Gas Hot Water Systems: Storage vs Instant Gas, Costs, Sizing and What to Choose

Gas hot water systems are a popular choice for Australian homes that already have natural gas or LPG available. They can heat water quickly, suit a wide range of household sizes and provide a familiar replacement path for homes already using gas hot water.

But not every gas hot water system is the same. A small gas storage tank, a 26L instant gas unit and a high-performance gas storage system all suit different homes. The right choice depends on your household size, gas type, water pressure, pipe sizing, installation location, hot water demand and whether you want a storage tank or continuous flow hot water.

For customers comparing products online, Installed Today’s Gas Hot Water Systems range is the best starting point. You can compare Instant Gas Hot Water Systems, 26L Instant Gas Hot Water Systems, 130/135L Gas Hot Water Systems, 160/170L Gas Hot Water Systems, Rinnai Hot Water Systems, Rheem Hot Water Systems and the full Hot Water Systems range before ordering.

Quick Answer

Best for simple gas storage replacement: 130L, 135L, 160L or 170L gas storage systems

Best for compact continuous flow hot water: instant gas hot water systems

Best for larger family homes: 26L instant gas or higher-performance gas storage, depending on the site

Main gas types: natural gas and LPG

Main thing to avoid: ordering the wrong gas type

Best first category: Gas Hot Water Systems

Best instant gas category: Instant Gas Hot Water Systems

Best larger instant gas category: 26L Instant Gas Hot Water Systems

Best alternative to compare: Heat Pump Hot Water Systems, especially if you want to move away from gas or use rooftop solar power

What Is a Gas Hot Water System?

A gas hot water system uses natural gas or LPG to heat water for showers, taps, kitchens, laundries and bathrooms.

There are two main types:

gas storage hot water systems
instant gas hot water systems

A gas storage system heats and stores water inside a tank. An instant gas system heats water only when a hot tap is turned on.

Both can be good options, but they suit different homes. Gas storage may be better for like-for-like tank replacement. Instant gas may be better if you want compact continuous flow hot water and the property has suitable gas supply, pipe sizing and water pressure.

Gas Storage Hot Water Systems

Gas storage hot water systems heat water with a gas burner and store it inside a tank. The system keeps stored hot water ready for use, then reheats the tank as hot water is used.

Gas storage may suit homes that:

already have a gas storage system
want a familiar tank-style replacement
use natural gas or LPG
have moderate daily hot water demand
prefer stored hot water over continuous flow
are replacing an older 130L, 135L, 160L or 170L gas tank
want a straightforward gas replacement where the existing location still suits

Common gas storage categories include 130/135L Gas Hot Water Systems and 160/170L Gas Hot Water Systems.

Gas storage may not be the best fit if you want a compact wall-mounted unit, want to remove the storage tank, or want the lowest running cost potential compared with heat pump hot water.

Instant Gas Hot Water Systems

Instant gas hot water systems, also called continuous flow gas systems, heat water as it passes through the unit. They do not store hot water in a tank.

When someone turns on a hot tap, water flows through the system, the gas burner activates and the water is heated on demand.

Instant gas may suit homes that:

already use natural gas or LPG
want a compact wall-mounted system
are replacing an existing continuous flow gas unit
do not want a storage tank
have suitable gas pipe sizing
have suitable water pressure
want continuous hot water while gas, water and power supply are suitable

Installed Today’s Instant Gas Hot Water Systems category includes common household sizes such as 16L, 20L and 26L systems.

For larger homes, 26L Instant Gas Hot Water Systems are often the main category to compare.

Natural Gas vs LPG

Gas type is one of the most important details when ordering a gas hot water system.

Natural gas and LPG are not interchangeable.

Natural gas systems are for homes connected to mains natural gas.

LPG systems are for homes using bottled gas.

Ordering the wrong gas type can delay installation, require a product swap or create extra costs.

Before ordering, check:

whether the home uses natural gas or LPG
what gas type the existing system uses
whether the selected product is available in that gas type
whether the gas supply can support the selected model
whether a licensed gas fitter has confirmed suitability

This matters for both gas storage and instant gas systems.

Gas Storage vs Instant Gas: Which Is Better?

There is no single winner. Gas storage and instant gas suit different homes.

Gas storage is usually better when:

the existing system is already gas storage
the household wants a familiar tank-style replacement
the current tank size worked well
the installation location suits a storage tank
the household prefers stored hot water
upfront simplicity is important

Instant gas is usually better when:

the household wants a compact wall-mounted unit
the home already has suitable gas supply and pipe sizing
the customer wants continuous flow hot water
the existing system is already instant gas
the customer wants to remove the storage tank
space is limited

If you are unsure, compare both options inside Installed Today’s Gas Hot Water Systems range.

What Size Gas Hot Water System Do You Need?

The right size depends on system type.

For gas storage, size is based on tank capacity and recovery. Common options include 130L, 135L, 160L and 170L storage systems, along with higher-performance models.

For instant gas, size is based on flow rate, usually shown in litres per minute. Common options include 16L, 20L and 26L instant gas systems.

A small household may not need a 26L instant gas system. A larger household may not be happy with a compact gas storage tank. The right choice depends on how much hot water the household uses and how many outlets may be used at the same time.

Consider:

number of people in the home
number of bathrooms
shower length
bath use
kitchen and laundry use
morning and evening peak demand
whether multiple showers may run at once
whether the old system supplied enough hot water
existing gas pipe sizing
water pressure
incoming cold water temperature

If the old system was always running out of hot water, replacing it with the same size may repeat the problem.

16L, 20L and 26L Instant Gas Systems

Instant gas systems are often compared by flow size.

A 16L instant gas system may suit smaller homes, units, granny flats or lower hot water demand.

A 20L instant gas system may suit small to medium households with moderate use.

A 26L instant gas system may suit medium to larger households, especially homes with higher shower demand or more than one bathroom.

That said, bigger is not automatically better. A 26L system needs suitable gas supply, pipe sizing and water pressure to perform properly.

A poorly supported 26L unit may not deliver the result the customer expects if the property’s gas infrastructure cannot keep up.

130L, 135L, 160L and 170L Gas Storage Systems

Gas storage systems are commonly chosen for like-for-like replacement.

A 130L or 135L gas storage system may suit:

small to medium households
townhouses
rental properties
homes with one main bathroom
moderate daily hot water use
properties replacing a similar-size gas tank

A 160L or 170L gas storage system may suit:

larger households
homes with higher daily demand
more frequent showers
properties where a 135L tank may not be enough
households wanting extra stored capacity

For compact gas storage, start with 130/135L Gas Hot Water Systems. For larger storage, compare 160/170L Gas Hot Water Systems.

Popular Gas Hot Water Brands

Gas hot water systems are available from well-known brands such as Rinnai, Rheem, Vulcan, Bosch, Aquamax and Dux.

Rinnai is commonly compared for instant gas and continuous flow systems. Installed Today’s Rinnai Hot Water Systems collection is a useful starting point for Rinnai gas options.

Rheem is commonly compared for gas storage, gas continuous flow and broader hot water options. Installed Today’s Rheem Hot Water Systems collection is useful for Rheem comparisons.

Vulcan is often compared for practical value-focused gas storage options. Installed Today’s Vulcan Hot Water Systems collection is useful if you want a straightforward replacement option.

Dux and Aquamax may also be worth comparing where the model, availability and household demand suit.

Rinnai Gas Hot Water Systems

Rinnai is one of the most common names in continuous flow gas hot water. Models such as 16L, 20L and 26L instant gas systems are often compared by households replacing older external gas units.

Rinnai may suit customers who:

want a recognised instant gas brand
are replacing an existing Rinnai unit
want natural gas or LPG options
prefer compact continuous flow hot water
need a 16L, 20L or 26L system
have suitable gas supply and pipe sizing

For larger family homes, compare 26L Instant Gas Hot Water Systems and the broader Rinnai Hot Water Systems collection.

Rheem Gas Hot Water Systems

Rheem is a major hot water brand with gas storage and continuous flow options.

Rheem may suit customers who:

prefer a well-known hot water brand
are replacing an older Rheem system
want gas storage or continuous flow gas
need a premium storage option
want natural gas or LPG options
are comparing gas against electric or heat pump systems

Rheem gas storage systems may be especially relevant for homes wanting strong stored hot water performance, while Rheem continuous flow systems may suit customers comparing Rinnai-style instant gas alternatives.

Start with Rheem Hot Water Systems or the broader Gas Hot Water Systems range.

Vulcan Gas Hot Water Systems

Vulcan gas hot water systems are often chosen for simple, value-focused replacement.

Vulcan may suit customers who:

want a practical gas storage replacement
are replacing an older compact gas tank
need natural gas or LPG options
are buying for a rental property
want straightforward operation
do not need a premium gas storage model

Vulcan is worth comparing against Rheem and Rinnai if the priority is a practical replacement rather than the highest-performance system.

Browse Vulcan Hot Water Systems for current options.

Gas Hot Water vs Electric Hot Water

Gas hot water and electric hot water suit different homes.

Gas may be better when:

the home already has natural gas or LPG
the customer wants fast recovery
the existing system is gas
the household wants instant gas continuous flow
the installation location already suits gas hot water

Electric may be better when:

gas is not available
the customer wants a simple storage tank
the home already has electric storage
the upfront budget is limited
the site is not suitable for gas installation

For broader comparison, Installed Today’s Electric Hot Water Systems category is worth reviewing alongside gas options.

Gas Hot Water vs Heat Pump Hot Water

Heat pump hot water is the main alternative to consider if the goal is lowering running costs or moving away from gas.

A gas hot water system may be better when:

the home already has gas
the customer wants compact instant gas
the existing gas system worked well
the property has suitable gas pipework
the household wants familiar gas hot water

A heat pump may be better when:

the home has rooftop solar
the customer wants to reduce gas use
there is suitable outdoor space
airflow and drainage are available
noise placement can be managed
the customer wants lower running cost potential than standard electric storage

Installed Today’s Heat Pump Hot Water Systems, Medium Heat Pump Hot Water Systems 200L–280L and Large Heat Pump Hot Water Systems categories are useful if you are comparing gas with efficient electric upgrades.

Gas Hot Water Running Costs

Gas hot water running costs depend on more than the system type.

They are affected by:

natural gas or LPG pricing
daily hot water use
number of people in the home
shower length
flow rate
system size
temperature settings
storage heat loss
pipe length
maintenance condition
gas supply setup

Instant gas systems only heat water when a tap is running, while gas storage systems keep a tank of water hot. This can affect running costs, but the result depends on household use and the specific product.

LPG can also cost more than natural gas depending on bottle pricing, delivery and usage, so customers using LPG should compare carefully.

Installation Requirements for Gas Hot Water

Gas hot water installation should always be handled by licensed professionals.

A proper installation needs to consider:

gas type
gas pipe sizing
water pressure
installation location
clearances
ventilation
flue requirements if relevant
pipework alignment
valve requirements
tempering valve requirements
drainage and discharge points
controller wiring if relevant
old unit removal
compliance requirements

A gas hot water system may look like a simple swap, but the existing installation may not meet current requirements. This can affect the final cost and installation pathway.

Supply Only vs Supplied and Installed

Installed Today offers supply-only ordering for customers who already have their own licensed installer arranged. Supply-only pricing is for the product only and does not include installation, valves, gas work, electrical work, pipework changes, drainage work, old unit removal, disposal, wall mounting changes or compliance upgrades unless those options are clearly selected or shown on the product page.

Supplied-and-installed options may be available on selected products in eligible Brisbane and Gold Coast service areas. Availability depends on the product, location, gas type, access, existing setup, gas supply, pipe sizing, water pressure, required extras and site requirements.

Before ordering supply only, make sure your licensed gas fitter has confirmed the correct gas type, model size, installation location, pipe sizing, controller requirements and compliance needs.

Brisbane and Gold Coast Buying Context

For Brisbane and Gold Coast homes, gas hot water systems are commonly chosen for like-for-like replacements, especially where the property already uses natural gas or LPG.

Local homes should check:

whether the property uses natural gas or LPG
whether the existing system is gas storage or instant gas
whether the old system supplied enough hot water
whether gas pipe sizing is suitable
whether water pressure is suitable
whether the unit location meets clearance requirements
whether valves need replacing
whether controller changes are required
whether access allows safe removal and installation
whether supplied-and-installed is available for the address
whether heat pump hot water should be compared

A gas system can be practical, but it still needs to match the home.

Common Gas Hot Water Problems

Common gas hot water problems include:

no hot water
hot water cutting in and out
temperature fluctuation
pilot light issues on storage systems
fault codes on instant gas systems
low flow problems
blocked inlet filters
gas supply issues
incorrect gas type
undersized pipework
valve leaks
relief valve discharge
burner or thermostat faults
controller problems

Some issues are product-related, but many are site-related. Gas supply, pipe sizing, water pressure, valves, controllers and installation clearances can all affect performance.

Gas hot water repairs should only be handled by licensed professionals.

Gas Hot Water Maintenance

Gas hot water systems are not maintenance-free.

Maintenance may include:

checking for visible leaks
checking valves
monitoring relief valve discharge
checking burner operation
checking pilot operation on storage systems
watching for fault codes
cleaning filters where required by a licensed technician
checking controllers
keeping clearances unobstructed
servicing according to manufacturer guidance

Regular maintenance can help reduce breakdown risk, improve performance and identify issues before they become bigger problems.

Before Ordering Checklist

Before ordering a gas hot water system, check:

natural gas or LPG
current system type
current system size
household size
bathroom count
shower habits
whether the old system supplied enough hot water
gas pipe sizing
water pressure
installation location
wall space or tank space
clearance requirements
valve requirements
controller requirements
drainage and discharge points
access for removal and delivery
supply-only or supplied-and-installed preference
licensed installer confirmation

This helps avoid ordering the wrong gas type, wrong size or wrong system for the property.

Which Gas Hot Water System Should You Choose?

Choose gas storage if you want a familiar tank-style gas replacement and the old storage system worked well.

Choose instant gas if you want compact continuous flow hot water and the property has suitable gas supply and pipe sizing.

Choose a 26L instant gas system if the household has higher demand and the property can support it.

Choose a 130L or 135L gas storage system if the household has moderate demand and wants a compact storage replacement.

Choose a 160L or 170L gas storage system if the household needs more stored hot water than a compact tank can provide.

Compare heat pump hot water if your main goal is lowering running costs or moving away from gas.

For most customers, the safest starting point is Installed Today’s Gas Hot Water Systems collection, then narrowing down by gas type, system style, size and installation requirements.

Long-Tail FAQs

What are the main types of gas hot water systems?

The two main types are gas storage and instant gas. Gas storage systems heat and store water in a tank. Instant gas systems heat water as it flows through the unit when a tap or shower is turned on.

Is instant gas better than gas storage?

Instant gas may be better if you want a compact wall-mounted system and continuous flow hot water. Gas storage may be better if you want a familiar tank-style replacement and the existing storage system worked well. The best choice depends on the property.

Is natural gas the same as LPG?

No. Natural gas and LPG systems are different and must be ordered correctly. A natural gas unit should not be installed on LPG, and an LPG unit should not be installed on natural gas.

What size instant gas hot water system do I need?

The right size depends on household demand, number of bathrooms, shower flow rates, incoming water temperature, gas supply and pipe sizing. A 26L system may suit many larger homes, but the property must be able to support it.

Is a 135L gas storage system enough for a family?

A 135L gas storage system may suit some small to medium households with moderate use. Larger families, long showers, bath use or multiple bathrooms may need a larger storage system or an instant gas option.

Is gas hot water cheaper than electric hot water?

Gas can be cheaper to run in some homes, especially where natural gas is available and usage suits the system. However, running costs depend on gas tariffs, LPG bottle costs, usage, system type and maintenance. Heat pump hot water should also be compared if running cost reduction is the main goal.

Can I replace electric hot water with gas?

It may be possible, but it can involve extra plumbing, gas fitting, compliance checks, gas supply confirmation and possibly electrical work. The final decision depends on whether the property has natural gas or LPG available and whether the installation cost makes sense.

Can I buy a gas hot water system supply only?

Yes. Supply only is suitable if you already have your own licensed plumber or gas fitter arranged. The product price is for the unit only and does not include installation, gas work, valves, disposal, pipework changes or compliance upgrades unless selected separately.

Can I order a gas hot water system supplied and installed?

Supplied-and-installed options may be available on selected products in eligible Brisbane and Gold Coast service areas. Availability depends on the address, gas type, access, existing setup, pipe sizing, water pressure and required extras.

What is the biggest mistake when choosing gas hot water?

The biggest mistake is ordering by product price alone without confirming gas type, sizing, gas pipework, water pressure, installation location and household hot water demand.

Final Word

Gas hot water systems can be a strong choice for homes already using natural gas or LPG. Gas storage suits customers who want familiar tank-style hot water, while instant gas suits homes wanting compact continuous flow hot water.

The right system depends on gas type, household demand, pipe sizing, water pressure, installation location and whether the existing system was actually doing the job properly.

Before ordering, compare Installed Today’s Gas Hot Water Systems, Instant Gas Hot Water Systems, 26L Instant Gas Hot Water Systems, Rinnai Hot Water Systems, Rheem Hot Water Systems and full Hot Water Systems range to find the best fit for your home.