2024 Best Instant Gas Hot Water System: Top 10 Continuous Flow Systems Compared

Choosing the best instant gas hot water system in 2024 comes down to more than picking the biggest flow rate or the most familiar brand. The right system needs to match your home’s gas type, household size, bathroom count, water pressure, gas pipe sizing, installation location, hot water habits and budget.

Instant gas hot water systems, also called continuous flow gas hot water systems, heat water as it passes through the unit. They do not store hot water in a tank, which makes them compact, wall-mounted and practical for many homes already using natural gas or LPG.

For customers comparing systems online, Installed Today’s Instant Gas Hot Water Systems category is the best starting point. You can also compare 26L Instant Gas Hot Water Systems, Gas Hot Water Systems, Rinnai Hot Water Systems, Rheem Hot Water Systems and Bosch Hot Water Systems before ordering.

Quick Answer

Best overall 26L instant gas option: Rinnai Infinity B26 Natural Gas or LPG

Best value-focused 26L option: Rheem 26L Natural Gas or LPG

Best 20L middle-ground option: Rheem 20L or Rinnai Infinity B20

Best compact 16L option: Rheem 16L or Rinnai Infinity B16

Best hydropowered compact option: Bosch 16H Natural Gas or LPG

Best category to start with: Instant Gas Hot Water Systems

Best larger household category: 26L Instant Gas Hot Water Systems

Main thing to avoid: ordering the wrong gas type

Best alternative to compare: Gas Hot Water Systems if you are unsure whether storage gas or instant gas is better for your home

Top 10 Instant Gas Hot Water Systems for 2024

1. Rinnai Infinity B26 Natural Gas Hot Water System

The Rinnai Infinity B26 Natural Gas Hot Water System is one of the strongest overall choices for homes connected to mains natural gas.

It is a 26L continuous flow system, which makes it a common option for family homes, larger townhouses and properties with higher hot water demand. It is often compared by homeowners replacing an older Rinnai Infinity, Bosch, Rheem or Dux continuous flow system.

The Rinnai B26 Natural Gas may suit:

family homes
homes connected to mains natural gas
properties replacing an older 26L gas continuous flow unit
households with higher shower demand
homes with one or two bathrooms, depending on usage and site conditions
customers who prefer the Rinnai brand
customers wanting a compact wall-mounted system

The main advantage is strong brand recognition and practical 26L flow capacity. The main thing to check is whether the property has suitable gas supply, pipe sizing, water pressure and external wall space.

2. Rinnai Infinity B26 LPG Gas Hot Water System

The Rinnai Infinity B26 LPG Gas Hot Water System is the LPG version for homes using bottled gas.

This is important because natural gas and LPG systems are not interchangeable. If your property uses gas bottles, you need the LPG model, not the natural gas model.

The Rinnai B26 LPG may suit:

homes using bottled LPG
acreage or semi-rural properties
larger granny flats or secondary dwellings
homes replacing an existing LPG continuous flow unit
households wanting a 26L LPG system
customers who prefer Rinnai
properties with suitable LPG supply and regulator setup

Before ordering, confirm the gas type, regulator, pipe sizing, water pressure and installation location with your licensed gas fitter.

3. Rheem 26L Natural Gas Hot Water System

The Rheem 26L Natural Gas Hot Water System is a strong value-focused alternative to Rinnai in the 26L instant gas category.

It is commonly compared by customers who want a recognised major hot water brand, but do not necessarily want to pay more for a Rinnai system.

The Rheem 26L Natural Gas may suit:

natural gas homes
families comparing 26L continuous flow systems
customers replacing an older Rheem gas unit
homes needing a compact external wall-mounted system
rental properties with higher hot water demand
customers wanting a practical 26L alternative to Rinnai

The main advantage is value in the 26L category. The main thing to check is whether 26L suits the home and whether the gas supply can support the selected model.

4. Rheem 26L LPG Gas Hot Water System

The Rheem 26L LPG Gas Hot Water System is the LPG version for bottled gas properties needing a larger instant gas option.

It may suit:

LPG homes
properties replacing an older LPG continuous flow system
medium to larger households
customers wanting a 26L Rheem option
rental properties using bottled gas
homes where a 16L or 20L LPG unit may not be enough

The main advantage is a 26L LPG option at a practical price point. The main limitation is that LPG supply, regulator setup and pipe sizing need to be confirmed before ordering.

5. Rinnai Infinity B20 LPG Gas Hot Water System

The Rinnai Infinity B20 LPG Gas Hot Water System is a middle-ground option for LPG homes that do not need a full 26L system.

A 20L system can be a good fit for smaller households, townhouses, granny flats or homes with moderate hot water demand.

The Rinnai B20 LPG may suit:

bottled LPG homes
smaller houses
townhouses
one-bathroom homes
moderate hot water demand
customers replacing an older 20L LPG continuous flow unit
customers wanting a Rinnai system without stepping up to 26L

The main advantage is balance. It offers more flow capacity than a 16L unit, while usually being more compact and lower priced than many 26L systems.

6. Rheem 20L Natural Gas Hot Water System

The Rheem 20L Natural Gas Hot Water System is a practical mid-size continuous flow system for homes connected to mains natural gas.

It may suit:

small to medium households
homes with one main bathroom
townhouses
rental properties
customers replacing an older 20L natural gas system
properties where a 26L model may be more than needed

The Rheem 20L Natural Gas system is a good comparison point for customers who want a continuous flow gas system but do not need the larger 26L category.

7. Rheem 20L LPG Gas Hot Water System

The Rheem 20L LPG Gas Hot Water System is the LPG option for households that need a practical middle-ground continuous flow system.

It may suit:

bottled LPG properties
small to medium households
homes with moderate daily hot water use
rental properties
customers replacing a similar 20L LPG unit
homes where 16L may be too small and 26L may be unnecessary

The key checks are LPG supply, regulator condition, pipe sizing, water pressure, external wall location and whether the home’s expected demand suits 20L flow capacity.

8. Rinnai Infinity B16 Natural Gas or LPG Hot Water System

The Rinnai Infinity B16 range is a compact continuous flow option for smaller homes and lower-demand applications.

The Rinnai Infinity B16 Natural Gas Hot Water System and Rinnai Infinity B16 LPG Gas Hot Water System are worth comparing when a 20L or 26L system is not required.

The Rinnai B16 may suit:

smaller homes
units
townhouses
granny flats
couples
single-person homes
lower hot water demand
like-for-like 16L replacements

The main advantage is compact sizing from a recognised brand. The main limitation is flow rate. A 16L system is not usually the best fit for larger households or homes where multiple hot water outlets are used at the same time.

9. Rheem 16L Natural Gas or LPG Hot Water System

The Rheem 16L continuous flow range is another strong compact option for smaller homes.

Installed Today currently lists options such as the Rheem 16L Natural Gas Hot Water System, with LPG versions also available through the Instant Gas Hot Water Systems category where stocked.

The Rheem 16L may suit:

smaller homes
units
granny flats
one-bathroom homes
low to moderate hot water demand
budget-conscious replacements
customers comparing compact Rheem and Rinnai options

The main advantage is value in the compact category. The main thing to avoid is choosing 16L if the household actually needs 20L or 26L performance.

10. Bosch 16H Natural Gas or LPG Hot Water System

The Bosch 16H is a hydropowered instant gas hot water option commonly compared by customers replacing older Bosch units or wanting a compact continuous flow gas system.

Installed Today currently lists the Bosch 16H Natural Gas Hot Water System and Bosch 16H LPG Gas Hot Water System.

The Bosch 16H may suit:

smaller homes
units
townhouses
customers replacing an existing Bosch system
homes wanting a hydropowered-style ignition setup
natural gas or LPG properties, depending on model
lower to moderate hot water demand

The main advantage is Bosch’s compact hydropowered continuous flow style. The main limitation is that 16L capacity may not suit larger households, and the property still needs correct gas type, water pressure, flow rate and external installation conditions.

2024 Instant Gas Hot Water Comparison Table

System	Best For	Main Advantage	Main Limitation
Rinnai B26 Natural Gas	Larger natural gas homes	Strong 26L Rinnai option	Needs suitable gas supply
Rinnai B26 LPG	Larger LPG homes	26L Rinnai option for bottled gas	LPG setup must be checked
Rheem 26L Natural Gas	Value-focused 26L natural gas replacement	Competitive price and major brand	Site must support 26L demand
Rheem 26L LPG	Value-focused 26L LPG replacement	Strong LPG alternative to Rinnai	LPG costs and pipe sizing matter
Rinnai B20 LPG	Moderate LPG households	Good middle-ground flow rate	Not as strong as 26L
Rheem 20L Natural Gas	Small to medium natural gas homes	Practical mid-size option	May not suit high simultaneous use
Rheem 20L LPG	Small to medium LPG homes	Balanced LPG option	LPG setup must suit
Rinnai B16 Natural Gas/LPG	Smaller homes wanting Rinnai	Compact recognised-brand option	Lower flow capacity
Rheem 16L Natural Gas/LPG	Budget-focused compact replacement	Value compact option	Not ideal for larger homes
Bosch 16H Natural Gas/LPG	Compact Bosch replacement	Hydropowered-style Bosch option	Lower flow capacity

What Is an Instant Gas Hot Water System?

An instant gas hot water system heats water only when a hot tap or shower is turned on.

Cold water passes through the unit. The gas burner activates. The water is heated as it flows through the heat exchanger, then delivered to the tap or shower.

Unlike gas storage hot water, there is no large storage tank holding hot water. This makes instant gas systems compact and commonly installed externally on a wall.

Instant gas systems are usually compared by litres per minute, such as:

16L
20L
26L

The right size depends on the property, not just the number printed on the unit.

16L vs 20L vs 26L Instant Gas Hot Water

Choosing the right flow rate is one of the most important parts of buying an instant gas system.

A 16L system may suit:

small homes
units
granny flats
single occupants
couples
lower hot water demand
one-bathroom properties

A 20L system may suit:

small to medium homes
townhouses
moderate hot water demand
one to two bathroom properties, depending on usage
like-for-like 20L replacements

A 26L system may suit:

family homes
larger townhouses
higher hot water demand
homes with more frequent shower use
properties replacing an older 26L system
customers wanting stronger flow capacity

A 26L system is not automatically better. If the gas supply, pipe sizing or water pressure cannot support it, the system may not perform as expected.

Natural Gas vs LPG: Do Not Order the Wrong Model

Natural gas and LPG are different.

Natural gas systems are for homes connected to mains gas.

LPG systems are for homes using bottled gas.

The two are not interchangeable.

Before ordering, check:

the existing system label
your gas bill
whether there are gas bottles on site
the selected product page
your installer’s recommendation
whether the gas regulator and pipework suit the new model

Ordering the wrong gas type can delay installation, require product exchange or create extra costs.

Instant Gas vs Gas Storage Hot Water

Instant gas and gas storage both use gas, but they work differently.

Instant gas heats water as it flows through the unit. Gas storage heats and stores water inside a tank.

Feature	Instant Gas	Gas Storage
Hot water method	Heats water as it flows	Heats and stores water
Tank	No	Yes
Space	Compact wall-mounted unit	Tank footprint
Best suited to	Continuous flow replacement	Like-for-like storage replacement
Key check	Flow rate, gas supply, pipe sizing	Tank size and recovery

Choose instant gas if you want compact continuous flow hot water and the site supports it.

Choose gas storage if your old gas storage system worked well and you prefer a tank-style replacement.

For storage comparisons, start with Gas Hot Water Systems, 130/135L Gas Hot Water Systems or 160/170L Gas Hot Water Systems.

Instant Gas vs Electric Hot Water

Instant gas may suit homes already using natural gas or LPG. Electric hot water may suit homes without gas or customers wanting a simple storage tank replacement.

Instant gas may be better when:

the home already has gas
the existing system is continuous flow gas
space is limited
a storage tank is not preferred
the household wants wall-mounted hot water
gas supply and pipe sizing are suitable

Electric storage may be better when:

the home does not have gas
a simple tank replacement is preferred
the customer wants quiet operation
upfront cost is the priority
the existing electric setup already works

Heat pump hot water should also be compared if the household wants lower running cost potential and has suitable outdoor space.

Instant Gas vs Heat Pump Hot Water

Heat pump hot water is the main alternative to compare if the goal is reducing gas use or using rooftop solar power.

Instant gas may be better if:

the home already has natural gas or LPG
the current instant gas setup worked well
the customer wants compact wall-mounted hot water
the household does not want a storage tank
gas supply and water pressure are suitable

Heat pump hot water may be better if:

the home has rooftop solar
the customer wants to reduce gas use
there is suitable outdoor space
airflow and drainage are available
noise placement can be managed
a storage-style system is acceptable

Compare Heat Pump Hot Water Systems if long-term running cost potential matters more than staying with gas.

Installation Requirements for Instant Gas Hot Water

Instant gas hot water installation should only be handled by licensed professionals.

Before ordering, the installer needs to check:

gas type
flow rate
gas pipe sizing
water pressure
installation location
external wall space
clearances
ventilation
drainage
valves
controller wiring if relevant
electrical supply where required
connection positions
old system removal
current compliance requirements

A like-for-like replacement can still need extra work if the old installation does not meet current requirements.

External vs Internal Instant Gas Systems

Most standard residential instant gas systems sold for outdoor replacement are external units.

Do not install an external gas unit indoors.

Indoor gas appliances need the correct internal/flued model, correct ventilation, flueing and compliance setup.

Before ordering, confirm whether the existing system is:

external wall-mounted
internal/flued
under-house
in a garage
in a restricted space
inside a recess box

If the existing unit is not a standard external installation, the job may need extra checks before ordering.

Supply Only vs Supplied and Installed

Installed Today offers supply-only ordering for customers who already have their own licensed plumber or gas fitter arranged.

Supply-only pricing is for the product only and does not include installation, valves, gas work, electrical work, pipework changes, power point changes, drainage work, old unit removal, disposal, wall mounting changes, recess boxes, pipe covers, controller wiring or compliance upgrades unless those options are clearly selected or shown on the product page.

Supplied-and-installed options may be available on selected instant gas hot water systems in eligible Brisbane and Gold Coast service areas.

Availability depends on:

product
address
existing system
gas type
access
gas supply
pipe sizing
water pressure
electrical requirements
drainage
clearances
required extras

Before ordering supply only, make sure your licensed installer confirms the selected system suits the property.

Brisbane and Gold Coast Buying Context

For Brisbane and Gold Coast homes, instant gas systems are commonly chosen where the property already has natural gas or LPG and an existing external continuous flow unit.

Local homes should check:

natural gas or LPG
current system flow rate
current system brand and model
number of bathrooms
shower habits
water pressure
gas pipe sizing
installation location
external wall space
valve condition
clearances
drainage
whether controllers are needed
whether supplied-and-installed is available for the address

In South East Queensland, 20L and 26L systems are commonly compared for family homes, while 16L systems may suit smaller homes, units and granny flats.

Common Instant Gas Hot Water Problems

Common issues with instant gas systems include:

no hot water
hot water cutting in and out
temperature fluctuation
low flow
fault codes
gas supply issues
undersized gas pipework
blocked inlet filters
water pressure problems
controller faults
incorrect gas type
clearance or ventilation issues
electrical connection problems

Some problems are caused by the unit, but many are caused by the site. Gas supply, water pressure, pipe sizing, valves, filters and installation location all affect performance.

Gas hot water faults should be inspected by licensed professionals.

Maintenance and Longevity

Instant gas systems are compact and practical, but they still need maintenance.

Maintenance may include:

checking for fault codes
monitoring temperature consistency
keeping the unit clear of obstructions
checking water filters where required
checking valves
checking gas supply
checking controller operation
servicing according to manufacturer instructions
having leaks inspected quickly
keeping outdoor units accessible

Regular servicing can help identify problems before they become major failures.

Common Mistakes When Choosing Instant Gas Hot Water

Choosing 26L when the gas pipework cannot support it

A larger system still needs suitable gas supply.

Ordering natural gas instead of LPG

This is one of the most common and costly mistakes.

Replacing a 16L system with another 16L when the household has grown

If the old system struggled, the same flow rate may not fix the problem.

Ignoring water pressure

Flow rate depends on water pressure and site conditions, not just product size.

Assuming all systems fit the same space

Connection positions, clearances, wall space and access can vary.

Buying supply only without installer confirmation

Your licensed installer should confirm suitability before the product is ordered.

Assuming external systems can be installed indoors

External gas systems are outdoor units unless the manufacturer specifically approves another installation type.

Before Ordering Checklist

Before ordering an instant gas hot water system, check:

natural gas or LPG
existing system brand
existing flow rate
current model number
household size
number of bathrooms
shower habits
whether multiple outlets run at once
water pressure
gas pipe sizing
installation location
external wall space
clearance requirements
valve condition
electrical requirements
controller requirements
access for removal and installation
whether supply only or supplied and installed is needed
licensed installer confirmation

This helps avoid ordering the wrong size, wrong gas type or wrong system for the home.

Which Instant Gas Hot Water System Should You Choose?

Choose the Rinnai Infinity B26 if you want the strongest overall 26L comparison point and prefer Rinnai.

Choose the Rheem 26L if you want a value-focused 26L continuous flow alternative.

Choose a 20L system if the home has moderate demand and does not need a 26L unit.

Choose a 16L system if the property is smaller, lower demand or replacing a 16L unit that already worked well.

Choose Bosch 16H if you are replacing an existing Bosch-style system or want a compact hydropowered Bosch comparison.

Choose natural gas only if your home is connected to mains gas.

Choose LPG only if your home uses bottled gas.

For most customers, the safest starting point is Installed Today’s Instant Gas Hot Water Systems category, then narrowing down by gas type, flow rate and household demand.

Long-Tail FAQs

What is the best instant gas hot water system in 2024?

The best instant gas hot water system depends on the home. For larger households, Rinnai B26 and Rheem 26L systems are strong options. For medium demand, 20L systems can be a good fit. For smaller homes, 16L systems may be enough.

Is Rinnai better than Rheem for instant gas hot water?

Rinnai may suit customers who prefer strong brand recognition and the Infinity range. Rheem may suit customers wanting a recognised brand at a more value-focused price point. The better option depends on size, gas type, warranty, price and installation suitability.

Is a 26L instant gas hot water system enough for a family?

A 26L system can suit many family homes, but it depends on shower flow rates, number of bathrooms, gas supply, water pressure, pipe sizing and simultaneous hot water use.

Should I choose 16L, 20L or 26L instant gas?

Choose 16L for smaller homes and lower demand, 20L for moderate demand, and 26L for larger homes or higher demand. The correct size still depends on the property and installer confirmation.

Is instant gas better than gas storage?

Instant gas may be better if you want compact continuous flow hot water and the property has suitable gas supply. Gas storage may be better if your existing storage system worked well and you prefer a tank-style replacement.

Is instant gas hot water unlimited?

Instant gas can continue heating water while gas, water and power supply are suitable. However, performance still depends on flow rate, incoming water temperature, water pressure, gas supply and how many outlets are used at once.

Does instant gas hot water need electricity?

Many modern instant gas systems need electricity for ignition and controls. Bosch hydropowered-style models may reduce reliance on a standard power point, but installation requirements still need to be checked for the specific model.

Can I replace gas storage with instant gas?

Sometimes, but it is not always a simple swap. The job may need wall mounting, gas pipe sizing checks, pipework changes, valves, electrical work, drainage changes or compliance upgrades.

Can I buy an instant gas hot water system supply only?

Yes. Supply only is suitable if you already have your own licensed plumber or gas fitter arranged. The product price is for the unit only and does not include installation or extras unless selected separately.

Can I order an instant gas system supplied and installed?

Supplied-and-installed options may be available on selected products in eligible Brisbane and Gold Coast service areas. Availability depends on the product, address, access, gas type, existing setup and required extras.

Final Word

The best instant gas hot water system in 2024 depends on the home, not just the brand.

Rinnai B26 is a strong overall 26L option for customers who prefer Rinnai. Rheem 26L is a practical value-focused alternative. Rinnai and Rheem 20L systems suit moderate-demand homes. Rinnai and Rheem 16L systems suit smaller homes and lower-demand replacements. Bosch 16H is worth comparing for compact hydropowered-style continuous flow gas hot water.

The most important checks are gas type, flow rate, household demand, gas pipe sizing, water pressure and installation location.

Start with Installed Today’s Instant Gas Hot Water Systems, compare 26L Instant Gas Hot Water Systems, review Rinnai Hot Water Systems, browse Rheem Hot Water Systems, or compare Bosch Hot Water Systems before ordering.