Instant Gas Hot Water System Replacement Cost: Australian Buyer’s Guide

Jun 20, 2026

Replacing an instant gas hot water system can be a practical upgrade for homes that already use natural gas or LPG and want compact continuous flow hot water. Unlike gas storage systems, instant gas units do not keep a tank of hot water heated all day. They heat water as it passes through the unit, which can make them a strong option for many homes, townhouses, rentals and renovations.

However, instant gas replacement cost can vary a lot depending on the existing setup. A simple like-for-like swap is usually much easier than changing from gas storage to instant gas, upgrading to a larger flow rate, moving the unit, changing gas pipework, adding controllers, or converting from electric hot water.

This guide explains what affects instant gas hot water system replacement cost, how instant gas compares with gas storage, electric and heat pump hot water, and what to check before ordering.

You can compare Instant Gas Hot Water Systems, Gas Hot Water Systems, broader Hot Water Systems, Electric Hot Water Systems and Heat Pump Hot Water Systems online with Installed Today.

Quick answer: what affects instant gas hot water replacement cost?

Instant gas hot water replacement cost depends on the product, gas type, flow rate and installation requirements.

The main cost factors include:

Brand and model
Flow rate in litres per minute
Natural gas or LPG
Existing hot water system type
Gas pipe sizing
Water pressure
Electrical power point availability
Installation location
Outdoor clearances
Controller requirements
Pipework changes
Old unit removal
Disposal
Access
Compliance upgrades
Whether replacing like-for-like or changing system type

The cheapest instant gas unit is not always the cheapest replacement if the home needs gas pipework, electrical work, controller wiring or relocation.

What is an instant gas hot water system?

An instant gas hot water system heats water only when a hot tap is turned on.

Cold water flows through the unit, gas burners heat the water as it passes through, and hot water is delivered to taps and showers.

Instant gas systems are also called:

Continuous flow gas hot water systems
Tankless gas hot water systems
Instantaneous gas hot water systems
Gas continuous flow systems

They are different from gas storage systems because they do not store a tank of hot water.

How instant gas hot water works

A simple instant gas process looks like this:

A hot tap or shower is turned on
Water flows through the instant gas unit
The unit detects water flow
Gas burners ignite
Water is heated as it passes through the heat exchanger
Hot water travels through the pipework to the outlet
The burner turns off when hot water demand stops

Instant gas systems need the right combination of gas supply, water pressure, flow rate, power where required, and correct installation.

Instant gas vs gas storage replacement cost

Instant gas and gas storage systems have different cost factors.

Feature	Instant gas hot water	Gas storage hot water
Hot water style	Continuous flow	Stored hot water
Tank	No storage tank	Storage tank required
Space	Compact wall-mounted unit	More space required
Gas supply	Required	Required
Gas pipe sizing	Often critical	Important
Water pressure	Very important	Important
Electrical power	Often required	Depends on model
Replacement risk	Gas pipe sizing, power, mounting, flow rate	Tank size, base, valves, disposal
Best suited to	Compact gas hot water	Stored gas hot water replacement

A like-for-like instant gas replacement is usually simpler than changing from storage to instant gas.

Like-for-like instant gas replacement

A like-for-like instant gas replacement may be more straightforward when:

The old unit was also instant gas
The new unit has a similar flow rate
The gas type stays the same
The location stays the same
Gas pipe sizing is suitable
Water pressure is suitable
A power point is already available where needed
Pipework lines up reasonably well
Clearances are suitable
Access is easy
The old unit can be removed easily

Even then, a licensed gas fitter should confirm the new unit suits the property.

Replacing gas storage with instant gas

Changing from gas storage to instant gas can be a worthwhile upgrade for some homes, but it is not always a simple swap.

Extra work may include:

Removing the old storage tank
Wall mounting the new instant gas unit
Changing pipework
Checking gas pipe sizing
Adding or changing electrical power
Installing controllers where selected
Checking water pressure
Changing drainage or discharge setup
Confirming outdoor clearances
Completing compliance work

Instant gas is compact, but it often needs stronger gas supply than older gas storage systems.

Replacing electric hot water with instant gas

Changing from electric hot water to instant gas can be more complex than replacing like-for-like.

Extra requirements may include:

Natural gas or LPG supply
Licensed gas fitting
New gas pipework
New outdoor location
Water pipework changes
Electrical disconnection or changes
Power point for the gas unit where needed
Old electric tank removal
Disposal
Compliance upgrades

If the home does not already have suitable gas, compare Heat Pump Hot Water Systems before committing to a gas conversion.

Replacing heat pump hot water with instant gas

Changing from heat pump hot water to instant gas is possible where the property has suitable gas supply, but it is a major system-type change.

You may need to check:

Natural gas or LPG availability
Gas pipe sizing
Outdoor mounting location
Water pipework changes
Electrical power
Removal of the heat pump tank
Disposal
Hot water demand
Whether continuous flow suits the household
Whether gas remains the preferred long-term energy source

This is usually more involved than replacing heat pump with heat pump or instant gas with instant gas.

Natural gas vs LPG instant gas cost factors

Natural gas and LPG are not interchangeable.

Before ordering any instant gas hot water system, confirm:

Whether the property uses natural gas or LPG
Whether the selected model matches the property gas type
Whether the existing unit label confirms the gas type
Whether LPG bottles or natural gas meter setup is suitable
Whether gas pipe sizing supports the selected flow rate
Whether your licensed gas fitter has confirmed compatibility

Ordering the wrong gas type can delay replacement and add cost.

Instant gas flow rate and replacement cost

Instant gas systems are often compared by flow rate, usually measured in litres per minute.

Common categories include:

16L instant gas
20L instant gas
26L instant gas

A larger flow rate may cost more and may need more gas supply.

The right flow rate depends on:

Number of bathrooms
Number of showers
Whether two showers run at once
Shower head flow rates
Distance from unit to outlets
Water pressure
Gas pipe sizing
Natural gas or LPG
Household habits

A larger unit does not guarantee better performance if the gas supply or water pressure cannot support it.

16L instant gas replacement

A 16L instant gas system may suit lower-demand homes where only one shower or outlet is likely to be used at a time.

It may suit:

Smaller homes
Units or townhouses where gas setup suits
One-bathroom homes
Low-to-moderate hot water use
Some rental properties
Customers replacing a similar low-flow instant gas unit

Before choosing 16L, check household demand carefully. It may not suit homes that want multiple showers running at once.

20L instant gas replacement

A 20L instant gas system may suit many moderate-demand homes.

It may be considered for:

Small to medium households
One to two bathroom homes with moderate use
Homes replacing an existing 20L unit
Properties with suitable gas pipe sizing
Customers wanting continuous flow hot water without a tank

Before choosing 20L, confirm shower habits, water pressure and gas supply.

26L instant gas replacement

A 26L instant gas system is often compared by larger households or homes with two bathrooms.

It may suit:

Larger families
Two-bathroom homes
Homes with higher hot water demand
Customers wanting stronger continuous flow capacity
Properties replacing an existing 26L unit
Homes with suitable gas pipe sizing and water pressure

A 26L system can be a strong option, but the property must support it. Gas pipe sizing and water pressure matter.

Gas pipe sizing cost factors

Gas pipe sizing is one of the biggest instant gas replacement cost factors.

Cost can increase if:

The existing pipe is too small
The new unit has a higher flow rate
The pipe run is long
Other gas appliances share the supply
The old system was gas storage
The new unit needs more gas input
Pipework needs to be upgraded for compliance

Poor gas supply can affect instant gas performance, so it should be checked before choosing the unit.

Water pressure cost factors

Instant gas systems need suitable water flow and pressure.

Cost or performance issues may occur if:

Water pressure is too low
Pipework is restricted
Fixtures have flow issues
Multiple outlets are used at once
Old valves restrict flow
Pressure control needs attention
The selected unit requires more flow than the property can provide

If hot water pressure has been poor, diagnose the cause before replacing the system.

Electrical cost factors

Many instant gas systems require electrical power for ignition, fan operation, controls or freeze protection depending on model.

Cost may increase if:

No power point is nearby
A new weatherproof power point is needed
Electrical work is required
The unit is being relocated
Controller wiring is needed
Old wiring does not suit the new setup

A licensed electrician may be required depending on the job.

Controller cost factors

Some instant gas systems can use temperature controllers.

Controllers may add cost through:

Controller purchase
Wiring
Wall mounting
Extra labour
Compatibility checks
Additional setup

Controllers can be useful, but they should be selected only where they suit the system and household.

Outdoor location cost factors

Instant gas systems are commonly installed outdoors, but location still matters.

Cost may increase if:

The existing location is non-compliant
Clearances are not suitable
The unit needs to be moved
Pipework needs rerouting
Wall mounting is difficult
Access is poor
The system is near windows, doors, boundaries or confined spaces
Weather protection or impact protection is required

Do not assume the existing location automatically suits the new unit.

Indoor instant gas replacement

Some older gas hot water systems may be indoors or flued.

Indoor gas installations have stricter requirements.

Before replacing an indoor system, check:

Model suitability
Flue requirements
Ventilation
Combustion air
Clearance requirements
Gas safety requirements
Drainage
Compliance
Access

A licensed gas fitter should confirm the correct replacement pathway.

Pipework changes

Pipework changes can affect replacement cost.

Extra work may include:

Moving hot and cold water lines
Adjusting gas connection position
Rerouting pipework
Replacing old fittings
Correcting non-compliant pipework
Installing or replacing valves
Adding insulation where required
Modifying pipe routes after relocation

A unit that looks similar may still have different connection positions.

Old unit removal and disposal

Old unit removal and disposal may or may not be included depending on the selected option.

Cost may increase if:

The old unit is difficult to access
The old unit is heavy or awkward
The system is in a tight side path
Extra labour is needed
Disposal is not included
The old unit is attached to old or corroded pipework
The system is being changed from storage to instant gas

Check whether removal and disposal are included before ordering.

Instant gas brand and model cost differences

Brand and model can affect product price, flow rate, warranty terms, features, dimensions and installation requirements.

Installed Today’s homepage-linked hot water brands worth comparing include:

Compare by gas type, flow rate, household demand and installation requirements, not brand name alone.

Rinnai instant gas replacement cost factors

Rinnai Hot Water Systems are commonly compared for instant gas hot water.

Rinnai may suit:

Continuous flow gas replacement
Compact outdoor hot water
16L, 20L or 26L comparisons depending on model range
Homes already using gas
Customers wanting a recognised gas appliance brand
Two-bathroom homes where gas supply supports the unit

Cost may depend on flow rate, gas type, gas pipe sizing, water pressure, controller requirements, access and old unit removal.

Rheem instant gas replacement cost factors

Rheem Hot Water Systems are often compared by customers wanting a major hot water brand across gas storage, instant gas, electric and heat pump options.

Rheem may suit:

Instant gas replacement
Gas storage vs instant gas comparison
Customers comparing multiple hot water types
Homes with suitable gas and water supply
Customers wanting a recognised hot water brand

Check gas type, flow rate, dimensions, warranty terms and installation requirements before ordering.

Bosch instant gas replacement cost factors

Bosch Hot Water Systems are often compared for gas hot water and continuous flow systems.

Bosch may suit:

Gas hot water replacement
Compact instant gas comparisons
Homes with suitable gas supply
Customers comparing natural gas and LPG options where available
Properties where model compatibility is confirmed

Before choosing Bosch, confirm gas type, flow rate, ignition requirements, water pressure and installation suitability.

Instant gas vs electric storage replacement cost

Instant gas and electric storage suit different homes.

Instant gas may suit:

Homes already using natural gas or LPG
Customers wanting compact wall-mounted hot water
Homes replacing continuous flow gas
Properties with suitable gas pipe sizing
Homes with suitable water pressure

Electric storage may suit:

Homes without gas
Units and townhouses
Simple electric replacement jobs
Properties with suitable electrical supply
Customers wanting stored hot water

Compare Electric Hot Water Systems if gas installation would be too complex or the property does not have gas.

Instant gas vs heat pump replacement cost

Instant gas and heat pump hot water have very different installation requirements.

Instant gas may suit:

Homes already connected to natural gas or LPG
Customers wanting compact continuous flow hot water
Properties with suitable gas pipe sizing
Homes where a storage tank is not preferred
Customers replacing existing instant gas

Heat pump hot water may suit:

Homes replacing electric storage
Homes with rooftop solar
Customers wanting efficient electric hot water
Properties with suitable outdoor airflow
Properties with suitable condensate drainage
Customers moving away from gas

Compare Heat Pump Hot Water Systems if long-term efficient electric hot water is the goal and the property suits heat pump installation.

What may be included in instant gas replacement?

Inclusions vary by product, selected option and installation pathway.

Possible inclusions may include:

Instant gas hot water unit
Standard connection to existing pipework
Basic labour where an installed option is selected
Standard commissioning
Standard valves where included
Old unit removal where included
Disposal where included

Do not assume every job includes gas pipework upgrades, electrical work, controllers, relocation, drainage, removal, disposal or compliance upgrades.

Check the selected product and service details carefully.

What may not be included?

Extra costs may include:

Gas pipework upgrades
New power point
Controller supply and installation
Water pipework changes
Gas connection changes
Valve replacement
Old unit removal
Disposal
Wall mounting changes
Relocation
Difficult access
Compliance upgrades
LPG-specific setup
Indoor flue work
Additional materials

This is why two homes replacing the same instant gas unit can have different total costs.

Maintenance costs after replacement

Instant gas hot water systems need maintenance to support safe and reliable operation.

Maintenance may include:

Gas safety checks
Burner inspection
Heat exchanger checks
Water filter checks where applicable
Error code checks
Controller checks
Leak inspections
Flue and clearance checks where relevant
Water pressure checks
General system inspection

Maintenance requirements depend on the model, water quality, usage and manufacturer instructions.

Signs your instant gas system needs replacing

Replacement may be worth considering if the unit is:

Showing frequent error codes
Failing to ignite
Producing fluctuating water temperature
Struggling with demand
Requiring repeated repairs
Very old
Leaking
Corroded
Not compatible with current household demand
No longer compliant
Costly to repair
Wrong gas type for the property

If repairs are becoming frequent, replacement may be the better long-term decision.

Repair vs replacement cost

Repair may make sense if:

The unit is relatively new
The issue is minor
Parts are available
Warranty may apply
The gas supply and water pressure are suitable
The unit is still correctly sized
The installation is otherwise compliant

Replacement may make sense if:

The unit is old
Repairs are frequent
Parts are difficult to get
The unit is undersized
Household demand has changed
Gas pipework upgrades are needed anyway
The installation is no longer compliant
You want to change flow rate or system type

A licensed gas fitter can help determine whether repair or replacement is the better option.

Rebates and incentives

Some hot water systems may be eligible for rebates, certificates or incentives depending on product, location, installer, scheme rules and installation pathway.

However, rebate rules can change.

Before relying on any rebate, check:

Current eligibility
Product eligibility
Installer requirements
State or territory rules
Documentation requirements
Whether the price includes the incentive
Whether the incentive is applied upfront or claimed later
Whether the old system type affects eligibility

Do not choose a system only because of a rebate. It still needs to suit the home.

Supply-only instant gas hot water systems

Supply-only ordering can suit customers who already have their own licensed gas fitter or plumber arranged.

Supply only may suit:

Builders
Renovators
Landlords
Property managers
Trade customers
Homeowners managing their own installation
Customers outside supplied-and-installed service areas

Supply-only product pricing generally does not include installation, valves, old unit removal, disposal, gas work, pipework changes, electrical work, controller wiring, drainage, access upgrades or compliance upgrades unless clearly selected or included.

Before ordering supply only, your licensed installer should confirm the instant gas hot water system suits the property.

Supplied-and-installed instant gas hot water systems

Supplied-and-installed options may be available on selected products in eligible Brisbane and Gold Coast service areas where shown.

This can suit customers who want the product and installation pathway arranged together.

Before ordering supplied and installed, check:

Service area eligibility
Existing system type
Installation inclusions
Natural gas or LPG
Gas pipe sizing
Water pressure
Electrical work where relevant
Controller requirements
Valve requirements
Old unit removal
Disposal
Pipework changes
Access
Compliance upgrades
Product suitability

Do not assume every possible site requirement is included. Check the selected product and installation options carefully.

How to reduce instant gas replacement surprises

Before ordering, collect:

Photos of the existing unit
Existing model number
Existing flow rate
Gas type
Photos of gas pipework
Photos of water pipework
Photos of power point or electrical supply
Installation location photos
Access photos
Number of bathrooms
Number of people in the home
Whether two showers run at once
Whether the old unit struggled
Whether controllers are needed
Whether you want supply only or installed where available

Better information makes it easier to choose the right unit and avoid surprises.

Common mistake: choosing by flow rate only

A larger L/min rating is not always better.

The home must have suitable gas supply and water pressure to support the unit.

Common mistake: choosing the wrong gas type

Natural gas and LPG are different.

Always confirm the correct gas type before ordering any gas hot water system.

Common mistake: ignoring gas pipe sizing

Instant gas units often need more gas supply than older systems.

If the gas pipework is undersized, the system may not perform properly.

Common mistake: ignoring water pressure

Instant gas systems need suitable water pressure and flow.

Poor pressure should be diagnosed before choosing a replacement.

Common mistake: assuming storage-to-instant is a simple swap

Changing from gas storage to instant gas may need gas pipework, electrical power, wall mounting, pipework changes and compliance checks.

Common mistake: assuming instant gas means instant hot water at the tap

Instant gas means the unit heats water on demand. It does not mean hot water reaches every tap instantly.

Pipe length still affects wait time.

Common mistake: comparing only the product price

The product price is not the total replacement cost.

Gas pipework, electrical work, controllers, pipework changes, removal, disposal and compliance work can all affect the final cost.

Common mistake: DIY instant gas installation

Instant gas hot water installation must be completed by a licensed gas fitter or suitable licensed professional.

DIY gas work can create:

Gas leaks
Carbon monoxide risk
Fire risk
Water leaks
Scalding risks
Warranty problems
Insurance issues
Non-compliant work
Poor performance
Serious safety hazards

Use the right licensed professional.

Final verdict: how much should you budget for instant gas hot water replacement?

Instant gas hot water replacement cost depends on the unit, gas type, flow rate, gas pipe sizing, water pressure, electrical requirements, controllers, pipework changes, old unit removal, disposal, access and compliance requirements.

A like-for-like instant gas replacement can be relatively straightforward where the existing setup is suitable.

Changing from gas storage, electric storage or heat pump hot water to instant gas can involve more work and should be assessed carefully.

Start by comparing Instant Gas Hot Water Systems, Gas Hot Water Systems, Hot Water Systems, Electric Hot Water Systems and Heat Pump Hot Water Systems.

The best replacement is not always the largest flow rate or cheapest product. It is the instant gas system that matches your gas type, water pressure, household demand, installation location and total replacement budget.

Long-tail FAQs

How much does it cost to replace an instant gas hot water system?

Instant gas replacement cost depends on brand, flow rate, gas type, gas pipe sizing, water pressure, electrical requirements, controller options, access, old unit removal, disposal and compliance needs.

Is instant gas cheaper to replace than gas storage?

It depends on the existing setup. Like-for-like instant gas replacement can be straightforward, but changing from gas storage to instant gas may require extra gas, electrical and pipework changes.

What size instant gas hot water system do I need?

The right size depends on bathrooms, shower use, whether multiple outlets run at once, water pressure, gas pipe sizing and household demand. Common sizes include 16L, 20L and 26L classes.

Is 26L instant gas worth it?

A 26L instant gas unit can suit many higher-demand or two-bathroom homes, but only where gas supply and water pressure support it.

Can I replace gas storage with instant gas?

Yes, where the property is suitable. Gas pipe sizing, water pressure, electrical power, wall mounting, pipework and compliance requirements need to be checked.

Can I replace electric hot water with instant gas?

Yes, but it can be more complex if the home does not already have suitable gas supply. Compare heat pump hot water as another electric upgrade option.