What Size Gas Hot Water System Do I Need?

Jun 8, 2026

Choosing the right size gas hot water system depends on whether you are buying gas storage or instant gas hot water. Gas storage systems are sized by tank capacity and recovery rate, while instant gas hot water systems are sized by flow rate in L/min. The right choice also depends on household size, bathrooms, shower habits, natural gas or LPG supply, available space and whether your current system has been keeping up.

At Hot Water Outlet, you can compare gas hot water systems online, along with instant gas hot water systems, hot water systems, electric hot water systems, heat pump hot water systems and common valves, pipework and fittings.

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

The right size gas hot water system depends on the system type.

As a general guide:

Choose gas storage by tank capacity, recovery rate, household size and daily hot water demand.
Choose instant gas hot water by flow rate in L/min, number of bathrooms and whether multiple hot water outlets may run at once.
Choose a smaller gas storage or lower-flow instant gas system for smaller homes with lower demand.
Choose a medium gas storage or 20 L/min instant gas system for moderate household use.
Choose a larger gas storage or 26 L/min instant gas system for family homes, two-bathroom properties and higher peak demand.
Always confirm natural gas or LPG before ordering, because gas systems are not interchangeable.
Check gas supply, water pressure, dimensions, connection positions and required valves before buying.

If you are replacing an existing gas system, start by checking the current model, tank size or flow rate. If it has been keeping up well, a similar size may be practical. If it struggles during showers or runs out often, compare a larger capacity, stronger recovery rate or higher-flow instant gas system before ordering.

Gas Hot Water Sizing at a Glance

Household Type	Gas Storage Size Direction	Instant Gas Size Direction	Main Thing to Check
1 person	Smaller gas storage may suit	16 L/min may suit some homes	Shower habits and gas type
2 people	Small to medium gas storage may suit	16 L/min or 20 L/min may suit	Back-to-back showers
3 people	Medium gas storage often worth comparing	20 L/min often worth comparing	Bathroom count and peak use
Family of 4	Medium to larger gas storage may suit	20 L/min or 26 L/min may suit	Showers, bath use and outlet overlap
Family of 5+	Larger gas storage or stronger recovery may be needed	26 L/min often worth comparing	Multiple bathrooms and peak demand
One bathroom	Smaller to medium gas system may suit	16 L/min or 20 L/min may suit	Shower and kitchen overlap
Two bathrooms	Larger storage or stronger recovery may suit	20 L/min or 26 L/min often worth comparing	Whether two showers may run close together
Rental property	Size for likely tenant demand	Size for bedrooms and bathrooms	Avoid undersizing
Renovation	Size for the finished layout	Size for future bathrooms and fixtures	Do not size from the old layout only

This is a general guide only. The right size still depends on natural gas or LPG type, gas supply, water pressure, current system performance and product specifications.

Gas Storage vs Instant Gas: Why Sizing Is Different

Gas hot water systems are usually split into two main categories: gas storage and instant gas.

A gas storage system heats and stores hot water in a tank. It is sized by tank capacity and recovery rate.

An instant gas hot water system heats water as it flows through the unit. It does not store a large tank of hot water. It is sized by flow rate in L/min.

This means gas storage and instant gas cannot be compared using the same measurement.

System Type	How It Is Sized	Best Compared By
Gas storage hot water	Tank capacity and recovery rate	Litres, recovery, gas type and household demand
Instant gas hot water	Flow rate	L/min, gas type, bathrooms and simultaneous use

If you want a traditional tank-style system, compare gas hot water systems. If you want continuous flow gas hot water, compare instant gas hot water systems.

What Affects Gas Hot Water System Size?

Gas hot water sizing depends on how the home uses hot water during peak times.

Important sizing factors include:

Number of people in the home
Number of bathrooms
Number of showers per day
Whether showers happen back-to-back
Whether two showers may run at once
Bath use
Kitchen hot water use
Laundry hot water use
Current system tank size or flow rate
Whether the current system keeps up
Natural gas or LPG type
Gas supply suitability
Water pressure and flow
Available space
Product dimensions
Required valves and fittings

A home with three people and two bathrooms may need a stronger gas hot water system than a home with four people and one bathroom if peak demand is higher.

Natural Gas vs LPG: Check This First

Before choosing a gas hot water system size, confirm whether the property uses natural gas or LPG.

Natural gas and LPG hot water systems are not interchangeable. A system designed for natural gas should not be ordered for an LPG property, and an LPG model should not be ordered for a natural gas property.

Check:

Current hot water unit label
Gas meter
LPG bottle setup
Existing appliance details
Product listing gas type
Licensed gas fitter advice if unsure

Choosing the wrong gas type can cause delays, compatibility issues and extra costs. Always confirm natural gas or LPG before ordering a gas hot water system online.

What Size Gas Hot Water System for 1 Person?

A one-person household usually has lower hot water demand, but shower habits still matter.

For one person, consider:

Shower length
Number of showers per day
Bath use
Kitchen use
Laundry use
Whether guests often stay
Current system performance
Natural gas or LPG type

A smaller gas storage system or lower-flow instant gas system may suit some one-person homes. If the home has a bath, long showers or regular guest use, compare capacity and flow rate more carefully.

What Size Gas Hot Water System for 2 People?

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

For two people, consider:

Back-to-back showers
Whether both people shower around the same time
Kitchen hot water use
Laundry use
Bath use
Number of bathrooms
Existing gas system size
Current performance

A 16 L/min instant gas system may suit some lower-demand homes, while a 20 L/min model may be worth comparing where demand is higher or outlets sometimes overlap.

What Size Gas Hot Water System for 3 People?

A three-person household often needs moderate gas hot water performance, especially where showers happen close together.

For three people, compare:

Medium gas storage options
Gas storage recovery rate
20 L/min instant gas systems where suitable
16 L/min instant gas only for lower-demand homes
Current system performance
Number of bathrooms
Bath use
Peak morning and evening demand

A three-person home with two bathrooms may need more flow rate or stronger recovery than a one-bathroom home with the same number of people.

What Size Gas Hot Water System for a Family of 4?

A family of 4 usually needs stronger gas hot water performance because daily demand is higher.

For a family of 4, consider:

Number of bathrooms
Back-to-back showers
Whether two showers may run close together
Bath use
Kitchen use
Laundry use
Morning and evening peak demand
Current gas storage tank size or instant gas flow rate
Whether the current system struggles

A medium to larger gas storage system may suit some family homes. For instant gas, 20 L/min or 26 L/min models are commonly compared depending on demand, bathroom count and gas supply suitability.

What Size Gas Hot Water System for a Family of 5 or More?

A family of 5 or more usually needs larger capacity, stronger recovery or higher instant gas flow rate.

For larger families, consider:

Number of people in the home
Number of bathrooms
Teenagers or long showers
Two showers running close together
Bath use
Heavy laundry demand
Kitchen use during shower periods
Peak morning and evening use
Current system performance

A larger gas storage system or 26 L/min instant gas system may be worth comparing for larger households. The correct choice depends on natural gas or LPG type, gas supply, water pressure and product specifications.

What Size Gas Hot Water for One Bathroom?

A one-bathroom home may not need the same capacity or flow rate as a two-bathroom home, but usage still matters.

For one-bathroom homes, check:

Number of occupants
Shower length
Back-to-back shower use
Bath use
Kitchen and laundry overlap
Current system performance

A smaller to medium gas storage system may suit some one-bathroom homes. For instant gas, 16 L/min or 20 L/min may be worth comparing depending on household demand.

What Size Gas Hot Water for Two Bathrooms?

A two-bathroom home needs more careful gas hot water sizing because there is a higher chance of simultaneous hot water use.

For two-bathroom homes, check:

Whether two showers may run at once
Whether showers happen back-to-back
Number of people in the home
Bath use
Kitchen and laundry overlap
Current system performance
Gas supply suitability

For instant gas, 20 L/min or 26 L/min models are often worth comparing. For gas storage, tank capacity and recovery rate both matter.

What Size Gas Hot Water for Homes With a Bath?

Bath use can increase hot water demand significantly.

For homes with a bath, consider:

Bath size
How often the bath is used
Whether showers are used soon after filling the bath
Number of children or occupants
Current system performance
Gas storage recovery rate
Instant gas flow rate

A small gas storage system may struggle if a bath is used regularly. A lower-flow instant gas unit may also be unsuitable if the bath, shower and other outlets overlap.

Gas Storage Sizing: Tank Capacity and Recovery Rate

Gas storage systems are sized by tank capacity and recovery rate.

Tank capacity tells you how much hot water the tank stores. Recovery rate helps indicate how quickly the system can heat more water after hot water has been used.

Recovery rate matters for:

Families
Back-to-back showers
Bath use
Rental properties
Two-bathroom homes
Homes with heavy morning or evening demand

Two gas storage systems with similar tank sizes may perform differently if recovery rates differ. Always check product specifications before ordering.

Instant Gas Sizing: Flow Rate in L/min

Instant gas hot water systems are sized by flow rate in L/min.

Common instant gas sizes include:

16 L/min
20 L/min
26 L/min

A 16 L/min system may suit smaller homes with lower demand. A 20 L/min system may suit moderate demand. A 26 L/min system is commonly compared for larger homes, families and two-bathroom properties.

The right instant gas size depends on how much hot water the household needs at peak times, not just how many people live there.

16L vs 20L vs 26L Gas Hot Water

Flow Rate	Common Use Case	Main Thing to Check
16 L/min	Smaller homes, units or lower-demand one-bathroom properties	Gas type, shower demand and outlet overlap
20 L/min	Moderate household demand or small family homes	Bathrooms, shower timing and peak use
26 L/min	Larger homes, families or higher-demand two-bathroom properties	Gas supply, water pressure and product suitability

A 16 L/min system is not automatically enough for every small home. A 26 L/min system is not automatically required for every family. The best flow rate depends on peak demand and property suitability.

Gas Supply Matters When Choosing Size

A higher-capacity gas hot water system still needs suitable gas supply.

Gas supply suitability can be affected by:

Natural gas or LPG setup
Existing gas line sizing
Distance from gas meter or LPG bottles
Other gas appliances
Regulator setup
System location
Product requirements

This is especially important when choosing a 26 L/min instant gas system or changing from gas storage to instant gas. A licensed gas fitter should confirm suitability before connection work.

Water Pressure and Flow Matter Too

Gas hot water performance can also depend on the property’s water pressure and flow.

Before choosing a larger gas system, consider:

Existing water pressure
Shower flow rates
Number of outlets
Whether multiple fixtures run together
Pipework condition
Product specifications

If the home has low water pressure or flow issues, choosing a larger hot water system may not solve the underlying problem. A licensed tradesperson should assess the setup where needed.

What Size Gas Hot Water for Units?

Some units may use gas hot water where the building setup allows it.

For units, check:

Existing system type
Natural gas or LPG availability
Number of occupants
Number of bathrooms
External wall location if instant gas
Body corporate or building rules
Product dimensions
Gas type
Delivery access
Required valves and fittings

A lower-flow instant gas system or smaller gas storage unit may suit some units, but building suitability matters.

What Size Gas Hot Water for Townhouses?

Townhouses may suit gas hot water where natural gas or LPG is available and the system location is suitable.

For townhouses, check:

Number of occupants
Number of bathrooms
Whether showers overlap
Garage, courtyard or wall location
Natural gas or LPG
Gas supply suitability
Body corporate or complex rules if relevant
Product dimensions
Connection positions

A 20 L/min or 26 L/min instant gas system may be worth comparing for many townhouses, especially where there are multiple occupants or two bathrooms.

What Size Gas Hot Water for Rental Properties?

Rental properties should be sized for likely tenant demand, not only the current tenant.

For rentals, check:

Number of bedrooms
Number of bathrooms
Likely number of occupants
Current system size
Whether tenants have reported hot water issues
Gas type
Warranty information
Product availability
Required valves and fittings

Avoid choosing the smallest gas hot water system for a rental just to reduce upfront cost. If it is undersized, it can create tenant complaints and poor performance.

What Size Gas Hot Water for Renovations?

Renovations should be sized for the finished home, not the old layout.

For renovations, consider:

Future number of bathrooms
Larger bath or shower
Kitchen changes
Laundry changes
Whether two outlets may run together
Whether the system is moving
Natural gas or LPG type
Gas supply suitability
Required valves and fittings

If the renovation adds a second bathroom, larger bath or extra occupants, the old gas system size may no longer suit the home.

Replacing an Existing Gas Storage System

If you are replacing gas storage, start by checking the current unit.

Look for:

Brand
Model number
Tank capacity
Natural gas or LPG
Recovery information where available
Pressure rating
Manufacturing date
Existing location
Product dimensions
Connection positions

If the old gas storage system supplied enough hot water, a similar size may be practical. If it often ran out, compare larger capacity or stronger recovery before ordering.

Replacing an Existing Instant Gas System

If you are replacing instant gas, start by checking the current unit’s flow rate.

Look for:

Brand
Model number
Flow rate in L/min
Natural gas or LPG
Controller setup
Existing location
Product dimensions
Connection positions
Manufacturing date

If the current instant gas system keeps up well, a similar flow rate may suit. If it struggles when multiple outlets are used, compare a higher-flow model where the gas and water supply can support it.

Changing From Gas Storage to Instant Gas

Some homes compare instant gas when replacing old gas storage. This can be practical, but storage and instant gas systems have different sizing and connection requirements.

Before changing from gas storage to instant gas, check:

Natural gas or LPG type
Gas supply suitability
Required flow rate in L/min
Number of bathrooms
Household peak demand
Outdoor wall location
Product dimensions
Connection positions
Required valves and fittings
Controller preferences

Changing from storage to instant gas should be assessed by licensed tradespeople.

Changing From Instant Gas to Gas Storage

Some homes may prefer gas storage because they want a tank-style system or are replacing an existing gas storage setup.

Before changing from instant gas to gas storage, check:

Natural gas or LPG
Available space for a tank
Tank capacity
Recovery rate
Existing pipework
Product dimensions
Connection positions
Household demand
Required valves and fittings

The system should be selected by demand and property suitability, not just system type.

Gas Hot Water vs Electric Hot Water Sizing

Gas and electric systems are sized differently depending on the type.

Gas storage and electric storage are both tank systems, but recovery rates and energy source differ. Instant gas is sized by L/min. Electric storage is sized by litres.

Comparison Point	Gas Hot Water	Electric Hot Water
Energy source	Natural gas or LPG	Electricity
Storage sizing	Tank capacity and recovery	Tank capacity and recovery
Instant sizing	Flow rate in L/min	Usually point-of-use and electrical requirements
Key check	Gas type and gas supply	Power requirements
Best for	Homes already using gas	Homes without gas or already using electric storage

If your home does not have natural gas or LPG, compare electric hot water systems or heat pump hot water systems.

Should You Choose a Bigger Gas Hot Water System?

A bigger gas hot water system may be worth comparing if the current system struggles or household demand has increased.

A bigger system may suit when:

More people now live in the home
A second bathroom has been added
Showers happen back-to-back
Two showers may run close together
Bath use has increased
Laundry demand is higher
Tenants have complained about hot water
Renovations will increase demand

However, bigger is not automatically better. The system still needs to suit gas supply, water pressure, available space and product requirements.

Should You Choose a Smaller Gas Hot Water System?

A smaller gas hot water system may suit if demand has reduced or the old system was oversized.

A smaller system may suit when:

Fewer people now live in the home
The home has one bathroom
Hot water use is light
The old system was sized for a larger household
A compact replacement is needed
The current system is larger than necessary

Do not choose smaller by price alone. The system still needs to meet peak demand.

Common Mistakes When Choosing Gas Hot Water Size

Choosing the Cheapest Unit Only

A cheaper gas hot water system may be too small, the wrong gas type or unsuitable for the home.

Buying the Wrong Gas Type

Natural gas and LPG systems are different. Always confirm the correct gas type before ordering.

Comparing Litres and L/min Incorrectly

Gas storage is sized by litres and recovery rate. Instant gas is sized by flow rate in L/min. These are different measurements.

Ignoring Recovery Rate

For gas storage, recovery rate can be just as important as tank capacity.

Ignoring Flow Rate

For instant gas, flow rate is the key sizing factor. A lower-flow system may not suit a two-bathroom home.

Forgetting Gas Supply Suitability

A larger instant gas system still needs suitable gas supply.

Forgetting Water Pressure

Poor water pressure or flow may affect performance. A larger unit may not fix an underlying plumbing issue.

Forgetting Valves and Fittings

The main unit may not be the full order. Valves, pipework and fittings may also be required.

Gas Hot Water Size Buyer Checklist

Before ordering a gas hot water system online, check:

Current gas hot water system type
Current brand and model
Current tank capacity or flow rate
Whether the current system keeps up
Natural gas or LPG
Number of people in the home
Number of bathrooms
Number of showers per day
Whether two outlets may run together
Shower habits
Bath use
Kitchen hot water use
Laundry use
Desired system type
Tank capacity if gas storage
Recovery rate if gas storage
Flow rate in L/min if instant gas
Gas supply suitability
Water pressure and flow
Controller requirements if instant gas
Product dimensions
Connection positions
Outdoor or indoor model suitability
Required valves and fittings
Delivery access
Warranty information
Product specifications

Compare Gas Hot Water System Sizes Online

Hot Water Outlet makes it easier to compare gas hot water systems by type, brand, gas type, size, flow rate and product specifications.

Start with:

If your home does not have natural gas or LPG, compare electric hot water systems or heat pump hot water systems instead.

FAQs About Gas Hot Water System Size

What size gas hot water system do I need?

The right size depends on whether you are choosing gas storage or instant gas. Gas storage is sized by tank capacity and recovery rate. Instant gas is sized by flow rate in L/min.

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

Two people may suit a small to medium gas storage system or a 16 L/min to 20 L/min instant gas system depending on shower habits, bathroom count and whether hot water outlets overlap.

What size gas hot water system do I need for 3 people?

Three people usually need a medium gas storage system or a 20 L/min instant gas system where suitable. The right choice depends on bathrooms, bath use, shower habits and current system performance.

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

A family of 4 may need medium to larger gas storage or a 20 L/min to 26 L/min instant gas system depending on number of bathrooms, peak demand and gas supply suitability.

What size gas hot water system do I need for a family of 5?

A family of 5 or more often needs larger gas storage, stronger recovery or a 26 L/min instant gas system, especially where there are multiple bathrooms or heavy peak demand.

Is 16L gas hot water enough?

A 16 L/min instant gas system may suit smaller homes, units or lower-demand one-bathroom properties. It may not suit larger families or two-bathroom homes.

Is 20L gas hot water enough?

A 20 L/min instant gas system may suit moderate household demand, smaller families or homes where hot water use occasionally overlaps.

Is 26L gas hot water enough?

A 26 L/min instant gas system is commonly compared for larger homes, family households and two-bathroom properties. Gas supply, water pressure and product suitability still need to be confirmed.

Are natural gas and LPG hot water systems the same?

No. Natural gas and LPG systems are different and are not interchangeable. Always choose the model that matches the property’s gas type.

Can I install a gas hot water system myself?

No. Gas hot water systems involve gas and plumbing work that should be completed by appropriately licensed tradespeople. Hot Water Outlet sells supply-only hot water systems and accessories online, and may help organise quotes from reputable installers where appropriate.

Find the Right Size Gas Hot Water System

The right gas hot water system should match your household demand, gas type, number of bathrooms, available space and replacement setup. Before ordering, compare tank capacity, recovery rate, flow rate in L/min, natural gas or LPG model, dimensions, connection positions, warranty information and required accessories.

Browse gas hot water systems and instant gas hot water systems online with Hot Water Outlet to compare gas hot water options by brand, size, flow rate, gas type and product specifications.

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