Instantaneous Hot Water Systems: Australian Buyer’s Guide for Continuous Flow Hot Water

Instantaneous hot water systems heat water as it is needed, instead of storing hot water in a tank. They are often called instant hot water systems, tankless hot water systems or continuous flow hot water systems.

For many Australian homes, the most common whole-home instantaneous option is a continuous flow gas hot water system. These systems are compact, wall-mounted and designed to heat water while a hot tap or shower is running. Electric instantaneous systems also exist, but whole-home electric instantaneous hot water can require significant electrical capacity, so it is not always a simple replacement for a standard electric storage unit.

The best instantaneous hot water system depends on your gas type, flow rate needs, number of bathrooms, household size, water pressure, installation location and whether you are replacing like-for-like or changing from a storage tank.

Installed Today supplies a range of instant gas hot water systems, along with broader hot water systems, electric hot water systems and heat pump hot water systems for customers comparing replacement options.

Quick answer: what is an instantaneous hot water system?

An instantaneous hot water system heats water on demand. When a hot tap or shower is turned on, water flows through the unit and is heated before it reaches the outlet.

Unlike a storage hot water system, it does not keep a full tank of hot water heated all day. This can save space and reduce standby heat loss, but the system must be correctly sized for the property’s flow rate and hot water demand.

In practical terms:

• Instantaneous gas hot water is usually the main whole-home option for homes with natural gas or LPG

• Instantaneous electric hot water may suit selected point-of-use or site-specific applications

• Electric storage or heat pump hot water may be better for homes without gas

• Flow rate matters because the system must keep up with showers, taps and simultaneous use

Is instantaneous hot water the same as continuous flow?

Yes. In most Australian hot water searches, “instantaneous hot water”, “instant hot water”, “tankless hot water” and “continuous flow hot water” are used to describe systems that heat water as it passes through the unit.

For gas systems, the most common term is continuous flow gas hot water system.

For electric systems, you may see terms like instant electric hot water or electric instantaneous hot water, but these need careful checking because the electrical requirements can be higher than many standard homes are set up for.

How instantaneous hot water systems work

An instantaneous hot water system activates when water begins flowing through the unit.

In a gas continuous flow system:

1. You turn on a hot tap or shower

2. The system detects water flow

3. The gas burner ignites

4. Water passes through a heat exchanger

5. Heated water flows to the outlet

6. The unit stops heating when the hot tap is turned off

In an electric instantaneous system:

1. You turn on a hot tap

2. Water flows through the unit

3. Electric elements heat the water as it passes through

4. Heated water travels to the outlet

The system does not store a full tank of hot water. It heats only when there is demand.

Does instantaneous mean hot water comes out immediately?

Not always.

Instantaneous means the unit heats water when needed, not that hot water appears at the tap instantly.

You may still wait for hot water depending on:

• Distance between the unit and the outlet

• Pipe length

• Pipe diameter

• Whether hot water has recently been used

• Flow rate from the tap or shower

• The home’s plumbing layout

If the instantaneous unit is far from the bathroom, there can still be a delay while cooled water in the pipework clears.

Main benefits of instantaneous hot water systems

Instantaneous hot water can be a strong choice when the property suits it.

Compact design

Continuous flow gas systems are usually smaller than storage tanks and mounted externally on a wall. This can help in homes with limited ground space, narrow side paths, townhouses, units, duplexes and properties where a large tank is awkward.

On-demand heating

The system heats water only while a hot outlet is running. It does not keep a tank of water hot between uses.

No stored hot water running out

A correctly sized continuous flow system can keep heating water while the tap is running. This can be useful for households that dislike running out of stored hot water.

However, it still has a maximum flow rate. It is not unlimited if too many outlets are used at the same time.

Good like-for-like replacement option

If your home already has an external gas continuous flow unit, replacing it with a similar natural gas or LPG model may be a practical pathway.

Like-for-like replacement is usually simpler than changing system type, but the gas type, flow rate, valves, water pressure and compliance requirements still need to be checked.

Instantaneous gas hot water systems

Instantaneous gas hot water systems are the most common whole-home instantaneous systems used in Australian homes.

They are available in different flow rates, usually measured in litres per minute.

Common sizes include:

• 16 L/min

• 20 L/min

• 26 L/min

A 16 L/min system may suit a smaller one-bathroom home. A 20 L/min system may suit moderate demand. A 26 L/min system is commonly compared for family homes and two-bathroom properties.

You can compare current options in the instant gas hot water systems collection.

Natural gas vs LPG instantaneous hot water

Gas hot water systems must match the property’s fuel type.

Natural gas and LPG are not interchangeable. A natural gas model cannot simply be used on LPG, and an LPG model cannot simply be used on natural gas unless the manufacturer provides an approved conversion pathway handled by a licensed gas fitter.

Before ordering, check:

• Whether the property uses natural gas or LPG

• The gas type shown on the existing unit label

• Whether the new model matches the gas type

• Whether the home has a gas meter or LPG bottles

• Whether the gas supply is suitable for the selected unit

• Whether a licensed gas fitter has confirmed the replacement

This is especially important for acreage homes, granny flats, rentals, duplexes and properties where LPG bottles are used.

What size instantaneous gas hot water system do you need?

Instantaneous gas systems are sized by flow rate, not tank capacity.

As a general guide:

Flow rate should match the way the home is used. A small home may not need the largest unit. A family home may be frustrated by a system that is too small.

Why flow rate is so important

Flow rate affects how much hot water the system can deliver at once.

If one shower is running, a smaller unit may be fine. If two showers, a kitchen tap and laundry demand are running together, the system needs to support a much higher load.

Flow rate performance depends on:

• Number of bathrooms

• Number of people in the home

• Shower head flow rate

• Whether outlets run at the same time

• Incoming water temperature

• Desired outlet temperature

• Water pressure

• Gas pipe sizing

• Gas meter or LPG supply

• Distance from unit to outlets

Do not choose instantaneous hot water only by price. Choose it by suitability.

Instantaneous electric hot water systems

Instantaneous electric hot water systems heat water using electric elements as water flows through the unit.

They can be useful for some point-of-use applications, but whole-home electric instantaneous systems can require significant electrical capacity. This may involve electrical checks or upgrades, depending on the property and selected unit.

Instantaneous electric may suit:

• Small point-of-use applications

• Selected hand basins

• Small studios or specific fixtures

• Properties where the electrical setup supports the unit

• Situations confirmed by a licensed electrician and plumber

For many homes without gas, electric storage hot water or heat pump hot water may be a more practical whole-home comparison.

Instantaneous hot water vs electric storage

Electric storage hot water systems keep heated water in a tank. Instantaneous systems heat water only while it is flowing.

If your current system is electric storage and the home has no gas, changing to instantaneous gas may involve more work than staying electric or comparing heat pump hot water.

Instantaneous hot water vs heat pump hot water

Instantaneous gas and heat pump hot water are very different systems.

Instantaneous gas heats water as it flows. Heat pump hot water stores hot water in a tank but uses heat from the surrounding air to help heat the water more efficiently than standard electric storage in suitable conditions.

If the property already has gas continuous flow, replacing with another instantaneous gas model may be practical. If the home has solar power and outdoor space, heat pump hot water may also be worth comparing.

Is instantaneous hot water good for a 1 bathroom home?

Instantaneous gas hot water can suit a 1 bathroom home, especially where the property already has natural gas or LPG.

A 16 L/min unit may suit:

• 1–2 people

• One shower

• Small homes

• Granny flats

• Units or townhouses

• Moderate hot water use

If the home has longer showers, future rental use or higher demand, a 20 L/min system may be worth comparing.

Is instantaneous hot water good for a 2 bathroom home?

Instantaneous gas hot water can suit a 2 bathroom home if the system is correctly sized and the gas supply is suitable.

A 26 L/min unit is commonly compared for:

• Family homes

• Two bathrooms

• 3–5 people

• Back-to-back showers

• Higher daily hot water demand

The key question is whether two showers may run at the same time. If simultaneous use is common, your licensed installer should confirm gas pipe sizing, water pressure and system suitability before ordering.

Is instantaneous hot water good for apartments and units?

Instantaneous gas hot water may suit apartments and units that already have a suitable gas setup.

However, apartment replacements can be more complex because of:

• Body corporate rules

• External wall access

• Flue requirements

• Balcony clearances

• Internal vs external unit location

• Shared services

• Gas type

• Access for trades

• Limited installation space

External gas continuous flow units are outdoor appliances unless the model is specifically approved for internal/flued installation. Do not assume an outdoor gas unit can be installed indoors, in a cupboard or in an enclosed area.

For many apartments, a small electric storage replacement may be the more practical option.

Is instantaneous hot water good for townhouses and duplexes?

Instantaneous gas hot water can be a strong option for townhouses and duplexes with suitable gas supply and external wall space.

It may suit:

• Narrow side paths

• Limited ground space

• Existing wall-mounted gas replacements

• One or two bathroom homes

• Properties already using natural gas or LPG

• Homes where a storage tank is awkward

Townhouses and duplexes may also have body corporate rules, tight access or shared boundaries, so clearances and approvals may need to be checked.

Is instantaneous hot water good for rental properties?

Instantaneous gas hot water can suit rental properties where the existing setup is already gas and the unit is correctly sized.

For rentals, the system should be:

• Reliable

• Easy for tenants to use

• Correctly sized for likely occupancy

• Matched to natural gas or LPG

• Installed in a compliant external location

• Practical to maintain

• Suitable for future tenants, not only the current household

Avoid undersizing a rental property just to reduce product cost. A 16 L/min unit may suit a small rental, but a family rental may need a 20 L/min or 26 L/min system depending on bathrooms and usage.

Is instantaneous hot water good for Airbnb and short-stay properties?

Instantaneous gas hot water can suit Airbnb and short-stay properties if the system is sized for maximum guest occupancy.

Short-stay guests may use hot water differently from permanent residents. They may shower back-to-back, use two bathrooms, run baths, or use laundry between bookings.

For short-stay properties, consider:

• Maximum guest count

• Number of bathrooms

• Whether two showers may run together

• Bath use

• Guest expectations

• LPG bottle management if applicable

• Simple operation

• Fast recovery between guest use

A system that suits two owner-occupiers may not suit a short-stay listing that sleeps six people.

Can you replace a storage tank with instantaneous hot water?

You may be able to replace a storage hot water system with an instantaneous system, but it is not always a simple swap.

Changing from storage to instantaneous gas may involve:

• Gas supply checks

• Gas pipe sizing checks

• Electrical connection for the gas unit

• Water pipework changes

• Wall mounting

• Valve upgrades

• Drainage changes

• Outdoor clearance checks

• Compliance upgrades

• Old tank removal

• Disposal where arranged

Changing from gas storage to instant gas may be more practical than changing from electric storage to gas, because the property may already have gas. Even then, gas pipe sizing and installation requirements still need to be checked.

Can you replace electric storage with instantaneous gas?

Yes, in some homes, but it can involve extra work.

If the property does not already have gas, changing from electric storage to instantaneous gas may require:

• Gas connection

• Gas pipework

• External wall location

• Electrical connection

• Pipework changes

• Valve changes

• Old tank removal

• Compliance upgrades

In homes without gas, electric storage or heat pump hot water may be a simpler and more cost-effective replacement path.

Installation considerations for instantaneous hot water

Instantaneous hot water systems must be installed correctly for safe and reliable operation.

Important checks may include:

• Natural gas or LPG type

• Gas pipe sizing

• Gas meter or LPG bottle capacity

• Water pressure

• Required flow rate

• Electrical connection

• External wall location

• Clearances from openings

• Drainage

• Valve requirements

• Access for servicing

• Controller wiring if selected

• Existing pipework condition

• Compliance with current requirements

Gas systems must be installed by a licensed gas fitter. Electrical work must be completed by a licensed electrician where required.

Why location matters

The location of an instantaneous hot water unit affects performance, installation cost and convenience.

A good location should consider:

• Distance to bathrooms and kitchen

• External clearances

• Gas supply route

• Electrical access

• Water pipework

• Service access

• Weather exposure

• Neighbouring windows or doors

• Boundary clearances

• Drainage

• Noise from operation

Installing the unit closer to major hot water outlets may reduce wait time, but it must still meet clearance and compliance requirements.

What does instantaneous hot water cost?

The cost depends on the product, flow rate, brand, gas type and installation requirements.

Key cost factors include:

• 16 L/min vs 20 L/min vs 26 L/min

• Natural gas vs LPG

• Brand and model

• Supply-only or supplied-and-installed

• Like-for-like replacement or system change

• Gas pipework

• Electrical connection

• Valve requirements

• Pipework changes

• Old unit removal

• Disposal

• Access issues

• Compliance upgrades

For the most accurate product comparison, check the current instant gas hot water systems range and confirm installation requirements with your licensed installer.

Supply only vs supplied and installed

Installed Today offers supply-only ordering across major Australian metro areas for customers who already have their own licensed installer arranged. Supplied-and-installed options are available on selected products in eligible Brisbane and Gold Coast service areas where shown.

Supply-only pricing generally does not include installation, valves, gas work, electrical work, pipework changes, drainage changes, old unit removal, disposal or compliance upgrades unless those items are clearly shown or selected.

Before ordering supply only, confirm with your licensed installer that the selected system suits:

• The gas type

• Flow rate

• Current location

• Household demand

• Gas supply

• Water pressure

• Electrical requirements

• Site access

Instantaneous hot water in Brisbane and Gold Coast

For eligible Brisbane and Gold Coast service areas, Installed Today offers supplied-and-installed options on selected hot water products where available.

Common instantaneous gas options include:

• 16 L/min continuous flow gas systems

• 20 L/min continuous flow gas systems

• 26 L/min continuous flow gas systems

• Natural gas models

• LPG models

• Selected Rinnai, Rheem and other brand options

Check the product page carefully for installation availability, current pricing, inclusions and any add-ons that may apply.

Instantaneous hot water supply-only for other metro areas

Installed Today also supports supply-only ordering across major Australian metro areas for customers who already have their own licensed local installer arranged.

This can suit customers outside eligible supplied-and-installed areas who want to order a suitable product online and arrange local installation separately.

Before ordering, confirm:

• Delivery availability

• Correct gas type

• Correct flow rate

• Installer approval

• Installation location

• Access

• Any local requirements

• Whether old unit removal is handled separately

Maintenance for instantaneous hot water systems

Instantaneous hot water systems still require maintenance.

Depending on the model, water quality and site conditions, maintenance may include:

• Cleaning inlet filters

• Checking gas burner operation

• Checking error codes

• Inspecting controllers

• Checking water pressure

• Inspecting valves

• Flushing or descaling where required

• Checking for leaks

• Servicing in line with manufacturer instructions

Poor water quality, hard water, sediment and scale can affect performance. If your home has sediment, chlorine taste, tank water or appliance scaling, a separate water filter system may also be worth comparing.

Common issue: temperature fluctuation

Temperature fluctuation can happen if the system is undersized, flow changes suddenly, water pressure is poor or multiple outlets are used at once.

Possible causes include:

• Low water pressure

• Blocked filters

• Undersized system

• Gas supply issue

• Poor pipe sizing

• High simultaneous demand

• Faulty components

• Shower mixer issues

• Tempering valve issues

A licensed professional should diagnose recurring temperature problems.

Common issue: system does not activate

An instantaneous system may not activate if there is not enough flow through the unit.

This may be caused by:

• Low-flow tapware

• Blocked inlet filter

• Low water pressure

• Closed or partially closed valve

• Flow sensor issue

• Gas supply issue

• Electrical issue

• Unit fault

Do not open or repair the unit yourself. Have it checked by a qualified technician.

Common issue: not enough hot water at two outlets

A continuous flow system has a maximum capacity. If the home uses more hot water than the system can deliver, performance may drop.

For example, a smaller unit may handle one shower but struggle when two showers and a kitchen tap run together.

This may be a sizing issue, gas supply issue, water pressure issue or plumbing layout issue.

Common mistake: thinking instantaneous means unlimited

Instantaneous hot water systems can keep heating while water flows, but they still have limits.

They are limited by:

• Flow rate

• Gas supply

• Water pressure

• Incoming water temperature

• Pipe sizing

• Simultaneous use

• Unit capacity

A correctly sized system can perform well. An undersized system can disappoint.

Common mistake: choosing the wrong gas type

Natural gas and LPG models are different. Ordering the wrong model can delay installation and create extra cost.

Always confirm gas type before ordering.

Common mistake: choosing by price only

A cheaper instantaneous unit may be too small for the home or may not suit the gas supply.

Compare:

• Flow rate

• Gas type

• Brand

• Warranty terms

• Household demand

• Installation requirements

• Access

• Valves and extras

• Supply-only vs installed inclusions

The best-value system is the one that fits the home properly.

Common mistake: changing from storage to instant without checking extras

Changing from a storage tank to instantaneous hot water can require additional work.

Check gas, electrical, pipework, wall mounting, valves, drainage, clearances and compliance before ordering.

Common mistake: expecting no wait time at the tap

Instantaneous systems heat on demand, but pipe length still matters.

If the system is far from the bathroom, water in the pipe must clear before hot water reaches the tap.

Final recommendation

Instantaneous hot water systems can be an excellent option for homes with suitable natural gas or LPG, especially where space is limited and a compact continuous flow system makes sense.

For smaller homes, a 16 L/min system may be enough. For moderate use, 20 L/min may be worth comparing. For family homes and many two-bathroom properties, 26 L/min is commonly compared, provided the gas supply and water pressure are suitable.

If your home does not have gas, compare whether electric storage hot water or heat pump hot water is a better replacement pathway.

The best instantaneous hot water system is not just the biggest or cheapest model. It is the system that matches your gas type, flow rate, household demand, installation location and budget.

To compare options, browse instant gas hot water systems or view the full Installed Today hot water systems range.

Long-tail FAQs

What is an instantaneous hot water system?

An instantaneous hot water system heats water as it is used instead of storing hot water in a tank. It is also called instant hot water, tankless hot water or continuous flow hot water.

Is instantaneous hot water actually instant?

The unit heats water as soon as flow is detected, but hot water still needs to travel through the pipework to the tap. If the unit is far from the bathroom, there may still be a short wait.

What size instantaneous gas hot water system do I need?

A small one-bathroom home may compare 16 L/min, moderate homes may compare 20 L/min, and two-bathroom family homes often compare 26 L/min. The right size depends on gas supply, water pressure and simultaneous use.

Is instantaneous gas hot water good for families?

Instantaneous gas hot water can suit families when the system is correctly sized and the gas supply is suitable. Many family homes compare 26 L/min models, but the property must support the selected unit.

Is instantaneous electric hot water good for a whole house?

Instantaneous electric hot water can suit some applications, but whole-home systems may require significant electrical capacity. Many homes without gas may find electric storage or heat pump hot water more practical.

Can I replace my storage tank with instantaneous hot water?

Yes, in some homes. However, changing from storage to instantaneous may involve gas pipework, electrical connection, wall mounting, valves, drainage and compliance checks.

Does instantaneous hot water save space?

Yes. Continuous flow gas systems are usually compact and wall-mounted, which can save space compared with a storage tank.

Does instantaneous hot water run out?

A continuous flow system does not run out of stored hot water because it heats while water flows. However, it can still be overloaded if too many outlets run at once or if the unit is undersized.

Is natural gas the same as LPG for instantaneous hot water?

No. Natural gas and LPG systems are different. The selected model must match the property’s fuel type.

Does supply-only instantaneous hot water include installation?

No. Supply-only generally means the product is supplied only. Installation, valves, gas work, electrical work, pipework changes, drainage, old unit removal, disposal and compliance upgrades are separate unless clearly shown as included.