24/7 Plumbing Emergency Hotline Call 1300 721 996
Sales - AUSTRALIA WIDE Service & Installs - Sydney - Central Coast - Sunshine Coast - Brisbane - Newcastle - Wollongong - Melbourne - Perth - ACT

What size hot water system do I need? | Hot Water Installation

Whether you’re replacing an old hot water system or installing a completely new hot water unit, you can find yourself asking “what size hot water system do I need?”. Every household requires a different hot water system depending on a number of factors, such as the number of people in the home and the number of hot showers they typically take.

It’s important to understand why hot water system sizing is so significant, why your hot water habits impact your system, and the different hot water systems that are available. Keep reading to figure out how to choose the right size hot water system for you.

Why Is Hot Water System Size Important?

So, why is the size of your hot water system so important? It’s because the size determines the amount of hot water available for use. A system that is too small may result in running out of hot water, while a larger-than-necessary system can waste money and isn’t very energy efficient.

Finding the right hot water system for you and your household ensures optimal performance, efficiency, and instant hot water whenever you need it. This can save you a significant amount of time, money, and stress in both the short term and the long term.


Types of Hot Water Systems

The type of hot water system that you install can have a significant impact on a number of factors; your system’s lifespan, how instantaneous hot water will be delivered to your taps, shower heads, and other hot water outlets, whether you can easily access hot water during off peak times, and the hot water system sizes available.

There are 3 main types of hot water systems, 2 of which come in either storage tank systems or continuous flow systems. For reference, a storage tank system stores your hot water in a tank, whereas a continuous flow system delivers instantaneous hot water. The 3 types of systems are electric hot water systems, gas hot water systems, and solar hot water systems.

hot water system replacement

Electric Hot Water System

Continuous flow electric systems heat the water as it passes through a heat exchanger using an electric heating element. The water is heated on demand and there is no storage tank, which means that they’re suitable for households with low hot water usage.

They are generally more energy efficient than traditional storage hot water systems, as they only heat water when it is needed. However, it’s important to keep in mind that they require a larger electricity supply than other types of systems.

Electric storage hot water systems work by heating the water and storing it in a hot water tank for later use. The system contains heating elements that are powered by electricity to heat the water as it sits in the tank. Once the hot water is used, the tank refills and the heating element turns on to reheat once again.

These systems typically have a thermostat to regulate the water temperature and a pressure relief valve to prevent the tank from becoming over-pressurised. The storage tank can be installed either indoors or outdoors, varying in size depending on your household’s needs.

Heat pump hot water system VS. Electric hot water systems

While a heat pump hot water system uses electricity to operate, it’s important to understand that there are not the same as conventional electric hot water systems. Heat pump hot water systems are more energy efficient as they use a heat pump to transfer heat from the air or ground to heat the water.

This means that they use less electricity to heat the same amount of water compared to electric systems. However, they typically have a higher upfront cost.

Rheem 50L with Plug Electric

Gas Hot Water System

Continuous flow hot water gas systems work in a similar way to their electric hot water system counterparts, but use a gas burner to heat the water as it passes through the heat exchanger. The gas burner is controlled by a thermostat, which maintains the desired temperature of the water.

When a hot water tap is turned on, cold water enters the unit, which triggers the gas burner to heat the water. As hot water flows out of the unit, fresh cold water enters and the process repeats. This allows the system to supply hot water nearly endlessly.

Gas storage hot water systems work by using a gas burner to heat water stored in a tank. The burner heats the water to the desired temperature, and the heated water is drawn from the tank.

The hot water is then replaced by cold water, which is then heated by the burner, and the cycle continues. These systems usually have a pilot light to ignite the burner and a thermostat to regulate the water temperature.

Solar Hot Water System

Solar hot water systems use the sun’s energy to heat water as it flows through the solar collector area of panels. The heated water is then stored in a tank to be used later.

The system includes a gas or electric booster that kicks in when there isn’t enough solar energy to heat the water to your desired temperature. This ensures that hot water is available even during times with low sunlight or high demand.

Rheem stellar 360 litre gas hot water heater

Factors To Consider For Your Hot Water System

Choosing the right size hot water system is crucial for ensuring that your household has an adequate and efficient supply of hot water. There are several factors to consider when choosing the size of your hot water system.

These include the number of people in your household, how many showers and hot water taps you have in your home, the type of system you have, your average water usage, and the climate in your area.

Carefully consider how much hot water you need. A hot water system that’s too small can result in an inadequate supply of hot water, while a system that is too large can result in unnecessary energy costs. It’s important to consult with a professional plumber or hot water system installer to determine the appropriate size of your system.

Professionals can assess your household’s hot water usage and help you choose a system that’s suitable for your needs. Investing in the right size hot water system can supply you with the amount of water you need, all while saving you money on your energy bills.

Number Of People

The number of people in your household is an important factor in determining the size of the hot water system you need. Generally, the more people there are in your household, the larger the hot water system should be to meet everyone’s needs.

Typical Usage

If multiple people in your home like taking a hot shower, your hot water usage can add up quickly. Washing machines and other appliances that use hot water regularly are also important factors to consider.

When it comes to hot water system size, a larger unit is the best for households that have a higher-than-average usage of hot water. Likewise, a household that has a lower-than-usual usage of their hot water system can afford a smaller size.

Flow Rate

The flow rate of a hot water system refers to the volume of water that can be heated and delivered within a specific period. Flow rate is determined by the size of the hot water system and the available water pressure. In general, the higher the flow rate, the larger the hot water system required.

When selecting a hot water system, it’s crucial to choose a system with an appropriate flow rate to meet your household’s needs. If the flow rate is too low, you may experience a lack of hot water during peak usage times. On the other hand, if the flow rate is too high, you may end up purchasing a larger and more expensive hot water system than what you need.

Climate & Geographic Location

Climate and geographical location play a crucial role in determining the size of the hot water system you need. In colder areas, such as Tasmania and Victoria, a larger hot water system may be needed to ensure that there is enough hot water available to meet your household’s needs.

Conversely, in warmer areas, such as the Northern Territory and Queensland, a smaller hot water system may be suitable. Warmer temperatures require less energy to heat the water, which can result in a more efficient system. Additionally, in areas that experience more frequent and longer periods of sunlight, solar hot water systems may be a more suitable option as they can provide a sustainable and cost-effective solution for meeting hot water needs.

Energy Efficiency

The energy efficiency of a hot water heater can have a significant impact on the size of the hot water system you need. Consider the energy efficiency rating of your desired unit and choose a hot water system that is appropriate for your typical hot water usage.

Systems with a high energy efficiency rating can provide the same amount of hot water with a smaller tank or lower flow rate, helping to reduce your energy consumption and save on utility bills.


A larger unit will generally cost more to purchase and install, but may save money in the long run if it meets the needs of your household. However, it’s important to balance the upfront cost with ongoing expenses such as energy bills, maintenance, and potential repairs. It may be more cost-effective to choose a smaller unit as long as it still meets your household’s hot water needs.

In addition to the cost of the unit itself, the cost of installation should also be factored into your decision. Some types of hot water systems, such as solar or heat pump systems, may require more complex installation procedures and therefore cost more to install. However, these systems may provide long-term cost savings through energy efficiency

What System Do I Need? | How To Make A Decision

Choosing the right size hot water system is crucial to ensure that your household’s hot water needs are met. The number of people in your household, typical hot water usage, flow rate, climate, energy efficiency, and costs should all be taken into consideration when selecting the appropriate size hot water heater and system.

We recommended consulting with a licensed plumber or hot water system specialist before making a purchase to ensure that you’re choosing the most appropriate system for your specific needs. By taking the time to research and select the right hot water system, you can ensure that your household has access to a reliable and efficient supply of hot water for years to come.

bosch instantaneous gas hot water system

same day hot water service logo

Enter your username and password to log into your account