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What size hot water system do I need?

Need a new hot water system? Confused about what hot water system you need? When it comes to choosing hot water systems it can be daunting as there aren't just one or two options on the market. There are storage or instantaneous, gas, electric, solar, heat pump ... the list goes on. And that's before you even get to sizing.

Hot Water

Choosing the best-sized hot water system for your needs can be a little daunting, which is why we have put together a little bit of information to help you out. From sizing guides to hot water types to questions to ask and everything in between, this page is a one-stop shop for all your hot water sizing needs.

If however, you have further questions, give Fallon Solutions a call on 1300 762 260 and one of our friendly team members would be more than happy to assist!

Sizing a hot water system

When looking at different hot water systems and their sizing, there are a few things to consider when making a decision on what option is best for your needs:

  • Storage hot water units: Sized according to how many people are in your house. Therefore, the more people that live in your home, the larger the storage hot water system you will require
  • Solar hot water systems: Just like storage hot water units, the sizing of solar systems is based on how many people are in your household.
  • Continuous flow/instantaneous hot water heaters: In comparison, continuous systems are sized according to how many hot water outlets you have in your home. The more outlets you have, the larger the system you will require.

Other points to consider are:

  • If you have a storage system that is too big, it will cost you large amounts of money as it will be heating and storing water you aren't using.
  • If you have a storage system that is too small, you will always run out of water!
  • If you have a continuous flow system that is too small, you will be unable to run multiple hot water outlets at once.
  • One person generally uses about 50L of hot water a day.
Household Water

Questions to ask when choosing a hot water unit

Some questions to ask when looking at the appropriate sizing of your hot water system include:

  • How many people live in your house?
  • Roughly how much water do you use?
  • When do you use your hot water?
  • Do you have a dishwasher?
  • Does everyone in your home shower in the morning or the evening?
  • Does your washing machine use hot or cold water?
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Hot water sizing tables

To make things a little easier, take a look at the following tables for hot water sizing for electric storage, gas and solar.

Electric Storage Hot Water Systems


Off-Peak Rate

Peak Rate

Number of persons serviced

Capacity (litres)

Number of persons serviced

Capacity (litres)


















Solar Hot Water Units


Number of persons serviced

Hot water delivery (litres per day)

Approx size of tank (litres)

Collector (m²)














Natural Gas and LPG Water Heaters



Continuous Flow

Number of persons serviced

Capacity (litres)

Number of outlets served at one time*

Flow rate (litres per minute)





















*Continuous flow systems are sized according to the required flow rate. A guide is often the number of bathrooms in the home. As always, consult the suppliers or manufacturers for specific sizing guidelines for their products.


Suggested systems for household types

In general, solar hot water systems are the best option for most (if not all) households of any size, as they are the cheapest to run and most efficient. If a solar heater is not an option, however, there are a few other suggestions for varying household sizes.

  • Household of 1-2 people: A gas or electric continuous flow system is the best option, or a small gas storage hot water unit.
  • Household of 3-4 people: A heat pump hot water system is a great choice, or a gas system (either storage or continuous flow).
  • Household of 5+: There are a few choice available - a large heat pump system is an option, as well as any continuous flow system that is available. A gas storage hot water system is also a great choice, as they are very economical.

Hot water for a family of four

Hot Water

To put it briefly, for a family of 4 you will need:

  • Electric Hot Water: A 125–160L tank for a continuous system or 250–315L for off-peak.
  • Gas Hot Water: A tank of about 135–170L, however there are also instantaneous system options.
  • Solar Hot Water: About four square metres of solar collector area (two panels) and a 300–360L tank.
  • Heat Pump Hot Water: A 270-315L tank.
Fallon Solutions

Your reliable and professional hot water experts

If you have any questions regarding the best hot water system size for your needs, or you would like to speak to one of the friendly team members regarding a hot water issue or project, give Fallon Solutions a call on 1300 762 260 and we would be happy to assist. We have years of industry experience when it comes to hot water, so get in contact now!



Australian Government - YourHome (Hot Water Service): http://www.yourhome.gov.au/energy/hot-water-service

Energy Rating (Water Heating): http://www.energyrating.gov.au/products/water-heaters

Sustainability Victoria (Choose a hot water system): https://www.sustainability.vic.gov.au/energy-efficiency-and-reducing-emissions/save-energy-in-the-home/water-heating/choose-the-right-hot-water-system

CHOICE (How to buy the best hot water system): https://www.choice.com.au/home-improvement/water/hot-water-systems/buying-guides/hot-water-systems


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