Instantaneous Gas Hot Water Installation Regulations: What to Know Before Ordering

Installing an instantaneous gas hot water system is not a DIY job. It involves gas fitting, plumbing, temperature control, water pressure checks, ventilation clearances and compliance documentation. The system must be selected correctly, installed by licensed trades where required and matched to the property’s gas type, gas pipe sizing and water pressure.

An instantaneous gas hot water system, also called continuous flow gas hot water, heats water only when a hot tap is turned on. It can be a compact and efficient option for homes with natural gas or LPG, but the installation requirements are more involved than simply mounting a unit on the wall.

Installed Today helps customers compare instant gas hot water systems, 26L instant gas hot water systems and broader gas hot water systems online. Supply-only ordering is available across major Australian metro areas, with selected supplied-and-installed options available on eligible products in Brisbane and Gold Coast service areas where shown.

Quick Answer

Instantaneous gas hot water installation must be completed by licensed trades where required. Gas work must be completed by a licensed gas fitter, and plumbing work should be completed by a licensed plumber where required.

Before ordering an instant gas hot water system, check:

• Natural gas or LPG supply

• Correct gas type for the unit

• Gas pipe sizing

• Water pressure

• Household hot water demand

• Number of bathrooms

• Outdoor wall location

• Ventilation and clearance requirements

• Whether the model is external or internal flued

• Temperature control requirements

• Electrical ignition or power requirements

• Access for installation and future servicing

• Compliance certificate requirements

• Whether the product is supply-only or supplied-and-installed

For larger models, such as 26L instant gas hot water systems, gas pipe sizing and water pressure are especially important. Bigger is not automatically better, and multiple outlets can still exceed the system’s capacity.

What Is an Instantaneous Gas Hot Water System?

An instantaneous gas hot water system heats water as it flows through the unit. When a hot tap is opened, the system detects water flow, ignites the gas burner and heats water on demand.

Unlike gas storage hot water, an instantaneous system does not store a tank of hot water.

Instant gas hot water may suit:

• Homes with natural gas or LPG

• Properties with suitable gas pipe sizing

• Homes with suitable water pressure

• Customers wanting continuous flow hot water

• Homes with limited ground space

• Outdoor wall-mounted locations

• Like-for-like replacement of an existing instant gas unit

Common sizes include 16L, 20L and 26L units. Customers often compare products such as the Rinnai Infinity B16 Natural Gas Hot Water System, Rheem 20L Natural Gas Hot Water System, Rinnai Infinity B26 Natural Gas Hot Water System and Rheem 26L Natural Gas Hot Water System.

Instantaneous Gas vs Gas Storage Hot Water

Instantaneous gas and gas storage systems both use gas, but they work differently.

Instantaneous Gas Hot Water

Instantaneous gas systems heat water on demand.

They may suit:

• Homes wanting a compact wall-mounted system

• Properties with limited ground space

• Households wanting continuous flow hot water

• Existing instant gas replacements

• Homes with suitable gas pipe sizing and water pressure

Gas Storage Hot Water

Gas storage systems heat and store water in a tank.

They may suit:

• Like-for-like gas storage replacements

• Homes that already have a suitable gas storage location

• Customers wanting a familiar tank-style system

• Properties where instant gas pipe sizing is not suitable

• Homes with natural gas or LPG already connected

Customers comparing tank-style options can browse 130/135L gas hot water systems and 160/170L gas hot water systems.

Who Can Install an Instantaneous Gas Hot Water System?

An instantaneous gas hot water system must be installed by licensed trades where required.

Gas work must be completed by a licensed gas fitter. This can include gas pipework, appliance connection, testing, commissioning and compliance documentation.

Plumbing work should be completed by a licensed plumber where required. This can include water pipework, valves, pressure control, drainage and temperature control devices.

Electrical work must be completed by a licensed electrician where required. Some instantaneous gas systems use electrical ignition or require a compliant power outlet or connection.

DIY installation is not suitable because incorrect installation can create serious risks, including:

• Gas leaks

• Fire risk

• Carbon monoxide risk

• Water temperature hazards

• Invalid product warranty

• Non-compliance

• Poor performance

• Damage to the appliance

• Insurance issues

For supply-only orders, confirm the model and installation requirements with your licensed installer before purchasing.

Main Regulations and Standards to Consider

Instantaneous gas hot water installation must follow current laws, standards, manufacturer instructions and local authority requirements. Requirements can vary by state, territory, property type and installation situation.

The installer may need to consider:

• Gas installation standards

• Plumbing and drainage standards

• Manufacturer installation manual

• National Construction Code requirements

• State or territory gas safety rules

• Local authority or network requirements

• Temperature control requirements

• Ventilation and clearance requirements

• Gas compliance certificate requirements

• Electrical safety requirements where applicable

For customers, the most important point is simple: choose the right unit first, then have the installation confirmed and completed by licensed trades.

Natural Gas vs LPG Requirements

Natural gas and LPG are not interchangeable.

A natural gas instantaneous hot water system must be connected to natural gas. An LPG instantaneous hot water system must be connected to LPG.

Ordering the wrong gas type can cause delays, safety issues and compliance problems.

Before ordering, confirm:

• Whether the property uses natural gas or LPG

• Whether the selected model matches the gas type

• Whether the gas supply is suitable

• Whether gas pipe sizing is suitable

• Whether the existing connection can support the new unit

• Whether the system is a like-for-like replacement or an upgrade

Product examples include:

• Rinnai Infinity B26 Natural Gas Hot Water System

• Rinnai Infinity B26 LPG Gas Hot Water System

• Rheem 26L Natural Gas Hot Water System

• Rheem 26L LPG Gas Hot Water System

Gas Pipe Sizing

Gas pipe sizing is one of the most important checks for instantaneous gas hot water systems.

Continuous flow gas units can require a strong and consistent gas supply. If the pipework is undersized, the system may not perform correctly. Temperature may fluctuate, the unit may fault, or other gas appliances may be affected.

Gas pipe sizing is especially important for 26L systems.

Before ordering a 26L unit, a licensed gas fitter should check:

• Existing gas pipe size

• Gas meter location

• Distance from gas meter to unit

• Other gas appliances on the property

• Natural gas or LPG supply

• Appliance gas load

• Whether upgrades are required

A larger instant gas unit is not automatically better. The property must be able to support it.

Water Pressure and Flow Requirements

Instantaneous gas systems need suitable water pressure and flow to operate correctly.

If water pressure is too low, too restricted or inconsistent, the system may not activate properly or may deliver unstable temperatures.

A licensed installer may need to check:

• Incoming water pressure

• Flow rate at fixtures

• Pipe sizing

• Pressure limiting valves

• Filters or strainers

• Tempering valves

• Fixture restrictions

• Distance from unit to outlets

• Simultaneous hot water use

Poor pressure should be diagnosed before choosing a larger unit. A new hot water system will not always fix pressure issues caused by pipework, valves or fixture restrictions.

Temperature Control Requirements

Hot water must be delivered safely to reduce scalding risk. New and replacement hot water systems may require a temperature control device, such as a tempering valve, depending on the installation and local requirements.

Temperature control matters for:

• Bathrooms

• Ensuites

• Showers

• Baths

• Basins used for personal hygiene

• Residential replacement installations

A tempering valve or suitable temperature control device helps blend hot and cold water so water delivered to personal hygiene fixtures is safer.

Temperature control devices should be installed in a practical, accessible location for servicing and replacement where required.

Outdoor vs Indoor Installation

Most domestic external instantaneous gas hot water systems are designed for outdoor installation.

An external gas hot water unit should not be installed indoors unless the model is specifically approved for internal flued installation and is installed with the correct flue system.

Before ordering, confirm whether the unit is:

• External only

• Internal flued

• Room-sealed

• Suitable for the proposed location

• Suitable for the required clearances

• Suitable for weather exposure

• Accessible for servicing

Do not assume an external gas hot water unit can be placed in a garage, cupboard, enclosed patio, roof space or internal room. The model and installation location must be checked by a licensed installer.

Ventilation and Clearance Requirements

Instantaneous gas hot water systems need correct ventilation and clearances for safe operation.

Clearance requirements can depend on:

• Manufacturer installation manual

• Gas standard requirements

• Whether the unit is external or internal flued

• Location of windows and doors

• Air vents and openings

• Eaves and ceilings

• Corners and walls

• Other appliances

• Electrical equipment

• Boundaries

• Service access

• Combustible materials

Generic clearance distances should not be relied on without checking the current appliance manual and installation rules. A licensed installer should confirm the proposed location before purchase, especially if the unit is near windows, doors, vents, eaves, fences or tight side access areas.

Electrical Requirements

Some instantaneous gas hot water systems require electricity for ignition, controls or temperature controllers.

Electrical requirements may include:

• A suitable weatherproof power outlet

• Correct location of the outlet

• Safe isolation

• Compliance with electrical rules

• Protection from weather

• Temperature controller wiring where applicable

Electrical work must be completed by a licensed electrician where required.

For supply-only orders, check whether the selected model needs power and whether the installation location has a suitable electrical setup.

Temperature Controllers

Some instantaneous gas systems can be paired with temperature controllers, depending on the model.

Temperature controllers may affect:

• User control

• Maximum temperature settings

• Bathroom temperature limits

• Kitchen temperature requirements

• Wiring requirements

• Installation cost

• Product compatibility

Temperature controllers are not always included with the base product. Check product inclusions before ordering.

Compliance Certificates and Documentation

Gas hot water installation may require compliance documentation from the licensed gas fitter or relevant installer.

This documentation helps show that the gas work has been completed and tested according to the required rules.

Customers should keep a copy of any compliance certificate, product warranty information and installation paperwork for future reference.

For Queensland properties, compliance processes and digital certificate requirements may apply. The licensed installer should complete the required documentation for the work performed.

Choosing the Right Instantaneous Gas Hot Water Size

The right size depends on the home’s hot water demand and the property’s gas and water supply.

Consider:

• Number of people in the home

• Number of bathrooms

• Shower length and frequency

• Whether showers run at the same time

• Bath use

• Kitchen and laundry use

• Existing system performance

• Distance from unit to outlets

• Gas pipe sizing

• Water pressure

• Natural gas or LPG availability

16L Instant Gas Systems

A 16L system may suit smaller households, lower demand, single bathroom homes or like-for-like replacements.

Options include the Rinnai Infinity B16 Natural Gas Hot Water System, Rinnai Infinity B16 LPG Gas Hot Water System and Rheem 16L Natural Gas Hot Water System.

20L Instant Gas Systems

A 20L system may suit small to medium households with moderate demand, depending on fixtures and usage.

Options include the Rheem 20L Natural Gas Hot Water System and Rheem 20L LPG Gas Hot Water System.

26L Instant Gas Systems

A 26L system may suit larger homes or higher hot water demand, but only if gas pipe sizing and water pressure are suitable.

Options include the Rinnai Infinity B26 Natural Gas Hot Water System, Rinnai Infinity B26 LPG Gas Hot Water System, Rheem 26L Natural Gas Hot Water System and Rheem 26L LPG Gas Hot Water System.

Bigger is not automatically better. Multiple outlets can still exceed the unit’s capacity if too many fixtures are used at once.

Like-for-Like Replacement vs System Change

A like-for-like instant gas replacement is usually simpler than changing system type, but it still needs licensed checks.

A system change may involve more work if you are:

• Switching from electric storage to instant gas

• Switching from gas storage to instant gas

• Relocating the unit

• Changing from natural gas to LPG

• Upgrading from a smaller instant gas unit to a 26L unit

• Adding temperature controllers

• Installing new valves

• Upgrading gas pipework

• Changing water pipework

• Adding electrical supply

• Correcting non-compliant work

A licensed installer should confirm the scope before the product is ordered.

Brisbane and Gold Coast Considerations

In Brisbane and Gold Coast homes, instantaneous gas hot water installation can be affected by property age, access, gas supply and location.

Common local considerations include:

• Narrow side access

• Older pipework

• Existing valve condition

• Natural gas meter location

• LPG bottle location

• Gas pipe sizing

• Water pressure

• Outdoor wall space

• Eaves, windows and door clearances

• Coastal exposure on the Gold Coast

• Whether the unit is replacing gas storage or electric storage

• Compliance upgrades

• Old unit removal

Selected supplied-and-installed options are available on eligible Installed Today products in Brisbane and Gold Coast service areas where shown. Availability depends on the product, address and installation requirements.

Supply-Only vs Supplied-and-Installed

Installed Today offers supply-only ordering across major Australian metro areas. This can suit customers who already have a licensed installer organised and want to order the product online.

Selected supplied-and-installed options are available on eligible products in Brisbane and Gold Coast service areas. Availability depends on the product, address and installation requirements.

For supply-only products, the listed product price generally covers the product only.

It does not usually include:

• Installation labour

• Plumbing alterations

• Electrical work

• Gas work

• New valves

• Pipework changes

• Gas pipe upgrades

• Drainage changes

• Tempering valve upgrades

• Pressure limiting valve upgrades

• Expansion control valves

• Old unit removal

• Disposal

• Compliance upgrades

• Concrete bases or slab work

• Flue kits unless listed

• Temperature controllers unless listed

• Relocation of the system

• Rebate administration

• Site assessment

For instantaneous gas systems, confirm gas type, gas pipe sizing, water pressure, ventilation clearances, electrical requirements and temperature control requirements with a licensed installer before ordering.

Common Mistakes to Avoid

Ordering the Wrong Gas Type

Natural gas and LPG models are different. Confirm the property’s gas type before ordering.

Choosing a 26L Unit Without Checking Pipe Sizing

A 26L unit may need more gas flow than the existing pipework can provide. Gas pipe sizing should be checked first.

Assuming External Units Can Go Indoors

External gas units are designed for outdoor installation unless the model is specifically approved for internal flued installation.

Ignoring Water Pressure

Instantaneous systems need suitable water flow and pressure. Poor water pressure can affect activation and temperature stability.

Not Checking Clearances

Windows, doors, vents, eaves, boundaries and other appliances can affect where the unit can be installed.

Forgetting Electrical Requirements

Some gas units require power for ignition, controls or temperature controllers.

Assuming Supply-Only Includes Installation

Supply-only pricing generally covers the product only unless installation is clearly selected or included.

Before Ordering Checklist

Before ordering an instantaneous gas hot water system, check:

• Is the home connected to natural gas or LPG?

• Does the selected model match the gas type?

• Is the existing unit instant gas, gas storage or electric?

• Is the replacement like-for-like or a system change?

• How many people live in the home?

• How many bathrooms are used daily?

• Are showers used at the same time?

• Does the household use a bath?

• Did the old system run out of hot water?

• Is gas pipe sizing suitable?

• Is water pressure suitable?

• Is the outdoor location suitable?

• Are ventilation and clearance requirements met?

• Is the unit external or internal flued?

• Is electrical power required?

• Are temperature controllers required?

• Is a tempering valve or temperature control device required?

• Are valves or pipework changes likely?

• Is old unit removal included or separate?

• Is the product supply-only or supplied-and-installed?

• Has a licensed installer confirmed suitability?

Frequently Asked Questions

Who can install an instantaneous gas hot water system?

Gas work must be completed by a licensed gas fitter. Plumbing work should be completed by a licensed plumber where required, and electrical work must be completed by a licensed electrician where required.

Can I install an instant gas hot water system myself?

No. Instantaneous gas hot water installation involves gas fitting, plumbing, safety checks and compliance requirements. DIY installation is not suitable.

Can an external gas hot water system be installed indoors?

No, not unless the model is specifically approved for internal flued installation and installed with the correct flue system. External gas hot water units are designed for outdoor installation.

What size instant gas hot water system do I need?

Common sizes include 16L, 20L and 26L. The right size depends on bathrooms, shower habits, simultaneous use, gas pipe sizing and water pressure. Bigger is not automatically better.

Is a 26L instantaneous gas system suitable for every home?

No. A 26L system can suit some larger homes, but the property must have suitable gas pipe sizing and water pressure. Multiple outlets can still exceed capacity.

Can I use an LPG unit on natural gas?

No. LPG and natural gas are not interchangeable. The unit must match the property’s gas type.

Do instant gas hot water systems need electricity?

Some models require electricity for ignition, controls or temperature controllers. Check the product specifications and confirm electrical requirements before ordering.

Do I need a tempering valve with an instant gas system?

A temperature control device may be required depending on the installation, fixtures and current rules. A licensed plumber should confirm what is required for the property.

Does supply-only pricing include installation?

No. Supply-only pricing generally covers the product only. It does not usually include gas fitting, plumbing labour, electrical work, valves, pipework changes, gas pipe upgrades, disposal or compliance upgrades unless clearly listed.

Final Word

Instantaneous gas hot water systems can be a practical option for homes with natural gas or LPG, but the installation must be handled carefully. Gas type, pipe sizing, water pressure, ventilation, clearances, temperature control and compliance documentation all matter.

Before ordering, confirm the selected model with a licensed installer. This is especially important for 26L systems, LPG properties, system relocations and upgrades from electric or gas storage.

Installed Today makes it easy to compare instant gas hot water systems, 26L instant gas hot water systems, gas hot water systems and broader hot water systems online.

For supply-only orders, confirm gas type, gas pipe sizing, water pressure, clearance requirements and installation suitability before purchasing. For eligible Brisbane and Gold Coast products, check whether a supplied-and-installed option is available where shown.