Instant Gas vs Gas Storage Hot Water: Which Should You Choose?

Jul 2, 2026

Instant gas and gas storage hot water systems both use gas to heat water, but they work in very different ways. An instant gas system heats water as it flows through the unit. A gas storage system keeps a tank of hot water ready and reheats it with a gas burner.

The right choice depends on your household size, shower habits, bathroom count, gas supply, water pressure, installation location and whether your property uses natural gas or LPG.

This guide compares instant gas vs gas storage hot water, including sizing, running-cost considerations, recovery, installation checks and common mistakes to avoid before ordering.

Quick answer: instant gas vs gas storage hot water

System type	Best suited to	Main risk
Instant gas hot water	Homes wanting continuous hot water where gas pipe sizing and water flow suit	Poor performance if gas supply, water pressure or flow is not suitable
Gas storage hot water	Homes wanting stored hot water and simple replacement where an existing gas storage unit worked well	Tank can run out during high peak demand

An instant gas hot water system may be better where you want continuous hot water and the property has suitable gas pipework, water pressure and installation conditions.

A gas storage hot water system may be better where the existing gas storage setup works well, you want a stored hot water buffer, or a simple like-for-like replacement is preferred.

You can compare options in Gas Hot Water Systems, Instant Gas Hot Water Systems, or browse all Hot Water Systems.

What is instant gas hot water?

An instant gas hot water system heats water as it passes through the unit. It does not store hot water in a tank.

When a hot tap is opened, water flows through the heat exchanger and the gas burner heats the water on demand.

Instant gas systems are commonly sized by litres per minute, such as:

Instant gas size	Typical use
16L	Smaller homes, one bathroom, lower demand
20L	Small-to-medium homes, moderate demand
26L	Family homes, higher demand, two-bathroom homes where site conditions suit

The litre rating does not mean the system stores that amount of hot water. It is a flow-rate guide under test conditions. Real performance depends on gas supply, water pressure, flow rate, incoming water temperature and how many outlets are being used.

What is gas storage hot water?

A gas storage hot water system stores heated water in a tank and reheats it with a gas burner.

Common residential gas storage sizes include:

Gas storage size	Typical use
135L	Smaller homes, couples, moderate use
170L	Family homes, higher shower demand
Larger storage	Larger households or heavier demand

Gas storage systems keep hot water ready to use. Once the stored hot water is used, the burner reheats the tank. Gas storage usually recovers faster than many electric storage systems, but it can still run out if demand is high.

Instant gas vs gas storage comparison

Feature	Instant gas hot water	Gas storage hot water
How it works	Heats water as it flows through the unit	Stores hot water in a tank
Sizing method	Litres per minute, such as 16L, 20L or 26L	Tank size, such as 135L or 170L
Hot water supply	Continuous, subject to gas and water flow	Limited by stored volume and recovery
Space required	Usually wall-mounted and compact	Requires tank space
Best for	Continuous hot water where site conditions suit	Stored hot water and simpler like-for-like replacement
Main limitation	Needs suitable gas pipe sizing and water flow	Can run out during peak demand
Gas type	Natural gas or LPG model required	Natural gas or LPG model required
Installation complexity	Can be higher when changing from storage	Often simpler if replacing like-for-like
Power requirements	Some models need electrical connection	Model-dependent
Good for families	Yes, if correctly sized and supplied	Yes, if tank size and recovery suit

Which system gives more hot water?

Instant gas and gas storage provide hot water in different ways.

An instant gas system can keep heating water as long as the unit is operating correctly and the gas and water supply are suitable. It does not run out of stored water because there is no storage tank.

A gas storage system can deliver hot water from the tank quickly, but once the stored hot water is used, the household needs to wait for the burner to recover the tank.

For long back-to-back showers, instant gas may be more suitable. For homes that want a stored hot water buffer and where the old gas storage unit worked well, gas storage may be perfectly suitable.

Which system is better for families?

For family homes, both systems can work.

Instant gas may suit families where:

A 20L or 26L system is suitable
Gas pipe sizing is correct
Water pressure and flow are suitable
Multiple people shower close together
Continuous hot water is preferred
Tank space is limited

Gas storage may suit families where:

A 170L or larger tank is suitable
The old gas storage system performed well
The household wants stored hot water
The existing location suits another tank
A like-for-like replacement is preferred
Peak demand is not excessive

For larger families, system sizing matters more than system type alone.

Sizing instant gas hot water

Instant gas systems are usually sized by litres per minute.

16L instant gas

A 16L instant gas system may suit:

Small homes
One-bathroom properties
1–2 person households
Lower hot water demand
Like-for-like replacement where the old 16L unit worked well

It may be too small for families, long showers or homes where more than one hot water outlet is used at the same time.

20L instant gas

A 20L instant gas system may suit:

2–3 person homes
Moderate shower use
Small families
One main bathroom
Homes where 16L is too limited

It may still be tight for larger families, two bathrooms or heavy peak demand.

26L instant gas

A 26L instant gas system may suit:

Family homes
3–5 person households
Higher shower demand
Two-bathroom homes, subject to site conditions
Homes where a smaller instant gas unit struggled

A 26L system still needs suitable gas pipe sizing, water pressure, flow rate and installation location. Choosing 26L does not fix poor gas supply or poor water flow.

Sizing gas storage hot water

Gas storage systems are sized by tank capacity.

135L gas storage

A 135L gas storage system may suit:

1–2 person households
Smaller homes
Moderate shower use
Homes without large baths
Like-for-like replacement where the old 135L system worked well

It may be too small if multiple people shower back-to-back or the old system regularly ran out.

170L gas storage

A 170L gas storage system may suit:

3–5 person households
Family homes
Higher morning or evening demand
Back-to-back showers
Homes where 135L was marginal

A 170L gas storage unit gives more buffer than 135L and is often the safer storage choice for families.

Larger gas storage

Larger gas storage may suit:

Larger families
Homes with multiple bathrooms
Regular bath use
Shared homes
High-use households
Short-stay accommodation

Before choosing a larger gas storage system, check space, access, gas supply, water pressure, drainage and installation requirements.

Can instant gas run two showers?

A 26L instant gas system may be suitable for two-bathroom homes, but two-shower performance is not guaranteed in every property.

It depends on:

Shower flow rates
Incoming water temperature
Desired outlet temperature
Gas pipe sizing
Natural gas or LPG supply
Water pressure
Pipework condition
Distance to bathrooms
Whether other hot outlets are running

If the gas supply or water flow is poor, even a larger instant gas unit may not perform as expected.

Can gas storage run out?

Yes. Gas storage systems can run out if hot water is used faster than the tank can recover.

This may happen when:

Several showers happen back-to-back
Showers are long
The home has teenagers
A bath is filled
Guests are staying
Multiple bathrooms are used close together
The tank is undersized

Gas storage usually reheats faster than electric storage, but it still has a stored volume limit.

Natural gas vs LPG

Natural gas and LPG must be treated separately.

A gas hot water system must match the gas type available at the property. Natural gas models and LPG models are not interchangeable unless the manufacturer specifically allows conversion and the work is completed correctly by a licensed gas fitter.

Before ordering gas hot water, confirm:

Whether the property has natural gas or LPG
Whether the appliance matches the gas type
Whether the gas pipework is suitable
Whether the LPG bottle and regulator setup is suitable
Whether other gas appliances are connected
Whether installation clearances can be met
Whether a licensed gas fitter is completing the work

This is important for both instant gas and gas storage systems.

Gas pipe sizing is critical

Gas pipe sizing matters for all gas hot water systems, but it is especially important for instant gas.

A larger instant gas system may need more gas flow than an older storage unit or smaller instant gas unit. If the pipework is undersized, the system may struggle.

Possible signs of poor gas supply include:

Temperature fluctuations
Poor hot water performance
Burner issues
Fault codes
System cutting in and out
Other gas appliances being affected
Hot water not reaching the expected temperature

A licensed gas fitter should assess gas pipe sizing, especially when upgrading system size or changing from gas storage to instant gas.

Water pressure and flow matter

Instant gas systems need enough water flow to activate and maintain stable heating. Gas storage systems also need suitable water pressure and pipework to deliver hot water properly.

Important checks include:

Incoming water pressure
Shower flow rate
Pipework condition
Tempering valve condition
Mixer tap condition
Strainers or filters
Distance between the system and outlets
Whether multiple outlets are used at the same time

If only one tap or shower has poor hot water, the issue may be with that outlet, not the hot water system.

Temperature stability

Instant gas systems can provide stable hot water when correctly installed and supplied, but temperature issues can occur if the unit is undersized, the gas supply is poor, the water flow is inconsistent, or the system is not suited to the household’s usage.

Gas storage systems generally deliver from a stored tank, but outlet temperature can still be affected by tempering valves, pressure issues, pipework and mixer taps.

Temperature stability depends on the full installation, not just the appliance.

Space and location

Instant gas systems are usually wall-mounted and can save space compared with a storage tank. This can be useful where ground space is limited.

Gas storage systems require room for the tank, plus compliant access, drainage and clearances.

Before choosing either system, check:

Available wall or ground space
Access for installation and servicing
Clearances from openings and boundaries
Flueing or ventilation requirements where applicable
Water and gas connection locations
Electrical connection requirements
Drainage or relief valve discharge
LPG bottle location where relevant

A system that looks right on paper still needs to suit the actual installation location.

Recovery and peak demand

Instant gas does not recover in the same way as storage because it heats water as it flows. The key limit is whether the unit can produce enough hot water flow for the outlets being used.

Gas storage has stored water plus burner recovery. The key limit is whether the tank and burner can keep up with peak demand.

Usage pattern	Often better suited to
Long back-to-back showers	Instant gas, if gas and water supply suit
Smaller household with simple replacement	Gas storage
Limited tank space	Instant gas
Existing gas storage worked well	Gas storage
High simultaneous outlet demand	Larger instant gas or assessed option
Regular bath use	Larger storage or assessed option

Running-cost considerations

Running costs depend on more than system type.

Factors include:

Natural gas or LPG pricing
Supply charges
Household hot water use
Shower flow rates
System efficiency
Temperature settings
Storage heat loss
Instant gas activation and usage pattern
Pipe run length
Maintenance and age of system

Instant gas may reduce standing heat loss because it does not store hot water in a tank. Gas storage keeps water hot and may have storage losses. However, actual running costs depend heavily on usage and energy pricing.

LPG may cost more to run than natural gas depending on bottle pricing and household usage.

Instant gas pros and cons

Pros

Continuous hot water where correctly sized and supplied
No storage tank to run out
Usually compact and wall-mounted
Can suit homes with limited space
Often good for back-to-back showers
No stored tank heat loss

Cons

Needs suitable gas pipe sizing
Needs suitable water pressure and flow
May require electrical connection
Can struggle if multiple outlets exceed capacity
Temperature stability depends on site conditions
Changing from storage to instant may require extra work
Natural gas and LPG models must be selected correctly

Gas storage pros and cons

Pros

Stored hot water ready to use
Can be a simple like-for-like replacement
Fast recovery compared with many electric storage systems
Familiar system type
Can suit homes where existing gas storage worked well
Less sensitive to minimum flow than instant gas systems

Cons

Tank can run out during heavy use
Requires space for the storage tank
Has stored heat losses
May not suit homes with heavy back-to-back showers
Larger tanks need more space and access
Gas type and pipe sizing still need to be correct

Should I replace gas storage with instant gas?

Changing from gas storage to instant gas may make sense if:

You want continuous hot water
The old storage tank regularly ran out
Tank space is limited
The gas pipework can support the new unit
Water pressure and flow are suitable
The installation location is compliant
You are prepared for possible extra installation work

It may not make sense if:

Gas pipework is undersized
Water pressure or flow is poor
The existing gas storage system worked well
A simple replacement is preferred
The installation location does not suit an instant gas unit
Extra upgrade costs outweigh the benefit

A licensed installer should assess the site before changing system type.

Should I replace instant gas with gas storage?

Changing from instant gas to gas storage may make sense if:

The instant gas system has never performed well
Gas pipe sizing or water flow limits instant performance
The home has a suitable tank location
Stored hot water is preferred
A storage system better suits the household pattern
The installation can be completed compliantly

It may not make sense if:

There is no suitable tank space
Continuous hot water is important
The household has high back-to-back shower demand
The existing instant gas setup works well
Drainage or access for a storage tank is difficult

Instant gas vs gas storage for small households

For one or two-person homes, both options can work.

Instant gas may suit if:

Space is limited
Continuous hot water is preferred
Gas and water supply are suitable
The existing system is instant gas

Gas storage may suit if:

The existing gas storage system worked well
Hot water use is moderate
A 135L tank is suitable
A simple replacement is preferred

Small households should avoid oversizing unnecessarily, but the system still needs to suit the site and usage.

Instant gas vs gas storage for family homes

For families, the choice depends on peak demand.

Instant gas may suit if:

A 20L or 26L unit is suitable
Gas pipe sizing is adequate
Water pressure and flow are suitable
Multiple people shower close together
Continuous hot water is important

Gas storage may suit if:

A 170L or larger tank is suitable
The old storage system kept up
The household does not use excessive hot water at once
A like-for-like replacement is preferred

If the home has teenagers, multiple bathrooms or long showers, choose carefully.

Instant gas vs gas storage for rental properties

For rental properties, choose based on likely use, not just the lowest upfront cost.

Instant gas may suit rentals where:

Continuous hot water is a priority
The gas supply and water flow are suitable
The unit can be installed compliantly
Tank space is limited

Gas storage may suit rentals where:

The existing gas storage system is being replaced like-for-like
The tank size suits likely occupancy
The installation is straightforward
The property has suitable access and drainage

Undersized systems can cause repeated tenant complaints, regardless of type.

Brand options for gas hot water

Common gas hot water brands may include:

When comparing brands, check the system type, gas type, sizing, warranty terms, installation requirements, clearances, dimensions, controller options and whether the model suits your household.

Installation and compliance reminders

Gas hot water installation is not DIY work.

Use a licensed plumber and licensed gas fitter for gas hot water work. Electrical work, where required, must be completed by a licensed electrician.

Important installation checks may include:

Correct natural gas or LPG appliance
Gas pipe sizing
Water pressure and flow
Storage tank size or instant gas L/min rating
Tempering valve requirements
Isolation valves
Pressure relief valve discharge
Flueing or ventilation requirements where applicable
Appliance location and clearances
LPG bottle and regulator setup
Electrical connection where required
Safe access for installation and servicing
Compliance with current plumbing and gas requirements

Extra parts or site work may be required depending on the property. Relevant options may be available under Installation Add-Ons.

Supply-only vs supplied-and-installed

Installed Today offers gas hot water systems online with supply-only options across major metro areas.

For supply-only orders, you need to arrange your own suitable licensed installer. Gas hot water systems involve plumbing and licensed gas fitting, and some models may also involve electrical requirements.

Supplied-and-installed options are only available where shown in eligible Brisbane and Gold Coast service areas. Availability depends on the product, location and installation conditions shown at the time of ordering.

Before ordering, confirm the system type, gas type, size, installation location and any required add-ons.

Common mistakes when choosing instant gas vs gas storage

Comparing litres incorrectly

Instant gas litres per minute and gas storage tank litres are not the same thing. A 26L instant gas system is not the same as a 170L gas storage tank.

Choosing instant gas without checking gas pipe sizing

Instant gas needs suitable gas supply. Undersized pipework can cause poor performance.

Assuming gas storage cannot keep up

Gas storage can work well where the tank size and recovery suit the household.

Assuming instant gas always fixes running out

Instant gas avoids stored tank depletion, but it still has flow and gas supply limits.

Ordering the wrong gas type

Natural gas and LPG are not interchangeable. The appliance must match the property’s gas type.

Ignoring water pressure and flow

Poor water pressure or flow can affect both system types, especially instant gas.

Replacing like-for-like when the old system struggled

If the old system regularly ran out or performed poorly, choose the replacement around current demand and site suitability.

Forgetting installation extras

Gas upgrades, valves, drainage, electrical work, base work, controllers or access issues may affect the installation.

Final verdict

An instant gas hot water system is often the better option where the household wants continuous hot water and the property has suitable gas pipe sizing, water pressure, flow rate and installation conditions.

A gas storage hot water system is often the better option where the existing storage system worked well, a stored hot water buffer is preferred, or a simple like-for-like replacement is the most practical choice.

For small homes, a 135L gas storage system or 16L–20L instant gas system may be suitable. For family homes, a 170L gas storage system or 20L–26L instant gas system is usually the better starting point.

The right choice depends on household demand, bathroom count, natural gas or LPG supply, gas pipe sizing, water pressure, installation location and compliance requirements.

FAQs

Is instant gas better than gas storage?

Instant gas can be better where continuous hot water is wanted and the gas and water supply are suitable. Gas storage can be better where a stored hot water buffer and simple replacement are preferred.

Does instant gas run out of hot water?

Instant gas does not run out of stored hot water because it heats water on demand. However, it can still be limited by flow rate, gas supply, water pressure and simultaneous outlet use.

Does gas storage hot water run out?

Yes. Gas storage systems can run out if stored hot water is used faster than the burner can recover the tank.

What size instant gas hot water system do I need?

A 16L system may suit small homes, 20L may suit moderate-use homes, and 26L is commonly considered for family homes. The right size depends on flow rate, gas supply, water pressure and bathroom use.

What size gas storage hot water system do I need?

A 135L gas storage system may suit smaller households, while 170L is often better for family homes. Larger storage may be needed for high-use households.