What Size Hot Water System Do I Need? Complete Guide for Australian Homes

Choosing the right size hot water system depends on your household size, number of bathrooms, daily hot water use, energy source and the type of system you are buying. A small home may only need a compact storage tank or lower-flow instant system, while a larger family home may need a bigger tank, faster recovery or a higher-flow continuous hot water unit.

At Hot Water Outlet, you can compare hot water systems online by type, brand, capacity, flow rate and household suitability, including electric hot water systems, heat pump hot water systems, gas hot water systems and instant gas hot water systems.

Quick Answer: What Size Hot Water System Do I Need?

As a general guide, smaller households usually need less hot water storage or a lower flow rate, while larger households need more capacity or stronger continuous flow performance.

The right size depends on:

• Number of people in the home

• Number of bathrooms

• Shower habits

• Bath use

• Kitchen and laundry hot water use

• Whether hot water is used at the same time in different areas

• System type

• Energy source

• Tank recovery rate

• Flow rate for instant systems

• Current hot water setup

For storage systems, size is usually measured by tank capacity in litres. For instant gas hot water systems, sizing is usually based on flow rate in L/min.

If you are unsure where to start, compare the full hot water systems range first, then narrow your choice by system type, household size and product specifications.

Hot Water System Size Guide by Household

This table is only a general guide. The right choice still depends on your home, usage patterns, energy source, existing system and product specifications.

Storage Systems vs Instant Systems: Why Sizing Works Differently

Hot water system sizing depends heavily on the type of unit.

A storage hot water system keeps heated water in a tank. This includes most electric hot water systems, heat pump hot water systems and many gas hot water systems. These are usually compared by tank capacity in litres.

An instant hot water system heats water as it flows through the unit. This includes most instant gas hot water systems and some instant electric hot water systems. Instant gas systems are usually compared by flow rate in L/min.

That means a 250L storage tank and a 26 L/min instant gas unit cannot be compared directly. One stores hot water. The other produces hot water on demand.

How to Size an Electric Hot Water System

Electric storage hot water systems are usually chosen by tank capacity. The right size depends on how much hot water the household uses and how quickly the system can recover.

An electric hot water system may be suitable when the property already has electric storage and the goal is a straightforward replacement.

When choosing an electric hot water size, consider:

• Number of people in the home

• Number of showers per day

• Whether people shower back-to-back

• Bath use

• Laundry use

• Kitchen hot water demand

• Current tank size

• Whether the old system often runs out

• Available space

• Power requirements

• Recovery rate

• Connection positions

If your current electric tank has always supplied enough hot water, a similar size may be a practical starting point. If the household now runs out of hot water often, it may be worth comparing a larger tank or a different system type.

Common Electric Hot Water Sizes

Electric hot water systems come in a range of sizes. Smaller units may suit compact homes, point-of-use applications or lower-demand properties. Larger tanks may suit family homes with higher hot water use.

Common electric storage sizes include:

• Small units for compact or point-of-use use

• Medium tanks for smaller households

• Larger tanks for family homes

• High-capacity tanks for heavier hot water demand

The best electric hot water size is not always the largest one available. The goal is to match tank capacity to actual household demand while also checking space, recovery rate and connection requirements.

How to Size a Heat Pump Hot Water System

A heat pump hot water system is also a storage system, so tank capacity matters. Heat pumps are often chosen by households wanting an efficient electric hot water option.

Heat pump sizing is commonly based on:

• Number of people in the home

• Daily hot water use

• Tank capacity

• Recovery performance

• Outdoor location

• Airflow

• Noise rating

• Available space

• Household routines

• Current electric storage size

A heat pump may be worth comparing if you are replacing an older electric storage system and want to consider a more efficient electric option. However, the system still needs to suit the location. Heat pumps need appropriate space and airflow, so sizing is not only about litres.

Common Heat Pump Hot Water Sizes

Many homes compare medium to larger heat pump tanks because heat pumps are often selected for regular household hot water demand.

Common heat pump considerations include:

• Smaller household demand

• Family household demand

• Larger tank capacity for heavier use

• Outdoor installation space

• Air movement around the unit

• Product dimensions

• Noise rating

• Warranty information

If a home has higher hot water demand, a larger heat pump may be worth comparing. If the location is tight or airflow is limited, the product specifications need to be checked carefully before ordering.

How to Size a Gas Storage Hot Water System

Gas storage hot water systems are sized by tank capacity and recovery rate. They store hot water in a tank, but the water is heated using natural gas or LPG.

A gas hot water system may suit homes that already use gas storage and want a traditional replacement option.

When sizing gas storage, check:

• Tank capacity

• Recovery rate

• Household size

• Number of bathrooms

• Natural gas or LPG

• Current gas storage size

• Existing location

• Dimensions

• Connection positions

• Pressure rating

• Product specifications

Gas storage sizing can be different from electric storage sizing because recovery rate can vary by model. Do not rely on tank capacity alone. Always compare the product details.

How to Size an Instant Gas Hot Water System

Instant gas systems are sized by flow rate in L/min. Instead of storing hot water, they heat water as it passes through the unit.

An instant gas hot water system may suit homes with natural gas or LPG where continuous flow hot water is preferred over a storage tank.

When sizing instant gas hot water, consider:

• Flow rate in L/min

• Number of bathrooms

• Number of hot water outlets

• Whether multiple outlets run at once

• Shower flow demand

• Natural gas or LPG

• Controller options

• Outdoor location

• Current gas setup

• Household size

• Product specifications

Common flow rate choices include smaller continuous flow units for lower-demand homes and larger units for homes with higher hot water use.

16L vs 20L vs 26L Instant Gas Hot Water

Instant gas systems are commonly compared by flow rate. A 16 L/min system, 20 L/min system and 26 L/min system are not designed for the same level of demand.

The right flow rate depends on the home. A larger number does not automatically mean the best choice, but an undersized instant gas unit may struggle if multiple hot water outlets are used at the same time.

How to Size an Instant Electric Hot Water System

Instant electric hot water systems are usually suited to compact point-of-use applications, not every whole-home hot water requirement.

Instant electric sizing depends on:

• Intended use

• Flow demand

• Electrical requirements

• Fixture type

• Location

• Product specifications

• Available power supply

These systems should be selected carefully. Always check whether the product is suitable for the intended application and confirm electrical requirements before ordering.

What Size Hot Water System for 1 Person?

A one-person household usually has lower hot water demand, but the right size still depends on shower length, bath use, laundry use and kitchen use.

Possible options may include:

• Smaller electric storage systems

• Compact storage tanks

• Suitable instant gas systems if gas is available

• Instant electric for specific point-of-use applications

• Smaller heat pump options where suitable

If the home already has a system that works well, the existing tank size or flow rate is a useful starting point. If the current system is much larger than needed, a smaller replacement may be worth comparing.

What Size Hot Water System for 2 People?

A two-person household may suit a small to medium storage system or a suitable instant gas unit, depending on the home.

Compare:

• Electric hot water systems for simple storage replacements

• Heat pump hot water systems for efficient electric storage options

• Instant gas hot water systems where natural gas or LPG is available

• Gas hot water systems for gas storage replacements

For two people, the biggest factors are shower habits, whether hot water is used at the same time and whether the current system runs out.

What Size Hot Water System for 3 People?

A three-person household usually needs to move beyond very small hot water options unless hot water use is light.

Consider:

• Medium electric storage

• Medium heat pump storage

• Gas storage with suitable recovery

• Instant gas with a flow rate matched to demand

If there are multiple bathrooms or back-to-back showers, do not choose based on household size alone. Usage pattern matters.

What Size Hot Water System for 4 People?

A four-person household usually needs a system that can handle regular daily demand. This often means a medium to larger storage tank, a suitable heat pump or an instant gas unit with enough flow rate.

For a family of four, compare:

• Tank capacity

• Recovery rate

• Number of bathrooms

• Morning and evening shower demand

• Bath use

• Laundry and kitchen use

• Energy source

• Whether outlets are used at the same time

A family of four with one bathroom may have very different requirements from a family of four with two bathrooms and frequent simultaneous hot water use.

What Size Hot Water System for 5 or More People?

Larger households need careful sizing. Running out of hot water is more likely when multiple people shower close together, especially if the tank is too small or recovery is slow.

For five or more people, compare:

• Larger electric storage systems

• Larger heat pump hot water systems

• Gas storage systems with suitable recovery

• Higher-flow instant gas hot water systems

• Existing energy source

• Number of bathrooms

• Peak usage periods

• Product specifications

For large households, the right system is not just about capacity. Recovery rate, flow rate, timing of use and system type all matter.

What Size Hot Water System for a Small Home or Unit?

Small homes, units and townhouses may have less space for a hot water system, but that does not automatically mean the smallest unit is the right choice.

For small homes, check:

• Number of occupants

• Available cupboard, wall or outdoor space

• Current system location

• Access for delivery

• Electrical or gas supply

• Tank capacity or flow rate

• Connection positions

• Body corporate or building requirements where relevant

A compact electric hot water system, suitable instant gas hot water system or instant electric hot water system may be worth comparing depending on the property.

What Size Hot Water System for a Family Home?

Family homes usually need stronger hot water performance than small units. The right size depends on the number of people, bathrooms, showers, baths and hot water routines.

For family homes, compare:

• Medium to large electric storage

• Medium to large heat pump storage

• Gas storage with good recovery

• Instant gas systems with suitable flow rate

• Correct natural gas or LPG model

• Required valves, fittings and pipework

Families should avoid choosing only by price. A system that is too small may create daily frustration, while a system that is poorly matched to the property may create replacement complications.

What Size Hot Water System for a Rental Property?

Rental properties need practical, reliable hot water sizing. The best option is usually one that suits the number of occupants, existing system type and property layout.

For rentals, consider:

• Current system type

• Existing tank size or flow rate

• Number of bedrooms

• Number of bathrooms

• Likely tenant demand

• Ease of like-for-like replacement

• Brand and warranty information

• Required valves and fittings

• Delivery access

A like-for-like replacement can often be the simplest starting point, but it is still worth comparing the full hot water systems range before ordering.

What Size Hot Water System for a Renovation?

Renovations can change hot water demand. A bathroom renovation, kitchen renovation, laundry upgrade or second bathroom can all increase the amount of hot water needed.

Before choosing a size for a renovation, think about the finished home, not just the current home.

Ask:

• Will there be more bathrooms?

• Will there be a larger bath?

• Will more people use hot water at once?

• Is the kitchen being moved?

• Is the laundry being upgraded?

• Will the current system location change?

• Will new valves, fittings or pipework be needed?

Browse valves, pipework and fittings if your project also needs hot water accessories or connection parts.

Should I Choose the Same Size as My Old Hot Water System?

The old system size is a useful starting point, but it should not be the only factor.

Choosing the same size may make sense if:

• The old system worked well

• The household size has not changed

• The number of bathrooms has not changed

• Hot water rarely ran out

• The current location still suits

• You want a like-for-like replacement

You may need to compare a different size if:

• The old system often ran out

• More people now live in the home

• A new bathroom has been added

• The household uses more hot water

• You are changing from storage to instant

• You are changing from electric to heat pump

• You are changing from gas storage to instant gas

Can a Hot Water System Be Too Big?

Yes, a hot water system can be larger than needed. A larger tank may cost more to buy, take up more space and may not be necessary for a smaller household.

However, undersizing can also be a problem. A system that is too small may run out of hot water, recover too slowly or fail to keep up during peak use.

The goal is balance. Choose a system that suits daily use without oversizing unnecessarily.

Can a Hot Water System Be Too Small?

Yes. A hot water system that is too small may run out during showers, struggle with multiple users or fail to meet morning and evening demand.

Signs your current system may be undersized include:

• Hot water runs out quickly

• Back-to-back showers are difficult

• The system struggles when the washing machine or kitchen is used

• Larger households need to stagger showers

• The system no longer suits the home after renovations

If this sounds familiar, compare a larger storage tank, a system with better recovery or an instant gas unit with a more suitable flow rate.

Sizing Checklist Before You Order

Before ordering a hot water system online, check:

• How many people live in the home

• Number of bathrooms

• Number of showers per day

• Bath use

• Kitchen hot water demand

• Laundry hot water demand

• Whether outlets are used at the same time

• Current system type

• Current tank size or flow rate

• Current energy source

• Natural gas or LPG if gas

• Tank recovery rate

• Flow rate in L/min for instant gas

• Product dimensions

• Connection positions

• Pressure rating

• Indoor or outdoor suitability

• Heat pump airflow requirements if relevant

• Power requirements

• Required valves and fittings

• Delivery access

• Warranty information

Common Sizing Mistakes to Avoid

Choosing by Household Size Only

Household size matters, but it is not the only factor. A two-person home with long showers and a large bath may use more hot water than a three-person home with short showers.

Comparing Litres and L/min as the Same Thing

Storage systems are measured by tank capacity in litres. Instant gas systems are measured by flow rate in L/min. These are different sizing methods.

Replacing With the Same Size Without Thinking

The old size may be right, but it may also be outdated. If the household has changed, the system size may need to change too.

Ignoring Recovery Rate

For storage systems, tank capacity is only part of the picture. Recovery rate can affect how quickly the system can heat more water after use.

Forgetting Gas Type

If choosing gas hot water, make sure you select the correct natural gas or LPG model. They are not interchangeable.

Not Checking Dimensions

A system may have the right capacity but still be unsuitable if it does not physically fit the available space.

Forgetting Valves and Fittings

Some replacements may require valves, fittings or pipework. Check the full hot water order, not just the main unit.

Best Hot Water System Categories to Compare by Size

Electric Storage Hot Water

Choose electric hot water systems if you are looking for a storage tank option, especially for like-for-like electric replacements.

Heat Pump Hot Water

Choose heat pump hot water systems if you want to compare efficient electric storage options and your home has a suitable location.

Gas Storage Hot Water

Choose gas hot water systems if your property already uses gas storage and you want to compare natural gas or LPG replacement options.

Instant Gas Hot Water

Choose instant gas hot water systems if you want continuous flow gas hot water and need to compare flow rates in L/min.

Instant Electric Hot Water

Choose instant electric hot water systems for suitable compact point-of-use hot water applications.

Trusted Brands to Compare

Hot Water Outlet brings together recognised hot water brands so customers can compare system sizes, product types and specifications in one place.

Depending on the system type and size you need, you may want to compare:

• Rheem hot water systems

• Rinnai hot water systems

• Dux hot water systems

• Bosch hot water systems

• iStore hot water systems

• Envirosun hot water systems

• Stiebel Eltron hot water systems

• Vulcan hot water systems

• Emerald Energy hot water systems

Brand can help narrow your search, but sizing should always be based on system type, household demand, energy source, capacity, flow rate and product specifications.

FAQs About Hot Water System Sizing

What size hot water system do I need for a family of 4?

A family of four usually needs a medium to larger storage tank or an instant gas system with a suitable flow rate. The right size depends on the number of bathrooms, shower habits, bath use, kitchen use, laundry use and whether hot water is used at the same time in different areas.

What size hot water system do I need for 2 people?

A two-person household may suit a small to medium storage system or a suitable instant gas unit, depending on usage. If both people shower back-to-back or use a lot of hot water, a larger option may be worth comparing.

Is a bigger hot water system better?

Not always. A bigger system may be useful for higher-demand households, but oversizing can cost more and take up more space than needed. The best size is the one that matches actual hot water use.

What size instant gas hot water system do I need?

Instant gas hot water systems are sized by flow rate in L/min. The right flow rate depends on the number of bathrooms, hot water outlets, shower demand and whether multiple outlets are used at the same time.

What size electric hot water system do I need?

Electric storage hot water systems are sized by tank capacity in litres. The right size depends on household size, shower use, bath use, laundry use, recovery rate and whether the current system runs out of hot water.

What size heat pump hot water system do I need?

Heat pump hot water systems are sized by tank capacity, but location and airflow also matter. Choose a size that suits household demand and check the product dimensions, outdoor space, noise rating and airflow requirements.

Should I replace my hot water system with the same size?

Replacing with the same size may be suitable if the old system worked well and household demand has not changed. If the old system often ran out, the household has grown or you have added bathrooms, compare different sizes before ordering.

What happens if my hot water system is too small?

A system that is too small may run out of hot water, recover too slowly or struggle during peak use. For instant gas, a flow rate that is too low may not suit multiple outlets or higher household demand.

What happens if my hot water system is too large?

A system that is larger than needed may cost more to buy and may take up more space. The goal is to choose a system that matches the home without oversizing unnecessarily.

Do I need a licensed tradesperson to confirm hot water sizing?

If you are unsure about sizing, gas type, electrical requirements, connection positions or suitability, speak with a licensed plumber, gas fitter or electrician before ordering. Hot Water Outlet helps customers compare and order supply-only hot water systems and accessories online, while installation and connection work should be handled by licensed professionals.

Compare Hot Water System Sizes Online

The right hot water system size depends on your household, energy source, system type and daily hot water demand. Storage systems are compared by litres. Instant gas systems are compared by flow rate in L/min. Heat pumps need both the right tank size and a suitable location.

Browse hot water systems online with Hot Water Outlet to compare electric, gas, instant gas, instant electric and heat pump options by size, brand and product specifications.