Continuous Hot Water Systems: Instant Gas vs Instant Electric Buying Guide

Oct 5, 2024

A continuous hot water system heats water only when you turn on a hot tap. Instead of storing hot water in a tank, it heats water as it flows through the unit. This can give your home continuous flow hot water, save space and reduce standby heat loss compared with some storage systems.

For most whole-home applications, instant gas hot water systems are the main continuous hot water option to compare. Instant electric hot water systems can suit small point-of-use applications, but they are not always suitable for whole-home shower demand because electrical requirements can be high.

Installed Today makes it easy to compare and order hot water systems online, with supply-only ordering available across major Australian metro areas and selected supplied-and-installed options available on eligible products in Brisbane and Gold Coast service areas.

Quick Answer: What Is a Continuous Hot Water System?

A continuous hot water system, also called a continuous flow hot water system, heats water on demand instead of storing it in a tank.

As a general guide:

Instant gas hot water is the most common continuous flow option for whole-home use
26L instant gas systems are often compared for larger households and higher shower demand
20L instant gas systems may suit smaller-to-medium households
16L instant gas systems may suit lower-demand homes or smaller applications
Instant electric hot water is usually better suited to small point-of-use needs
Natural gas and LPG units are not interchangeable
Gas pipe sizing and water pressure must support the selected unit

Before ordering supply only, confirm the correct model, flow rate, gas type, water pressure, gas pipe sizing, electrical requirements, access and installation location with your licensed installer.

How Continuous Hot Water Systems Work

A continuous hot water system heats water as it passes through the unit.

When you turn on a hot tap:

Cold water flows into the system
The unit detects water flow
A gas burner or electric element activates
Water is heated as it passes through the heat exchanger or heating element
Hot water flows to the tap
The unit stops heating when the tap is turned off

This means the system does not need to keep a large tank of water hot all day.

For whole-home hot water, continuous flow usually means an instant gas unit. For smaller sinks, offices or compact applications, instant electric may also be considered.

Continuous Gas Hot Water Systems

A continuous gas hot water system uses natural gas or LPG to heat water on demand. These systems are commonly wall-mounted outside and are available in different flow rates, commonly 16L, 20L and 26L.

A continuous gas hot water system may suit homes that:

Want hot water on demand
Want to avoid a large storage tank
Already have suitable natural gas or LPG
Have enough water pressure
Have suitable gas pipe sizing
Have an outdoor wall location
Want a compact replacement option

You can compare Installed Today’s instant gas hot water systems or browse 26L instant gas hot water systems for larger household options.

Gas work must be completed by a licensed gas fitter.

Continuous Electric Hot Water Systems

A continuous electric hot water system heats water using electric heating elements as water flows through the unit.

These systems may suit:

Small sinks
Offices
Compact kitchens
Granny flats
Low-demand fixtures
Point-of-use hot water
Space-limited applications

They are not always suitable for whole-home hot water because the electrical demand can be significant. A licensed electrician or installer should confirm whether the property can support the selected unit before ordering.

For compact options, compare instant electric hot water systems.

Continuous Flow vs Storage Hot Water

Continuous flow systems and storage systems both provide hot water, but they work differently.

System Type	How It Works	Best Suited To
Instant gas hot water	Heats water as it passes through the unit	Whole-home continuous flow hot water where gas supply and water pressure suit
Instant electric hot water	Heats water on demand using electric elements	Small point-of-use applications
Electric storage hot water	Heats and stores water in a tank	Simple replacements and homes without gas
Gas storage hot water	Heats and stores water using gas	Homes already set up for natural gas or LPG
Heat pump hot water	Uses heat from surrounding air to heat stored water	Energy-focused homes with suitable outdoor space

If you want a familiar tank-style replacement, compare electric hot water systems or gas hot water systems.

If running cost and energy efficiency are important, compare heat pump hot water systems as well.

Benefits of a Continuous Hot Water System

Hot Water on Demand

A continuous hot water system heats water when needed. This avoids storing a full tank of hot water and can provide continuous flow hot water when the system is correctly sized and supported by the property.

Compact Design

Instant gas systems are usually compact and wall-mounted. This can free up space compared with a large storage tank.

No Large Storage Tank

Because there is no large tank constantly storing hot water, continuous flow systems can reduce standby heat loss compared with some storage systems.

Good Option for Gas-Connected Homes

If the home already has suitable natural gas or LPG, a continuous gas hot water system can be a practical replacement option.

Multiple Size Options

Instant gas systems are available in different flow rates, so homes can compare 16L, 20L and 26L models depending on household demand and site suitability.

Limitations of Continuous Hot Water Systems

Continuous hot water systems are not perfect for every home.

Potential limitations include:

Gas pipe sizing must be checked
Water pressure must support the system
Natural gas and LPG models must be selected correctly
External gas units must not be installed indoors unless specifically approved as internal flued models
Long pipe runs can still cause a delay at distant taps
Instant electric units may need significant electrical capacity
Larger units may involve extra installation requirements
Temperature controllers may be optional depending on the model

A licensed installer should confirm site suitability before ordering.

Natural Gas vs LPG Continuous Hot Water

Natural gas and LPG continuous hot water systems are different. They are not interchangeable.

Natural gas is supplied through a gas network connection
LPG is supplied from gas bottles or cylinders
A natural gas unit must not be connected to LPG unless approved by the manufacturer and converted by a licensed gas fitter
An LPG unit must not be connected to natural gas unless approved by the manufacturer and converted by a licensed gas fitter

Installed Today stocks separate natural gas and LPG options, including:

Always order the correct gas type.

What Size Continuous Hot Water System Do You Need?

Continuous gas hot water systems are commonly compared by litres per minute. The most common sizes are 16L, 20L and 26L.

The right size depends on:

Number of people in the home
Number of bathrooms
Shower habits
Whether multiple showers run at once
Kitchen and laundry hot water use
Incoming water temperature
Gas pipe sizing
Water pressure
Distance from the unit to fixtures
Natural gas or LPG availability

Bigger is not always better. A larger system will not perform properly if the property does not have enough gas supply or water pressure.

16L Continuous Gas Hot Water Systems

A 16L continuous gas hot water system may suit smaller homes or lower-demand applications.

It may be considered for:

Smaller households
One-bathroom homes
Lower shower demand
Replacing an existing 16L unit
Compact applications where demand is modest

Relevant options include:

20L Continuous Gas Hot Water Systems

A 20L continuous gas hot water system may suit small-to-medium households with moderate hot water demand.

It may suit:

Smaller families
Moderate shower use
One-to-two bathroom homes, depending on fixtures and habits
Replacing an existing 20L unit
Homes where a 26L unit is not required or not supported by the site

Relevant options include:

26L Continuous Gas Hot Water Systems

A 26L instant gas hot water system is often compared for larger households or higher hot water demand.

It may suit:

Family homes
Homes with higher shower demand
Two-bathroom homes, depending on usage
Larger households
Replacing an older continuous flow unit
Homes where gas supply and water pressure support the system

Relevant options include:

For 26L systems, gas pipe sizing and water pressure are especially important. A licensed gas fitter should confirm suitability before ordering.

Continuous Gas vs Gas Storage Hot Water

Gas hot water systems include both continuous gas and gas storage options.

Continuous gas systems heat water as it flows through the unit. Gas storage systems heat and store water in a tank.

Continuous gas may suit homes that:

Want a compact wall-mounted unit
Want to avoid a large tank
Have suitable gas supply and water pressure
Want continuous flow hot water
Have a suitable outdoor wall location

Gas storage may suit homes that:

Prefer stored hot water
Already have a gas storage system
Want a familiar replacement type
Have suitable outdoor space for a tank
Have usage patterns that suit storage hot water

Common gas storage categories include 130/135L gas hot water systems, 160/170L gas hot water systems and 5-star gas hot water systems.

Continuous Hot Water vs Heat Pump Hot Water

A continuous gas system and a heat pump system solve hot water needs in different ways.

A continuous gas system heats water as it is used. A heat pump stores hot water in a tank but uses heat from the surrounding air to help heat the water efficiently.

A heat pump hot water system may be worth comparing if:

You want to reduce electricity use compared with standard electric storage
You have suitable outdoor space
The area has good airflow
Condensate drainage can be managed
Noise placement is suitable
You want to pair hot water heating with rooftop solar where timing and usage suit

Many homes compare medium heat pump hot water systems 200L–280L, while larger households may compare large heat pump hot water systems.

Installation Requirements for Continuous Gas Hot Water

Before buying a continuous gas hot water system, your licensed installer should check:

Natural gas or LPG supply
Correct gas type
Gas pipe sizing
Water pressure
Water flow rate
Outdoor installation location
Required clearances
Ventilation and flue requirements where applicable
Electrical requirements for ignition or controls
Pipework route
Access for future servicing
Existing valves and compliance requirements

Gas work must be completed by a licensed gas fitter.

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

Installation Requirements for Continuous Electric Hot Water

Before buying an instant electric system, your installer or electrician should check:

Electrical supply capacity
Circuit requirements
Switchboard capacity
Cable sizing
Water pressure
Flow rate
Intended use
Distance to the fixture
Compliance requirements
Whether the unit suits point-of-use or whole-home demand

Instant electric systems can be useful, but they should not be treated as a simple whole-home replacement without checking electrical requirements.

What Is Not Included in Supply-Only Pricing?

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

It does not usually include:

Installation labour
New valves
Electrical work
Gas work
Pipework changes
Drainage changes
Tempering valve upgrades
Pressure limiting valve upgrades
Expansion control valves
Old unit removal
Disposal
Compliance upgrades
Concrete bases or slab work
Relocation of the system

Always check the product page and confirm the full installation requirements with your licensed installer before ordering.

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.

Supply-only may suit you if:

Your installer has confirmed the correct model
The correct gas type has been selected
Gas pipe sizing has been checked
Water pressure has been checked
Electrical requirements are understood
Access and installation location are suitable
You understand what is not included in the product price

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

Brisbane and Gold Coast Considerations

For Brisbane and Gold Coast homes, continuous gas hot water can be a practical option where the property has suitable natural gas or LPG, outdoor wall space and water pressure.

Common local considerations include:

Natural gas vs LPG availability
Older gas pipework
Gas pipe sizing for 26L systems
Water pressure
Outdoor unit location
Side access
Distance to bathrooms
Existing valve condition
Whether the old unit was gas storage or continuous flow
Whether electric storage or heat pump may be a better fit

Installed Today offers supply-only ordering across major Australian metro areas, with selected supplied-and-installed options available on eligible products in Brisbane and Gold Coast service areas.

Brand Options to Compare

Installed Today stocks a range of major hot water brands, including:

For continuous gas hot water, Rinnai, Rheem and Bosch are commonly compared across different sizes and gas types. Brand matters, but the correct size, gas type, water pressure and installation suitability matter more.

Common Mistakes When Choosing a Continuous Hot Water System

Choosing a 26L Unit Without Checking Gas Pipe Sizing

A 26L system can suit some family homes, but only if the gas supply supports it.

Ordering the Wrong Gas Type

Natural gas and LPG units are different. Always select the correct model.

Assuming Instant Electric Can Run the Whole Home

Instant electric systems can require significant electrical capacity and are often better suited to point-of-use applications.

Ignoring Water Pressure

Continuous flow systems need suitable water pressure and flow to perform properly.

Expecting Instant Hot Water at Every Tap Immediately

Continuous flow means the unit heats water on demand. There may still be a delay while hot water travels through pipework to the tap.

Installing an External Gas Unit Indoors

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

Assuming Supply-Only Includes Installation

Supply-only generally means product only unless installation is selected or clearly shown.

Before Ordering Checklist

Before ordering a continuous hot water system, confirm:

Whether you need gas or electric
Whether the property has natural gas or LPG
Correct gas type
Required flow rate
Number of bathrooms
Number of people in the home
Peak shower demand
Gas pipe sizing
Water pressure
Electrical requirements
Outdoor installation location
Clearances and access
Whether temperature controllers are required
Whether new valves may be needed
Whether drainage or pipework changes are needed
Whether storage or heat pump hot water may suit better
Installer confirmation before buying supply only

Frequently Asked Questions

What is a continuous hot water system?

A continuous hot water system heats water as it flows through the unit. It does not store a full tank of hot water. It is also called a continuous flow, instantaneous or tankless hot water system.

Is continuous hot water the same as instant hot water?

In most cases, yes. Continuous hot water, instant hot water and continuous flow hot water usually refer to systems that heat water on demand.

Is continuous gas hot water good for families?

Continuous gas hot water can suit families where the system is correctly sized and the property has suitable gas supply and water pressure. Many larger households compare 26L systems.

What size continuous hot water system do I need?

The right size depends on household size, bathrooms, shower habits, gas supply and water pressure. Common gas sizes include 16L, 20L and 26L.

Is 26L continuous gas hot water enough for a family?

A 26L unit can suit some family homes, but only where gas pipe sizing and water pressure support it. A licensed gas fitter should confirm suitability.

Can I use LPG with a natural gas continuous hot water system?

No. Natural gas and LPG systems are not interchangeable unless the manufacturer allows an approved conversion by a licensed gas fitter. Always order the correct gas type.

Does continuous hot water mean no waiting?

Not exactly. The system heats water on demand, but there may still be a short delay while hot water travels through the pipework to the tap.

Can an external continuous gas unit be installed indoors?

No. External gas units are designed for outdoor installation unless the specific model is approved for internal flued installation.

Is instant electric hot water suitable for a whole home?

Not always. Instant electric systems can require significant electrical capacity and are often better suited to point-of-use applications.

Can I install a continuous hot water system myself?

No. Continuous hot water systems involve plumbing, gas, electrical work, water pressure, valves and compliance requirements. Use licensed trades.

What is not included in supply-only pricing?

Supply-only pricing generally excludes installation, valves, electrical work, gas work, pipework changes, drainage, old unit removal, disposal and compliance upgrades unless selected or clearly shown.

Final Word

A continuous hot water system can be a strong option for homes that want hot water on demand, a compact unit and no large storage tank. For whole-home use, continuous gas hot water is usually the main option to compare, especially in 16L, 20L and 26L sizes.

The right system depends on more than flow rate. Gas type, gas pipe sizing, water pressure, household demand, installation location and electrical requirements all matter.

Before ordering supply only, get your licensed installer to confirm the correct model, gas type, flow rate and site requirements. That way, your continuous hot water system is matched properly to the home before it arrives.

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