Instant Water Heating Systems: Are They Worth It for Australian Homes?

Instant water heating systems, also called instantaneous, tankless or continuous flow hot water systems, heat water only when a hot tap is turned on. Instead of storing hot water in a tank, they heat water as it passes through the unit.

For many Australian homes, an instant water heater can be a smart choice when space is limited, gas is available, or the household wants hot water on demand without a large storage cylinder. The most common whole-home instant systems are continuous flow gas hot water systems, while instant electric units are usually more site-specific and may need significant electrical capacity.

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

Quick answer: what is an instant water heating system?

An instant water heating system heats water as you use it. When a hot tap or shower is turned on, water flows through the unit and is heated before reaching the outlet.

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

For homes with natural gas or LPG, a continuous flow gas hot water system is often the main instant hot water option to compare. For homes without gas, electric storage, heat pump or suitable electric instantaneous options may need to be considered carefully.

What does “instant hot water” really mean?

“Instant hot water” can be a little misleading. The system heats water on demand, but hot water still has to travel from the unit to the tap or shower.

That means you may still wait a short time for hot water depending on:

• How far the unit is from the outlet

• The pipe length between the unit and bathroom

• The flow rate of the tap or shower

• Whether hot water has been used recently

• The home’s plumbing layout

An instant system does not mean hot water appears at every tap immediately. It means the unit does not rely on a stored tank of preheated water.

How instant water heaters work

An instant water heater activates when water starts flowing through the system.

In a gas continuous flow unit, the system detects flow, ignites the burner, and heats water through a heat exchanger as it passes through the unit. The heated water then travels through the pipework to the tap, shower or appliance being used.

In an electric instantaneous unit, water passes across electric heating elements. These systems can be compact, but whole-home electric instantaneous units can require high electrical load, so they are not always a simple replacement for a standard electric storage system.

For most Australian homes comparing whole-home instant hot water, gas continuous flow systems are usually the more common option.

Main benefits of instant water heating systems

Instant water heating systems can offer several practical benefits when the property is suitable.

They save space

Because there is no large storage tank, continuous flow systems are usually compact and wall-mounted. This can be useful for townhouses, units, small homes, tight side paths and properties where a large cylinder is difficult to place.

A gas continuous flow unit may free up ground space compared with a storage tank, but it still needs a compliant external location, correct clearances and suitable access.

They heat water on demand

Instant systems heat water when a hot outlet is opened. This means they are not constantly storing a large volume of hot water.

This can be useful for households that want a system designed around on-demand use rather than stored capacity.

They can suit continuous shower routines

A correctly sized continuous flow system can keep heating water while the tap is running, as long as gas supply, water pressure and system capacity are suitable.

This is one reason they are commonly compared for homes where people dislike running out of stored hot water. However, the unit still has a maximum flow rate, so sizing matters.

They can be compact for replacement jobs

If your home already has an external gas continuous flow system, replacing it with another suitable model can be a practical option. The property may already have the gas connection, water connections, external location and wall space required.

That does not mean every replacement is identical. Gas type, pipe sizing, valves, water pressure, electrical connection and compliance still need to be checked.

Instant gas vs instant electric hot water

The two main types of instant hot water are gas and electric, but they are not interchangeable.

If your home already has gas continuous flow hot water, replacing like-for-like is often the simplest instant option. If your home currently has electric storage and no gas, changing to instant gas may involve extra gas pipework and licensed trade work. If considering instant electric, the electrical requirements must be checked before ordering.

You can compare related alternatives in the hot water systems range, including electric hot water systems, instant gas hot water systems and heat pump hot water systems.

Gas instant hot water systems

Gas instant hot water systems are commonly called continuous flow gas hot water systems. They are available in different flow rates, often shown in litres per minute.

Common sizes include:

• 16 L/min

• 20 L/min

• 26 L/min

The right size depends on the number of bathrooms, number of people, expected simultaneous use, water pressure, incoming water temperature, gas supply and pipe sizing.

A 16 L/min system may suit smaller homes or one-bathroom properties. A 20 L/min system may suit moderate use. A 26 L/min system is commonly compared for two-bathroom homes and family use, but it still needs the right gas and water supply.

Natural gas vs LPG instant hot water

Gas instant systems must match the property’s fuel type.

Natural gas and LPG are not the same. A natural gas model cannot simply be used on LPG unless the manufacturer specifically provides a correct approved version or conversion path handled by a licensed gas fitter. In most online ordering situations, you should choose the correct model from the start.

Before ordering a gas continuous flow system, check:

• Whether the property uses natural gas or LPG

• The gas type shown on the existing unit

• Whether the new model matches that gas type

• Whether the system is external or internal/flued

• Whether the existing gas supply is suitable

• Whether the selected flow rate suits the home

• Whether a licensed gas fitter has confirmed requirements

This is especially important for homes using LPG bottles, acreage properties, granny flats and homes where the gas system has been altered over time.

What size instant hot water system do you need?

Instant hot water systems are usually selected by flow rate, not tank capacity.

As a general guide:

A larger number is not always automatically better. The unit must be supported by the property’s gas supply, pipe sizing and water pressure. If the existing gas line is undersized, simply buying a larger unit may not deliver the expected performance.

Why flow rate matters

Flow rate tells you how much hot water the system can produce under certain conditions.

A shower, kitchen tap and laundry tap all require flow. If multiple outlets are used at once, the demand increases. A system that is fine for one shower may struggle if two showers and a kitchen tap are used at the same time.

Real-world performance depends on:

• Incoming water temperature

• Desired outlet temperature

• Shower head flow rate

• Number of outlets running

• Gas supply

• Gas pipe sizing

• Water pressure

• Pipe length

• Unit capacity

This is why instant water heaters should be sized to the home, not chosen only by price.

Is instant hot water suitable for a 1 bathroom home?

Instant gas hot water can suit many 1 bathroom homes, especially where the property already has natural gas or LPG.

A 16 L/min system may be enough for a smaller household where one shower is used at a time. For higher-use homes, long showers or future flexibility, a 20 L/min model may be worth comparing.

For a 1 bathroom home without gas, electric storage or heat pump hot water may be more practical than trying to convert the property to gas.

Is instant hot water suitable for a 2 bathroom home?

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

A 26 L/min system is often compared for family homes, but the final choice depends on whether two showers may be used together, the gas pipe sizing, water pressure and household demand.

If the home has teenagers, a bath, high-flow shower heads or frequent simultaneous use, it is worth checking the setup carefully before ordering.

Is instant hot water suitable for apartments and units?

Instant gas hot water may suit apartments and units that already have suitable gas hot water infrastructure.

However, apartment replacements can be more restricted by:

• Body corporate rules

• Flue requirements

• External wall access

• Balcony clearances

• Shared services

• Gas type

• Building design

• Access for trades

• Existing internal or external unit location

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

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

Is instant hot water suitable for townhouses and duplexes?

Instant gas systems can be a good option for townhouses and duplexes where the property already has gas and suitable external wall space.

They may suit:

• Narrow side paths

• Limited ground space

• Existing wall-mounted gas replacements

• One or two bathroom homes

• Properties where a storage tank is awkward

• Homes with natural gas or LPG

The main checks are gas type, pipe sizing, water pressure, external clearances and body corporate requirements where applicable.

Can you replace a storage tank with instant hot water?

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

Changing from storage to instant may require:

• Gas supply checks

• Gas pipework upgrades

• Electrical connection for the gas unit

• Water pipework changes

• Wall mounting

• New valves

• Drainage checks

• Compliance upgrades

• Removal or disconnection of the old tank

• Confirmation of external clearances

If the property already has gas storage hot water, changing to instant gas may be more practical than changing from electric storage to gas. If the property has no gas at all, the cost and complexity may be higher.

Instant hot water vs electric storage

Electric storage hot water systems store heated water in a tank. Instant hot water systems heat water as needed.

If your home already has electric storage and no gas, staying with electric hot water or comparing heat pump hot water may be more practical than switching to gas.

Instant hot water vs heat pump hot water

Instant gas and heat pump hot water systems solve different problems.

Instant gas is compact and heats water as it flows. It can be a strong option where the home already has natural gas or LPG.

Heat pump hot water stores hot water in a tank but uses heat from the surrounding air to help heat the water. It may suit homes wanting a more efficient electric option with suitable outdoor space.

The right choice depends on the property, not just the system type.

Do instant water heaters save money?

Instant water heaters can reduce energy waste compared with storing hot water in a tank, especially where the system is correctly sized and used efficiently.

However, running costs depend on:

• Gas or electricity tariffs

• Household hot water use

• System efficiency

• Flow rate

• Pipe length

• Installation quality

• Gas type

• Climate

• Maintenance

• Whether the system is replacing a poor older unit

It is best to avoid assuming any fixed saving. A continuous flow gas system may be efficient for one home and less suitable for another depending on gas pricing, usage and installation requirements.

Installation considerations for instant hot water

Instant water heaters need to be installed correctly for safe, reliable operation.

Important checks may include:

• Correct gas type

• Gas pipe sizing

• Gas meter or LPG bottle setup

• Water pressure

• Flow rate requirements

• Electrical connection

• External wall location

• Clearances from windows, doors and openings

• Drainage

• Valve requirements

• Access for servicing

• Compliance with current requirements

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

Why existing location matters

Replacing an instant gas unit in the same location is usually simpler than moving the system or changing system type.

The existing location may already have:

• Gas connection

• Water connections

• External wall mounting

• Electrical point

• Suitable drainage

• Clearances

• Service access

Moving the unit can add complexity. It may require new gas pipework, water pipework, electrical work, wall mounting, drainage and compliance checks.

Common add-ons and extra work

Depending on the property and selected system, an instant hot water replacement may require:

• New isolation valves

• Tempering valve

• Pressure limiting valve

• Pipework alterations

• Gas pipe upgrades

• Electrical connection

• Controller wiring

• Drainage changes

• Wall brackets or mounting work

• Old unit removal

• Disposal

• Compliance upgrades

Supply-only product pricing usually does not include these items unless clearly selected or shown on the product page.

Maintenance for instant water heaters

Instant water heaters still need maintenance. They are not a set-and-forget product.

Maintenance needs may include:

• Checking filters

• Cleaning inlet strainers

• Inspecting burners on gas models

• Checking water pressure

• Checking temperature performance

• Inspecting controllers where fitted

• Flushing or descaling where water quality requires it

• Checking for leaks or corrosion

• Servicing in line with manufacturer guidance

Hard water, sediment and poor water quality can affect performance over time. If the home has noticeable sediment, chlorine taste, tank water or appliance scaling, water filtration may also be worth considering separately.

Why water pressure matters

Instant hot water systems rely on flow. If water pressure is poor, performance may be affected.

Low pressure can cause issues such as:

• Poor shower flow

• Temperature fluctuation

• Unit not activating correctly

• Reduced hot water comfort

• Problems when multiple outlets are used

Before adding a pump or changing systems, it is important to understand the cause of poor pressure. It may relate to incoming supply, pipework, valves, filters, shower heads, pressure limiting valves or the existing hot water system.

Common issue: temperature fluctuation

Temperature fluctuation can happen when flow changes, outlets are used together, or the system is not matched to the property.

Possible causes include:

• Low water pressure

• Blocked filters

• Incorrect gas supply

• Undersized system

• High simultaneous demand

• Poor pipe sizing

• Faulty components

• Shower mixers or tempering issues

• Scale or debris in the system

If an instant system is fluctuating, it should be checked by a licensed professional rather than adjusted randomly.

Common issue: system does not activate

An instant water heater may not activate if there is not enough water flow through the unit.

This can happen because of:

• Low flow tapware

• Blocked inlet filter

• Low water pressure

• Closed or partially closed valves

• Faulty flow sensor

• Gas or electrical issue

• Unit fault

• Incorrect installation conditions

If the system does not ignite or heat properly, it should be inspected by a qualified technician.

Common issue: not enough hot water at multiple outlets

Instant water heaters have a maximum flow capacity. If several outlets are used together, the demand may exceed what the unit can supply.

For example, a system may handle one shower well but struggle when two showers and a kitchen tap are used at the same time.

This does not always mean the unit is faulty. It may mean the system is undersized, the gas supply is limited, or the household is using more hot water than the system was designed for.

Should you upgrade to instant hot water?

Upgrading to instant hot water may be worth considering if:

• Your home already has gas

• You want a compact wall-mounted system

• You are replacing an old gas continuous flow unit

• You want hot water on demand

• You have limited space for a tank

• Your household demand suits the flow rate

• The gas supply and water pressure are suitable

It may not be the best choice if:

• Your home has no gas supply

• Electrical or gas upgrades would be expensive

• You need very high simultaneous flow

• The property has no suitable external location

• You live in an apartment with restrictions

• A heat pump or electric storage system suits the home better

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.

For instant water heaters, always check what is included before ordering. Supply-only product pricing generally does not include installation, gas work, electrical work, pipework changes, valves, drainage changes, old unit removal, disposal or compliance upgrades unless those items are clearly selected or included.

If ordering supply only, confirm the selected unit with your licensed installer before purchase, especially for gas type, flow rate and installation location.

Instant hot water systems 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 options include:

• 16 L/min instant gas hot water systems

• 20 L/min instant gas hot water systems

• 26 L/min instant gas hot water systems

• Natural gas continuous flow systems

• LPG continuous flow systems

• Selected brand options from Rinnai, Rheem and other available ranges

Before ordering, check the product page, installation availability, delivery options and any required add-ons for your property.

What to check before ordering an instant water heater

Before ordering an instant hot water system, check:

• Current hot water system type

• Current unit size or L/min rating

• Natural gas or LPG

• Number of bathrooms

• Number of people in the home

• Whether two showers are used at once

• Water pressure

• Gas pipe sizing

• Indoor or outdoor location

• Existing controller setup

• Access for replacement

• Required valves

• Electrical connection

• Drainage

• Whether you need supply only or supplied and installed

These checks help prevent ordering the wrong system or choosing a unit that does not suit the home.

Common mistake: choosing instant hot water only because it sounds unlimited

Instant hot water systems can keep heating water while water flows, but they are not unlimited in every sense. They have a maximum flow rate.

If the home uses more hot water at once than the system can supply, performance can drop. This is why sizing and flow rate matter.

Common mistake: choosing the wrong gas type

Natural gas and LPG systems are different. Choosing the wrong model can delay installation and create compliance issues.

Always confirm gas type before ordering. Do not assume the existing unit is natural gas just because it is connected to gas.

Common mistake: replacing electric storage with instant gas without checking extras

Changing from electric storage to instant gas may involve more than buying a gas unit.

The property may need gas pipework, electrical connection, wall mounting, pipework changes, valves, drainage and compliance upgrades. These extras can affect cost and suitability.

Common mistake: expecting instant hot water at the tap immediately

An instant water heater heats water on demand, but pipe distance still matters. If the unit is far from the bathroom, you may still wait for hot water to arrive.

For faster delivery, the system location and plumbing layout matter as much as the unit type.

Final recommendation

Instant water heating systems can be a good choice for Australian homes where the property has suitable gas supply, water pressure, external location and hot water demand. For many households, a continuous flow gas hot water system is the main instant option to compare.

A 16 L/min unit may suit smaller homes, while 20 L/min and 26 L/min systems may suit higher-demand homes depending on bathrooms, simultaneous use and gas supply. Homes without gas may be better suited to electric storage hot water or heat pump hot water, depending on the property.

The best instant water heater is not just the biggest or cheapest model. It is the one that matches your gas type, flow rate needs, household size, location and installation requirements.

To compare suitable options, browse the Installed Today hot water systems range and the instant gas hot water systems collection.

Long-tail FAQs

What is an instant water heating system?

An instant water heating system heats water only when a hot tap or shower is turned on. It does not store hot water in a tank. Gas versions are commonly called continuous flow gas hot water systems.

Is instant hot water the same as tankless hot water?

Yes, instant, instantaneous, tankless and continuous flow hot water are often used to describe systems that heat water on demand instead of storing hot water in a cylinder.

Is instant hot water actually instant?

The system starts heating water when 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 instant gas hot water system do I need?

A small one-bathroom home may suit 16 L/min, while a larger home may compare 20 L/min or 26 L/min systems. The right size depends on bathrooms, people, simultaneous use, water pressure and gas supply.

Is instant gas hot water good for two bathrooms?

Instant gas hot water can suit two-bathroom homes when correctly sized. A 26 L/min system is commonly compared, but suitability depends on gas pipe sizing, water pressure and whether two showers are used at once.

Is instant electric hot water good for a whole house?

Instant electric hot water can suit some applications, but whole-home use may require significant electrical capacity. For many homes without gas, electric storage or heat pump hot water may be more practical.

Can I replace my electric hot water system with instant gas?

You may be able to, but it can involve gas pipework, electrical connection, pipework changes, valves, drainage and compliance checks. It is usually simpler where the home already has suitable gas supply.

Do instant water heaters need maintenance?

Yes. Instant water heaters may need filter cleaning, inspection, flushing or descaling depending on water quality and manufacturer guidance. Gas units should be serviced by qualified technicians.

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

No. Natural gas and LPG systems are different and must be matched to the property’s fuel type. Always choose the correct model before ordering.

Are instant water heaters better than storage hot water systems?

They can be better for some homes, especially where space is limited or gas continuous flow suits the property. Storage systems may be better where gas is not available, where a simple electric replacement is needed, or where the household prefers stored capacity.