Gas Storage Hot Water Size Guide: 135L vs 170L vs Larger Gas Storage Systems

Choosing the right gas storage hot water size is not just about picking the same litre capacity you already have. Gas storage systems heat and recover differently to electric storage systems, so a smaller gas storage tank can sometimes keep up better than a larger electric unit, depending on household use.

For most homes, the common gas storage choices are around 135L, 170L, and larger-capacity gas storage systems. The right size depends on how many people live in the home, how many showers run close together, whether you have baths, and whether the system is running on natural gas or LPG.

This guide explains how to choose between 135L, 170L and larger gas storage hot water systems, what to check before replacing your old unit, and when another system type may be a better fit.

Quick answer: what size gas storage hot water system do I need?

As a general guide:

A 135L gas storage hot water system can suit smaller homes and moderate-use households. A 170L gas storage hot water system is often a better fit for families or homes with higher peak demand. Larger systems may be needed where multiple people shower back-to-back, baths are used regularly, or the home has high hot water usage.

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

Gas storage sizing is different to electric storage sizing

Gas storage and electric storage hot water systems are not sized exactly the same way.

Electric storage systems rely heavily on tank volume because they usually recover more slowly, especially if they are connected to an off-peak or controlled-load tariff. A home that runs out of hot water from an undersized electric tank may need a much larger electric storage unit.

Gas storage systems usually reheat faster. That means the usable performance is not only about tank size. Recovery rate matters.

For example, a 135L gas storage unit may serve some homes better than a larger electric unit because it can reheat water more quickly during the day. But that does not mean 135L suits every family. If the household has long showers, multiple bathrooms, or heavy morning demand, a 170L or larger option may still be the better choice.

What is a gas storage hot water system?

A gas storage hot water system stores hot water in a tank and uses a gas burner to reheat the water as it is used. Unlike an instant gas system, it does not heat water only as it flows through the unit. It keeps a stored volume of hot water ready for use.

Gas storage systems are commonly used where the property already has:

• Natural gas connected, or

• LPG bottles installed and suitable for hot water use

Gas storage hot water can be a practical option where the existing system is already gas storage and the gas supply, location, flueing, drainage and water connections are suitable.

Natural gas and LPG are not interchangeable. The appliance must match the available gas type, and any gas work must be completed by a licensed gas fitter.

135L gas storage hot water systems

A 135L gas storage hot water system is one of the most common small-to-mid household gas storage sizes.

Best suited to

A 135L gas storage system may suit:

• 1–2 person homes

• Small townhouses or units where gas storage is already installed

• Moderate shower use

• Homes without large baths

• Households where hot water demand is spread out

• Like-for-like replacement where the old 135L unit performed well

Advantages of 135L gas storage

The main advantages are:

• Smaller footprint than larger storage systems

• Generally easier to position where space is limited

• Often suitable for smaller households

• Faster recovery than many electric storage systems

• Good option where existing gas storage connections are already suitable

For smaller households, a 135L system can be enough when showers are normal length and hot water is not being heavily used at the same time by multiple outlets.

When 135L may be too small

A 135L gas storage unit may struggle if:

• 3–4 people shower close together every morning

• The home has teenagers or long showers

• A bath is filled regularly

• Multiple bathrooms are used at once

• The previous system often ran out

• Guests regularly stay at the property

If the old 135L unit did not keep up, replacing it with another 135L may repeat the same problem. In that case, stepping up to 170L or considering another system type may be smarter.

170L gas storage hot water systems

A 170L gas storage hot water system is often the safer choice for family homes.

Best suited to

A 170L gas storage system may suit:

• 3–5 person households

• Homes with higher morning or evening hot water demand

• Families with children or teenagers

• Homes with two bathrooms

• Properties where the old 135L system was marginal

• Homes wanting more stored hot water without moving to a very large tank

Advantages of 170L gas storage

The main advantage of moving from 135L to 170L is extra buffer.

That extra stored hot water can help during peak periods, especially when multiple showers happen close together. It can also reduce complaints about the system running out after the first few showers.

A 170L system may be a better fit where the home does not need a very large storage unit, but 135L feels too tight.

When 170L may still not be enough

A 170L gas storage system may still be undersized if:

• 5 or more people live in the home

• Several long showers happen back-to-back

• Large baths are used frequently

• Multiple bathrooms are used at the same time

• The household has unusually high hot water use

• The property is used as short-stay accommodation

In those cases, a larger storage system, an Instant Gas Hot Water System, or another hot water type may be worth considering.

Larger gas storage hot water systems

Larger gas storage systems are used where the home needs more stored hot water capacity than a standard 135L or 170L unit can comfortably provide.

Best suited to

Larger gas storage may suit:

• Larger families

• Homes with multiple bathrooms

• Homes with frequent bath use

• Properties with high peak demand

• Shared households

• Some rental or short-stay properties with higher usage patterns

Things to check before choosing larger gas storage

Before increasing tank size, check whether the property can actually support the larger unit.

Important checks include:

A larger tank is not always the best answer. Sometimes the real issue is poor shower flow, a faulty tempering valve, undersized gas supply, or an old system that is not recovering properly.

135L vs 170L gas storage hot water

Should I replace like-for-like?

Replacing like-for-like can make sense if the old gas storage system worked well before it failed.

For example, if a 135L gas storage system served a two-person home without running out, another 135L system may be fine.

But like-for-like replacement is not always the right move. You should rethink the size if:

• The old unit regularly ran out of hot water

• More people now live in the home

• A second bathroom has been added

• The household has changed shower habits

• The old system was very old and no longer performing properly

• You are switching from electric to gas or gas to another system type

If the home’s hot water use has changed, the replacement system should be chosen around current demand, not just the model that was already there.

Gas storage vs instant gas hot water

Gas storage and instant gas systems work differently.

Instant gas systems are usually sized in litres per minute, such as 16L, 20L or 26L. A 26L instant gas system is commonly considered for larger homes, but it must be assessed properly. Gas pipe sizing, water pressure, gas type, controller setup and outlet demand all matter.

If you are comparing system types, view Instant Gas Hot Water Systems alongside Gas Hot Water Systems.

Gas storage vs electric storage hot water

Gas storage and electric storage systems also perform differently.

If the property does not have suitable gas, or if you are comparing running costs and efficiency, it may be worth looking at Electric Hot Water Systems or Heat Pump Hot Water Systems.

Natural gas vs LPG for gas storage hot water

Natural gas and LPG must be treated separately.

A gas storage hot water system is built and certified for a specific gas type. You cannot assume a natural gas model can be connected to LPG, or that an LPG model can be connected to natural gas.

Before ordering, confirm:

• The available gas type

• The appliance gas type

• Whether the existing gas supply is suitable

• Whether LPG bottle location and regulator setup are suitable

• Whether the gas pipework is correctly sized

• Whether a licensed gas fitter is completing the work

This matters for safety, performance and compliance.

How shower habits affect gas storage size

Hot water sizing is not just about the number of people in the house.

A two-person home with long showers can use more hot water than a four-person home with short showers. A family with teenagers may need more hot water than the same number of adults with shorter usage patterns.

Key usage questions:

• How many showers happen back-to-back?

• How long are the showers?

• Are multiple bathrooms used at once?

• Is there a large bath?

• Do guests stay regularly?

• Is hot water used heavily for cleaning, laundry or other tasks?

• Did the old system run out often?

If hot water demand happens in one heavy peak period, choose more carefully. Stored hot water systems need enough usable volume and recovery to get through that peak.

Common gas storage size scenarios

Small unit or townhouse

A 135L gas storage system may be enough where one or two people live in the home and shower use is moderate.

Couple with occasional guests

A 135L system may still work, but a 170L system gives more buffer if guests stay regularly.

Family of four

A 170L gas storage system is often the better starting point, especially where showers happen close together.

Family of five or more

A 170L system may work in some homes, but larger storage or another system type may be more suitable if demand is heavy.

Rental property

Choose based on likely occupant use, not just the lowest upfront cost. Undersized systems can create repeat complaints.

Short-stay accommodation

Consider peak demand carefully. Guests may use more hot water than a normal household, especially with multiple bathrooms.

Installation and compliance reminders

Gas storage hot water installation is not a DIY job.

A licensed plumber or gas fitter must handle the required plumbing and gas work. Electrical work, where required, must be completed by a licensed electrician.

Important installation items may include:

• Correct gas type selection

• Gas pipe sizing check

• Water pressure assessment

• Tempering valve requirements

• Isolation valves

• Pressure relief valve discharge

• Safe tray or drainage where required

• Compliant clearances

• Flueing or ventilation requirements where applicable

• Access for removal and installation

• LPG regulator and bottle setup where relevant

If extra parts or site work are required, they may need to be selected separately through Installation Add-Ons.

Supply-only vs supplied-and-installed

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

For supply-only orders, you need to arrange your own suitable licensed installer. This is especially important for gas storage hot water systems because gas fitting and plumbing must be done by licensed trades.

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.

Do not order a gas storage system assuming it can be installed anywhere or by anyone. Confirm the correct gas type, size and installation requirements before purchase.

Common mistakes when choosing gas storage size

Choosing the same size even though it always ran out

If the old system regularly ran out, replacing it with the same size may not solve the issue.

Comparing gas storage litres directly to electric storage litres

A 135L gas storage system does not perform the same way as a 135L electric storage system. Recovery rate matters.

Ignoring shower flow

High-flow showers use stored hot water faster. Multiple high-flow showers can overwhelm a smaller tank.

Forgetting about baths

A large bath can use a major portion of stored hot water. If the home uses baths often, size up carefully.

Ordering the wrong gas type

Natural gas and LPG are not interchangeable. Always choose the correct appliance type.

Assuming gas pipework is suitable

Some replacements may need gas pipe sizing checked, especially when changing system type or increasing demand.

Forgetting valves and installation extras

Older systems may need valves, drainage upgrades, base work or other installation items. Check relevant add-ons before ordering.

Final verdict

For smaller households, a 135L gas storage hot water system can be a practical and efficient choice where hot water use is moderate and the existing gas setup is suitable.

For family homes, a 170L gas storage hot water system is often the safer choice because it gives more stored hot water buffer during busy morning and evening periods.

For larger households, homes with multiple bathrooms, or properties with heavy hot water demand, consider larger gas storage, Instant Gas Hot Water Systems, or another suitable system type.

The best size is not just the tank capacity. It depends on household demand, gas type, recovery rate, water pressure, gas pipe sizing, installation location and compliance requirements.

FAQs

Is a 135L gas hot water system enough for a family?

A 135L gas storage system may be enough for a small family with moderate shower use, but it can be tight for families with long showers or back-to-back bathroom use. A 170L system is often a safer option for family homes.

Is 170L gas storage enough for four people?

A 170L gas storage hot water system is commonly considered for four-person households, but it depends on shower length, bath use and how closely hot water is used together.

Can I replace a 135L gas storage system with a 170L system?

Often yes, but it depends on the installation location, space, gas supply, pipework, drainage and model suitability. A licensed installer should check the site before installation.

Does gas storage recover faster than electric storage?

Gas storage systems generally recover faster than many electric storage systems. That is why gas storage sizing should not be compared only by tank litres.

What happens if my gas storage system is too small?

You may run out of hot water during peak use, especially when several showers happen close together. The system may recover later, but it may not keep up during busy periods.

What happens if my gas storage system is too large?

An oversized system may cost more upfront, take up more space and store more hot water than the household needs. The right size should match actual usage.

Should I choose gas storage or instant gas?

Gas storage may suit homes where a like-for-like replacement is simple and stored hot water works well. Instant gas may suit homes wanting continuous hot water, but gas pipe sizing, flow rate and installation conditions must be checked.

Can I use LPG for a gas storage hot water system?

Yes, but only with an LPG-compatible appliance and suitable LPG setup. Natural gas and LPG models are not interchangeable.

Do I need a licensed gas fitter?

Yes. Gas storage hot water installation requires licensed gas fitting and plumbing work. Electrical work, where required, must also be completed by a licensed electrician.

Where can I compare gas storage hot water systems?

You can compare options in Gas Hot Water Systems or browse broader Hot Water Systems.