use including handwashing, shaving etc. 
  • No hot water consumed from washing machines. 
  • Approximates ~109L hot water consumed per person per day – in line with the upper end of usage from the SA study.

Take these numbers and think about how we can apply this to your peak hot water demand. 

For instance, do you have a household of 4 (with one more on the way), and expect everyone to shower in the morning and run a load of dishes in the dishwasher shortly after – between 7 and 8am? You’ll need about 280 litres (4 x showers at a 9L/min flow rate x 7 minutes, + 14L dishwashing cycle) of hot water delivered in that hour every day. That’s not to mention an extra shower once the little one grows up! 

Which hot water system is best for my family?

Remember, every hot water system works differently. The actual size of water heater you’ll need will still depend on each individual product. The plus side is, by knowing how much hot water you and your family uses, you’ll be armed with the knowledge to choose a system tailored to your needs. 

If you’re looking at upgrading your hot water system, we’d recommend choosing something that both meets your needs and saves you money in the long run. When chatting to one of our friendly professionals here at Ritz Plumbing & Electrical, don’t be afraid to have a discussion on which system will achieve these goals. For instance, using the above information, we know that upgrading your old electric hot water system to a PV-offset heat pump system can save you up to a whopping 97% on your household hot water bills – from $27 to less than $1 to run that 280L of hot water.

When it comes to selecting the perfect hot water system size for your home, preparation is key. Understanding your household’s hot water usage patterns and peak demand times can lead to a more efficient and cost-effective choice. So, come prepared, use our handy calculator and speak to the friendly team at Ritz Plumbing & Electrical today. Chat to one of our friendly representatives now by calling 13 74 89 or send an enquiry using our easy online contact form.