A hot shower or bath isn’t just a hygienic luxury, it’s great for calming the muscles and the mind, improving sleep, reducing inflammation and joint pain and improving circulation. And it’s not just about the bath or shower, either – because you also rely on your hot water system to wash the dishes, clothes, for cooking, cleaning and more. But do you keep running out of water, day after day? Knowing what size hot water system to buy in the first place is the best way to avoid that cold and frustrating problem.

What size hot water system do I need?

Updating your hot water system so you don’t keep getting stuck under a cold stream of water? There are even a few other reasons to ensure you make the right choice from all of those various hot water system sizes:

  • Don’t run out of water: If the tank, power or capacity size is too small, there won’t be enough pre-heated and stored hot water to get you from one main heating cycle to the next.
  • Be energy & cost-efficient: It’s not just about avoiding a hot water system that is too small – too big for your household’s needs, and you’ll just be wasting money on both the bigger ticket price and the ongoing energy costs.
  • Make your system last: If you ask an underpowered instantaneous hot water system to work too hard each day, it’ll dramatically speed up the wear and tear process. To keep those maintenance, repair and replacement bills low, a well-sized system is a must.

Convinced that choosing wisely from all those hot water system sizes is critical to keep those steaming showers flowing? Our Sydney plumbers have come up with a step-by-step guide on how to get a head-start on matching the right-sized hot water system to your property, family and needs:

1. What’s your overall demand?

Did you know each person in your home uses somewhere between 50-75 litres of hot water each and every day? For a family of four, that’s 200-300 litres per day – a helpful early guide to the sort of system capacity and tank size you’ll need. However, some people have big full baths, and very long showers – whilst others have short showers or even cold showers!

Also factor in the number of bathrooms in your home, as well as the non-bathing appliances that use hot water.

2. Try a hot water calculator

Most hot water system manufacturers or plumbers will be able to refer you to their own or third-party sizing charts and hot water usage calculators that are quite helpful for matching your home & lifestyle to the right system.

3. What flow/delivery rate do you need?

As well as tank capacity, two other critical considerations for hot water system sizes are the flow and the delivery rates. That’s basically the rate at which hot water is capable of being delivered from the system into your home and out of the taps at any given time. Get it wrong, and your shower could be a trickle rather than a satisfying flow, especially when another hot tap or outlet is turned on elsewhere in the home. As a rough guide:


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  • Electric hot water systems‘ flow rate is typically 20-25 litres per minute
  • Gas hot water systems‘ flow rate is typically a little higher – up to 40 litres a minute on average
  • Depending on the capacity, instant hot water systems have variable flow rates but the average is 10-32 litres per minute.
  • The water pressure in your area can affect the hot water flow rate.

We’ll help you choose hot water system sizes

However, it’s also important to consult with a hot water system plumber before deciding on the right hot water size, because you’ll also need to factor in the hot water system installation, the available energy sources, ongoing maintenance considerations and the best brands and warranties.

And here at Rapid Service Plumbing, we’ve installed, repaired and worked on so many different properties and hot water technologies that we can easily recommend the perfect hot water type, size, and model for your home & budget – no worries! For a no-obligation consultation & quote with a $0 call-out fee all across Sydney and beyond, get in touch with Rapid Service Plumbing’s hot water specialists today.