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Let’s face it: When it comes to hot water, all you want is to be able to turn on the tap when you want and get the steaming hot water you need and expect. In reality, however, it’s a little trickier than that – and why’s that? Because there are many great but vastly different technology types out there – and they all come in different sizes and capacities.

So after choosing between an electric or gas, instantaneous, solar or heat pump, tank or tankless, your next question is naturally, ‘What size hot water system do I need?’

It’s a question best answered by the local Melbourne plumbers, who spend each and every day matching hot water users with precisely the hot water system for their home, lifestyle, preferences, family size and budget. And, based on that expertise and experience, that’s exactly why we’re here to help with some simple advice.

First, it’s important to reiterate that the answer to what size hot water system you’ll need depends on the type of hot water system you’ve selected. Let’s break down the main ones:

Conventional Or ‘Tank’ Systems:

These systems are easily recognizable as they consist of a large cylindrical tank, inside of which water is heated using electricity, gas, solar power, or heat pump technology. After heating and storage, the hot water is readily available.

However, when the tank empties, you’ll need to wait for it to reheat, resulting in an unpleasant cold shower. The key to choosing the right system is matching the tank size with your family’s needs and daily hot water consumption. In essence, the more hot water your household requires, the larger the tank should be.

Instantaneous/Continuous Flow Systems:

If your hot water usage varies, with some days demanding an abundance of hot baths and showers, while others are less active, then opting for an instantaneous or tankless system could be a smart choice. In this scenario, the question shifts from "What size hot water system do I need?" to "What capacity hot water system do I require?". This is because, while an instant hot water system consistently delivers hot water from a single hot tap, trying to run multiple hot water outlets concurrently may challenge a smaller-capacity system.

What Size Hot Water System – Frequently Asked Questions

To narrow down your choice, even more, we’ve broken down all of the most common questions that people looking to size the ideal hot water system installation for their home or premises tend to ask:

1. How Much Water Do I Use Each Day?

If you’re the Average Joe or Jill, you probably use just shy of 50 litres every day. As you browse those tanks of capacity sizes, finding a match for your household should be quite straightforward – remembering to factor in whether your water usage is average, below average, or above average.

2. Is A Bath Per Day Still ‘Average Use’?

Actually, no. If you love a hot bath each and every day, that will cost you about 100 litres – making you an above-average hot water user. A typical shower, though, uses only about 18-20L.

3. Should I Buy A Huge System To Be On The Safe Side?

If you have deep pockets, that’s one way to go – but bear in mind that if your system is too big and powerful for your home’s needs, you’re simply paying unnecessary money up-front for a big unit, and then for the rest of time heating a lot of water that you’ll rarely use.

4. Ok, What Size Hot Water System Do I Need, Then?

As we’ve tried to demonstrate, there’s no simple answer to that question because it depends on how you answer questions like these:

  • How many people use hot water in your house?
  • How much water does each person use?
  • What time of day is your ‘peak’ hot water usage?
  • Does your dishwasher or washing machine use hot water?

To give you a rough guide, we’d probably recommend small tank storage or continuous flow system for a couple, an efficient heat pump system for 3-4 people, or a large tank for heavy use or more prominent families.

To quickly put it in numbers:

  • 1-4 people: 90-130L tank
  • 2-5 people: 130-170L tank
  • 4-6 people: 200L tank
  • 5-9 people: 260L tank


  • One outlet per usage: 16 litres-per-minute flow
  • 2-3 outlets per usage: 20L-24L/pm flow
  • 3+ outlets per usage: 32L/pm flow

For The Exact Answer For You, Call An Expert

So while there isn’t a definitive answer to ‘What size hot water system do I need’, hopefully, this guide has at least pointed you in the right direction. To get the perfect match for your home, lifestyle and budget, you’ll have to talk to the professionals directly – and here at Ezy-Plumb, we’re always happy to oblige! Need a plumber in Bentleigh, Elwood, Mentone or Murrumbeena? Get in touch today! We work across the Melbourne bayside area and into the south-eastern suburbs. With our gas and electrical licenses, we can supply and install new hot water systems from start to finish with guaranteed workmanship.

Petros Ttofari
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