Instant Water Heating Systems: Gas vs Electric and What to Compare Before You Buy

An instant water heating system heats water only when a hot tap is turned on. Instead of storing hot water in a tank, the system heats water as it flows through the unit. This can make instant hot water a compact and practical option for the right home or fixture.

Instant water heating can mean different things depending on the system. Instant gas hot water is commonly used for whole-home hot water where natural gas or LPG is available. Instant electric hot water is often better suited to point-of-use applications such as hand basins, kitchenettes, small offices, workshops and low-demand sinks.

The best instant water heating system depends on household size, number of bathrooms, shower habits, gas type, gas pipe sizing, water pressure, electrical supply, installation location and whether you need whole-home hot water or a smaller point-of-use solution.

Installed Today helps customers compare instant gas hot water systems, 26L instant gas hot water systems, instant electric hot water systems and broader 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

Choose an instant gas hot water system if you want compact continuous flow hot water for a home with suitable natural gas or LPG, correct gas pipe sizing, suitable water pressure and an outdoor installation location.

Choose an instant electric hot water system if you need hot water for a small point-of-use application such as a sink, kitchenette, office, workshop or low-demand fixture, and the electrical supply is suitable.

Instant systems can provide continuous hot water within the unit’s rated capacity, but they are not unlimited in every situation. Multiple showers, high-flow fixtures or simultaneous hot water use can still exceed the system’s capacity.

For larger homes, compare 20L and 26L instant gas systems carefully. For sinks and small fixtures, compare instant electric systems, but do not assume instant electric is suitable for whole-home shower use without checking electrical requirements.

What Is an Instant Water Heating System?

An instant water heating system heats water as it is needed.

When a hot tap opens, water flows through the unit. A flow sensor activates the heater, and either a gas burner or electric element heats the water before it reaches the outlet.

Instant systems are different from storage hot water systems because they do not keep a tank of hot water ready all day.

Instant water heating systems are often described as:

• Instant hot water systems

• Continuous flow hot water systems

• Tankless hot water systems

• Instant gas hot water systems

• Instant electric hot water systems

• On-demand hot water systems

The right product depends on whether you want whole-home hot water or point-of-use hot water.

How Instant Water Heating Works

The basic process is:

• A hot tap is turned on

• The system detects water flow

• A gas burner or electric element activates

• Water passes through the heat exchanger or heating chamber

• Heated water travels to the tap, shower or fixture

• The unit turns off when water flow stops

The performance depends on flow rate, temperature rise, incoming water temperature, pressure, gas supply or electrical capacity.

Instant Gas Hot Water Systems

An instant gas hot water system uses natural gas or LPG to heat water on demand.

Instant gas is commonly used for whole-home hot water, especially where the home already has gas and the installation location is suitable.

Instant gas may suit:

• Homes with natural gas or LPG

• Households wanting compact wall-mounted hot water

• Like-for-like replacement of an existing continuous flow unit

• Properties with suitable gas pipe sizing

• Homes with suitable water pressure

• Customers wanting hot water heated on demand

• Outdoor installation locations with correct clearances

Common instant gas sizes include 16L, 20L and 26L systems.

Instant Electric Hot Water Systems

An instant electric hot water system uses electricity to heat water as it flows through the unit.

Instant electric is often best suited to smaller point-of-use applications rather than full household hot water.

Instant electric may suit:

• Hand basins

• Small sinks

• Kitchenettes

• Offices

• Workshops

• Low-demand fixtures

• Areas where a storage tank is not practical

• Short pipe runs to a single outlet

Instant electric may not suit:

• Whole-home shower demand without a suitable electrical setup

• Multiple bathrooms

• High-flow fixtures

• Homes with limited electrical capacity

• Installations where dedicated circuits or three-phase power are not available

Some instant electric units can have significant electrical requirements. Electrical suitability should be checked before ordering, and electrical work must be completed by a licensed electrician where required.

Instant Gas vs Instant Electric

Instant gas and instant electric are both “instant” systems, but they suit different applications.

Instant Gas May Suit:

• Whole-home hot water

• Multiple fixture use within capacity

• Homes with natural gas or LPG

• Outdoor wall-mounted installation

• Replacing an existing gas continuous flow unit

• Larger hot water demand where gas pipe sizing and pressure are suitable

Instant Electric May Suit:

• Point-of-use hot water

• Small sinks

• Offices

• Workshops

• Kitchenettes

• Hand basins

• Low-demand fixtures

• Compact spaces where storage is not practical

Key Difference

Instant gas is usually the more common option for whole-home continuous flow hot water.

Instant electric is usually better treated as a point-of-use solution unless the property has the electrical capacity and installation design to support larger demand.

Does Instant Hot Water Mean Endless Hot Water?

Instant systems can provide continuous hot water while water is flowing, but only within the unit’s rated capacity.

A continuous flow system can still be overloaded if too many fixtures are used at once.

For example, performance may be affected by:

• Two showers running at once

• A shower and kitchen tap running together

• High-flow showerheads

• Low water pressure

• Undersized gas pipework

• Incorrect LPG or natural gas model

• Long pipe runs

• Cold incoming water

• Electrical supply limitations for instant electric systems

A 26L instant gas system may suit some larger households, but gas pipe sizing and water pressure must be suitable. Bigger is not automatically better.

Best Instant Gas Hot Water Systems to Compare

There is no single best instant water heating system for every home. The right option depends on gas type, flow rate, household demand and installation requirements.

Rinnai Infinity B26 Natural Gas Hot Water System

The Rinnai Infinity B26 Natural Gas Hot Water System may suit households comparing a 26L natural gas continuous flow option.

It may suit:

• Medium to larger households

• Homes with natural gas

• Properties with suitable gas pipe sizing

• Homes with suitable water pressure

• Customers wanting a compact outdoor wall-mounted system

• Like-for-like replacement of an existing 26L natural gas unit

For 26L systems, gas pipe sizing and water pressure must be checked before ordering.

Rinnai Infinity B26 LPG Gas Hot Water System

The Rinnai Infinity B26 LPG Gas Hot Water System may suit homes that use LPG bottles and need a higher-capacity continuous flow option.

It may suit:

• LPG properties

• Rural or acreage homes where LPG is already used

• Higher hot water demand

• Outdoor wall-mounted installation

• Customers comparing 26L LPG systems

LPG bottle setup, regulator suitability, gas pipe sizing and water pressure should be confirmed by a licensed gas fitter before purchase.

Rheem 26L Natural Gas Hot Water System

The Rheem 26L Natural Gas Hot Water System is another option for homes comparing 26L natural gas continuous flow systems.

It may suit:

• Natural gas homes

• Larger households where demand suits a 26L system

• Properties with suitable gas pipework

• Homes with suitable water pressure

• Customers comparing Rheem instant gas products

A 26L system can still be exceeded if multiple fixtures run at once. Sizing should be based on real hot water use.

Rheem 26L LPG Gas Hot Water System

The Rheem 26L LPG Gas Hot Water System may suit LPG homes where higher hot water demand and installation conditions support a 26L system.

It may suit:

• Homes using LPG bottles

• Medium to larger households

• Outdoor wall-mounted installation

• Customers wanting an LPG continuous flow option

• Properties where gas supply and water pressure have been checked

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

Rheem 20L Natural Gas Hot Water System

The Rheem 20L Natural Gas Hot Water System may suit small to medium households with moderate hot water demand.

It may suit:

• Homes with natural gas

• Moderate shower use

• Smaller to medium households

• Like-for-like 20L replacements

• Customers who may not need a 26L system

A 20L unit may be more suitable than a 26L system where demand is lower or gas supply does not support a larger unit.

Rheem 20L LPG Gas Hot Water System

The Rheem 20L LPG Gas Hot Water System may suit LPG homes with moderate hot water demand.

It may suit:

• Smaller LPG homes

• Moderate hot water use

• Outdoor installation

• Like-for-like replacement

• Customers comparing mid-size LPG continuous flow options

Gas bottle setup and regulator suitability should still be checked.

Rinnai Infinity B16 Natural Gas Hot Water System

The Rinnai Infinity B16 Natural Gas Hot Water System may suit smaller households or lower-demand natural gas applications.

It may suit:

• Small homes

• Single bathroom homes

• Granny flats

• Lower simultaneous hot water use

• Like-for-like replacement of a smaller instant gas unit

A 16L unit may not suit homes where multiple showers or fixtures are used at the same time.

Rinnai Infinity B16 LPG Gas Hot Water System

The Rinnai Infinity B16 LPG Gas Hot Water System may suit lower-demand LPG applications.

It may suit:

• Small LPG homes

• Granny flats

• Single bathroom setups

• Lower water demand

• Customers comparing compact LPG continuous flow options

As with all gas systems, the LPG setup, regulator and pipework should be checked before ordering.

Instant Electric Hot Water Options

Instant electric hot water is often chosen for small, specific outlets.

It may be useful where you need hot water close to the point of use and do not want a storage tank.

Customers can compare instant electric hot water systems, along with broader electric hot water systems.

Instant electric may be a good fit for:

• Hand basins

• Compact kitchens

• Office sinks

• Workshops

• Utility sinks

• Point-of-use hot water

• Short pipe runs

Before choosing instant electric, check electrical supply, circuit requirements, flow rate and the temperature rise needed.

Instant Water Heating vs Storage Hot Water

Instant systems and storage systems solve different problems.

Instant Systems

Instant systems heat water as needed.

They may suit:

• Compact wall-mounted installation

• Homes wanting on-demand hot water

• Point-of-use applications

• Gas homes with suitable supply

• Smaller spaces where a tank is not ideal

Storage Systems

Storage systems heat and store water in a tank.

They may suit:

• Homes wanting a familiar tank-style system

• Electric storage replacements

• Gas storage replacements

• Larger stored hot water capacity

• Properties where instant gas pipe sizing or electrical supply is not suitable

Customers comparing storage alternatives can browse electric hot water systems, including 250L electric hot water systems, 315L electric hot water systems and 400L electric hot water systems.

Instant Water Heating vs Heat Pump Hot Water

A heat pump hot water system is usually a larger storage-style system that uses electricity to move heat from the surrounding air into the water tank.

A heat pump hot water system may suit homes wanting an efficient electric storage-style option where outdoor space, airflow, drainage and electrical supply are suitable.

Instant Hot Water May Suit:

• Compact installation

• Gas homes with suitable supply

• Point-of-use applications

• Homes wanting hot water heated on demand

• Like-for-like instant replacement

Heat Pump May Suit:

• Homes replacing older electric storage

• Properties without gas

• Customers wanting an efficient electric storage-style system

• Homes with outdoor space

• Locations with clear airflow

• Properties where condensate drainage can be managed

• Homes with solar PV where timer operation suits usage

Customers comparing heat pump alternatives can browse medium heat pump hot water systems from 200L to 280L and large heat pump hot water systems over 280L.

What Size Instant Gas Hot Water System Do You Need?

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

Consider:

• Number of people in the home

• Number of bathrooms

• Shower length

• Whether showers run at the same time

• Bath use

• Kitchen and laundry use

• Showerhead flow rates

• Existing system performance

• Natural gas or LPG

• Gas pipe sizing

• Water pressure

• Distance from unit to outlets

16L Instant Gas

A 16L instant gas system may suit small homes, single bathroom properties, granny flats or lower-demand households.

20L Instant Gas

A 20L instant gas system may suit small to medium homes with moderate demand.

26L Instant Gas

A 26L instant gas system may suit higher-demand households, but only where gas pipe sizing and water pressure are suitable.

A 26L system is not automatically best for every home. Multiple outlets can still exceed capacity.

Installation Requirements for Instant Gas Hot Water

Instant gas installation can involve plumbing, gas fitting and sometimes electrical work.

A licensed gas fitter should confirm:

• Natural gas or LPG type

• Gas pipe sizing

• Gas meter or LPG bottle setup

• Regulator suitability for LPG

• Appliance gas load

• Location and clearances

• Ventilation requirements

• Water pressure

• Temperature control requirements

• Compliance requirements

Gas work must be completed by a licensed gas fitter.

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

Installation Requirements for Instant Electric Hot Water

Instant electric installation can involve plumbing and electrical work.

A licensed electrician may need to check:

• Circuit capacity

• Switchboard capacity

• Phase requirements

• Cable size

• Protection devices

• Isolation requirements

• Whether the system can support the required flow and temperature rise

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

Instant electric should not be chosen for whole-home shower demand without confirming electrical suitability first.

Running Costs and Energy Use

Instant water heating systems can reduce standby heat loss because they do not store a tank of heated water. However, running costs still depend on the home and energy source.

Running costs can be affected by:

• Hot water usage

• Shower length

• Number of occupants

• Gas price

• LPG bottle costs

• Electricity tariff

• System size

• Flow rate

• Temperature setting

• Incoming water temperature

• Maintenance condition

• Whether the system is correctly sized

Do not choose an instant system based only on a generic savings claim. Compare the system against the home’s actual usage and energy source.

Rebates, STCs and Incentives

Rebates and incentives can change and do not apply to every hot water system.

Some efficient hot water systems, especially selected heat pump or solar products, may be eligible for STCs, rebates or incentives depending on product type, location, installation details and current program rules.

Instant gas and instant electric systems are not automatically eligible for rebates.

Before choosing a system based on incentives, confirm current eligibility and whether any discount is already included in the advertised price.

Maintenance for Instant Water Heating Systems

Maintenance needs depend on system type, water quality, usage and manufacturer instructions.

Maintenance may include:

• Cleaning inlet filters

• Checking for error codes

• Checking hot water temperature stability

• Inspecting valves

• Checking gas ignition where applicable

• Servicing gas components where required

• Checking electrical connections where required

• Descaling where hard water affects performance

• Following manufacturer guidance

If the unit has low flow, temperature fluctuation or frequent errors, the issue may involve water pressure, gas supply, scale, filters, sensors, valves or installation conditions.

Installed Today is positioned as an online supplier of hot water systems, water filters and pumps, with selected supplied-and-installed options on eligible products in Brisbane and Gold Coast service areas where shown. General repair diagnosis, emergency plumbing and ongoing servicing should be handled by licensed trades where required.

Brisbane and Gold Coast Considerations

In Brisbane and Gold Coast homes, instant water heating system choice can be affected by:

• Natural gas availability

• LPG bottle setup

• Water pressure

• Gas pipe sizing

• Narrow side access

• Outdoor wall location

• Eaves, windows and clearances

• Existing valve condition

• Electrical supply

• Switchboard capacity

• Apartment or body corporate rules

• Coastal exposure on the Gold Coast

• Whether the old system kept up with demand

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

• LPG bottle supply

• LPG regulator upgrades

• Relocation of the system

• Rebate administration

• Site assessment

For instant gas systems, confirm gas type, gas pipe sizing, water pressure, clearances and outdoor location with a licensed gas fitter.

For instant electric systems, confirm circuit requirements, electrical capacity, flow rate and fixture suitability with a licensed electrician where required.

Common Instant Water Heating Mistakes

Assuming Instant Means Unlimited

Instant systems have rated capacities. Multiple fixtures can still exceed output.

Choosing 26L Gas Without Checking Pipe Sizing

A 26L system may need more gas supply than the existing pipework can provide.

Ordering the Wrong Gas Type

Natural gas and LPG are different. The selected model must match the property’s gas type.

Using Instant Electric for Whole-Home Demand Without Checking Electrical Supply

Instant electric can require high electrical capacity and may not suit whole-home shower use.

Installing an External Gas Unit Indoors

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

Ignoring Water Pressure

Both instant gas and instant electric systems need suitable flow and pressure to perform correctly.

Assuming Supply-Only Includes Installation

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

Before Ordering Checklist

Before choosing an instant water heating system, check:

• Do you need whole-home hot water or point-of-use hot water?

• Is the home natural gas, LPG or electricity only?

• Does the selected model match the gas type?

• Is gas pipe sizing suitable?

• Is LPG regulator setup suitable?

• Is water pressure suitable?

• How many bathrooms are used daily?

• Are showers used at the same time?

• Does the household use a bath?

• Is the system for a sink, kitchenette or shower?

• Is electrical supply suitable for instant electric?

• Is three-phase power required?

• Is outdoor gas unit placement suitable?

• Are clearances suitable?

• Is a temperature controller required?

• Is a tempering valve required?

• 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

What is an instant water heating system?

An instant water heating system heats water only when a hot tap is turned on. It does not store hot water in a tank.

Is instant hot water the same as continuous flow?

In many cases, yes. Continuous flow usually refers to an instant system that heats water as it flows through the unit. Instant gas systems are common continuous flow hot water systems.

Is instant gas better than instant electric?

Instant gas is usually more suitable for whole-home hot water where gas supply, pipe sizing and water pressure are suitable. Instant electric is usually better for point-of-use applications such as sinks, kitchenettes and offices.

Can instant hot water run out?

An instant system does not run out like a storage tank, but it can be overloaded if hot water demand exceeds the unit’s capacity.

What size instant gas 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.

Is 26L instant gas suitable for every home?

No. A 26L system may suit some larger homes, but gas pipe sizing and water pressure must be suitable. Bigger is not automatically better.

Is instant electric suitable for a shower?

Some instant electric systems may support shower use in specific applications, but electrical requirements can be significant. Many instant electric systems are better suited to low-demand fixtures. Electrical suitability should be confirmed before ordering.

Can I install an instant water heater myself?

No. Instant water heater installation can involve plumbing, gas fitting and electrical work. Licensed trades should complete the work where required.

Does supply-only pricing include installation?

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

Final Word

An instant water heating system can be a compact and practical option when matched correctly to the home or fixture.

Instant gas hot water can suit whole-home continuous flow demand where natural gas or LPG, gas pipe sizing, water pressure and outdoor installation location are suitable. Instant electric hot water can suit point-of-use fixtures such as sinks, kitchenettes, offices and workshops where electrical supply is suitable.

The best system depends on hot water demand, energy source, pressure, pipework, electrical capacity and installation conditions.

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

For supply-only orders, confirm gas type, gas pipe sizing, water pressure, electrical requirements and installation suitability with licensed trades before purchasing.