20L Instant Gas Hot Water Systems From $1,199
You’re already looking at 20L instant gas hot water systems. We’ll show the three best suited options immediately, then refine them around efficiency, price, brand and your final buying preference.
Checking live booking options.
Find Your Best 20L Instant Gas System
The flow category is already decided. Now we’ll determine which 20L system best suits your priorities.
Prefer to discuss your hot water options onsite?
Book an onsite inspection and one of our plumbers can inspect your existing hot water system, check the installation requirements and talk you through the replacement options available for your home.
Ideal if you would prefer to have your existing system inspected and discuss the available options with a plumber before choosing your replacement.
Flexible payment options
Hot water from 4 easy payments of $324.75 on eligible purchases from $1,299. Pay securely with Zip, Afterpay, PayPal, Google Pay, Visa or Mastercard.
20L Instant Gas & Continuous Flow Hot Water Systems
20L instant gas hot water systems sit in the middle of the residential continuous-flow range. They provide more simultaneous hot water flow than compact 10L–16L systems without automatically moving the home into the larger 26L or 32L category.
A 20L system can be a strong choice for one-bathroom homes wanting extra flow headroom and selected one-to-two bathroom properties where simultaneous hot water demand remains moderate.
20L systems are also described as 20L continuous flow gas hot water systems, instantaneous gas water heaters, tankless gas water heaters and on-demand gas hot water systems.
JR Gas & Water supplies and installs 20L continuous-flow gas hot water throughout Greater Brisbane, the Gold Coast, Logan, Ipswich, Redlands, Moreton Bay and surrounding South East Queensland areas.
20L Instant Gas, Continuous Flow, Tankless & On-Demand Hot Water
These names all generally describe the same basic hot water technology: water is heated while it passes through the gas appliance rather than being stored in a tank.
| Term | Meaning |
|---|---|
| 20L Instant Gas Hot Water | Common homeowner wording for a 20L-class gas continuous-flow heater. |
| 20L Continuous Flow Gas | Common Australian industry terminology. |
| 20L Instantaneous Gas | Technical wording for the same on-demand heating principle. |
| 20L Tankless Gas Water Heater | International terminology highlighting that there is no storage cylinder. |
| 20L On-Demand Gas Hot Water | Describes the burner operating when hot water is requested. |
What Does 20L per Minute Mean?
A 20L continuous-flow unit does not contain 20 litres of stored hot water. The number describes its approximate flow class under specified temperature-rise conditions.
Incoming water enters the heater, the burner raises its temperature and the hot water leaves immediately for the fixtures being used.
No Storage Tank
There is no finite 20-litre supply waiting inside the appliance.
Continuous Duration
The system can continue producing hot water while demand remains within its available heating capacity.
Finite Simultaneous Flow
Multiple fixtures still share the available litres per minute.
Who Is a 20L Continuous Flow Gas System Best For?
Stronger One-Bathroom Homes
A useful option where a 16L system feels marginal or where other small hot water draws occasionally overlap shower use.
Selected Two-Bathroom Homes
Can suit homes with two bathrooms where simultaneous use is limited rather than two high-flow showers regularly operating together.
Townhouses
The compact wall-mounted format suits properties wanting stronger gas hot water without a storage cylinder.
Family Homes with Moderate Demand
Occupant numbers can be higher where showers are used sequentially rather than simultaneously.
Existing 20L Replacements
Often the logical first choice when the old 20L unit has historically met household demand.
Homes Not Needing 26L
Avoids unnecessarily increasing appliance size where household demand remains moderate.
16L vs 20L Continuous Flow Gas Hot Water
| Comparison | 16L | 20L |
|---|---|---|
| Main Position | Strong one-bathroom system | Moderate-demand crossover size |
| Single Shower | Strong application | Greater spare flow |
| Shower + Other Outlet | More limited | More available flow to share |
| Two Bathrooms | Usually selected around one main shower | Can suit selected two-bathroom homes with moderate overlap |
| Best Reason to Choose 20L | — | 16L is becoming marginal but 26L is unnecessary |
20L vs 26L Continuous Flow Gas Hot Water
The move from 20L to 26L is a more significant capacity increase and is normally justified by stronger simultaneous demand.
| Comparison | 20L | 26L |
|---|---|---|
| Main Category | Moderate household demand | Family / higher simultaneous flow |
| One Bathroom | Strong | Often more capacity than required |
| Two Bathrooms | Can suit moderate overlap | Stronger starting point where simultaneous use is common |
| Gas Demand | Lower than larger capacity units | Higher maximum gas demand |
| Best Reason to Upsize | — | Multiple outlets regularly operate together |
Is a 20L Gas Hot Water System Big Enough for Two Bathrooms?
It can be, but bathroom count alone is not enough to size continuous-flow gas.
A property may have two bathrooms but rarely use both showers together. In that situation, 20L can be entirely sensible. A different property may have the same two bathrooms but require both showers to operate strongly at the same time, making a larger system more appropriate.
20L May Suit When
- Two bathrooms exist but showers are normally staggered.
- One shower is the main peak demand.
- Fixture flow rates are moderate.
- Kitchen and laundry use rarely overlap heavily with showering.
- The previous 20L system has always performed adequately.
Consider 26L or Larger When
- Two showers regularly operate together.
- High-flow shower heads are used.
- Kitchen or laundry demand overlaps heavily with showers.
- Household members expect multiple fixtures to run without compromise.
- The current 20L unit already feels flow-limited.
Best 20L Instant Gas Hot Water Systems – JR Installer Picks
Best Overall
Rinnai Infinity B20
JR's current Best Overall 20L pick for homeowners wanting a modern, compact Japanese-made continuous-flow system from one of Australia's best-known gas hot water brands.
View Rinnai Infinity B20 →Strong Mainstream Performer
Rheem 20 Continuous Flow
JR's current Performer choice, with Japanese manufacture, a 20L-class flow rate and a 50°C preset configuration suited to applicable residential installations.
View Rheem 20 →Strong All-Rounder
Vulcan DuoMax 20
A practical mid-range option for moderate household demand where the customer wants more flow than a compact 16L system without moving straight to 26L.
View Vulcan DuoMax 20 →Smart-Control Option
Bosch OptiFlow 20
A modern continuous-flow option with Bosch OptiFlow technology and connected-control capability for homeowners wanting more control over their gas hot water system.
View Bosch OptiFlow 20 →Efficiency-Focused Pick
Thermann 6-Star 20L / 21R
A useful efficiency-focused option sitting around the 20L class. JR's current product data identifies the Thermann unit as the 21R, with an approximately 21L/min nominal class and a 6.1-star energy rating.
View Thermann 6-Star 20L →Budget Direction
Envirosun 20
A lower-cost 20L-class option for customers primarily focused on installed value and moderate continuous-flow performance.
View Envirosun 20 →Do Not Size a 20L Gas System by Occupant Count Alone
Continuous-flow systems do not store a fixed quantity of hot water, so occupant count is much less useful than it is with electric or gas storage tanks.
| Household Behaviour | Effect on a 20L System |
|---|---|
| Six people shower one after another | Long operating time but relatively low simultaneous flow demand |
| Two people shower together | Flow requirement increases substantially at the same moment |
| One shower + basin | Often a lighter overlapping demand |
| One shower + high-flow kitchen tap | More of the available 20L-class capacity is shared |
Temperature Rise Affects 20L Continuous Flow Performance
The 20L rating is measured under defined temperature-rise conditions. Actual flow changes depending on how much the appliance needs to increase the incoming water temperature.
Warmer Incoming Water
Requires less heat to reach the target temperature.
Colder Incoming Water
Requires more energy per litre and can reduce available heated flow.
Higher Outlet Temperature
Also increases the amount of heat required for every litre.
50°C vs 60°C 20L Continuous Flow Gas
Selected 20L-class systems are available in different outlet-temperature configurations.
JR's current Rheem 20 is a 50°C preset model, while other products may offer 50°C and 60°C configurations or controller-based arrangements.
50°C Configuration
Can provide a straightforward temperature-limited option for applicable domestic sanitary fixtures.
60°C Configuration
May suit installations needing higher distribution temperature, with appropriate downstream temperature control where required.
Does a 20L Continuous Flow System Need a Gas Supply Upgrade?
Not always, but the gas supply needs to be checked.
Moving from a similarly powered 20L unit to another 20L system may be relatively straightforward where the existing installation is suitable. Moving from a smaller 10L, 12L or 16L unit to 20L can increase maximum appliance gas demand.
Natural Gas vs LPG 20L Continuous Flow Hot Water
Applicable 20L continuous-flow systems are available in fuel-specific Natural Gas and LPG versions.
Natural Gas
Common where reticulated Natural Gas already serves the property and existing gas infrastructure is available.
LPG
Suitable where the property uses LPG, with cylinder supply, regulator arrangement and total gas demand considered as part of installation.
20L Continuous Flow Gas vs Gas Storage Hot Water
| Comparison | 20L Continuous Flow | Gas Storage |
|---|---|---|
| Storage Tank | No | Yes |
| Sizing Method | Simultaneous flow + temperature rise | Storage volume + recovery |
| Hot Water Duration | Continuous while demand remains within capacity | Depends on stored reserve and recovery |
| Footprint | Compact wall-mounted format | Ground-mounted storage cylinder |
| Standing Heat Loss | No stored cylinder | Some heat is continually lost from stored water |
Replacing an Existing 20L Instant Gas Hot Water System
If an existing 20L unit has always comfortably met household demand, a new 20L system is usually the first replacement category worth comparing.
JR Checks:
- Whether the old 20L unit actually supplied enough flow.
- Natural Gas or LPG fuel type.
- Existing gas pipe capacity.
- Hot and cold connection locations.
- Power requirements of the selected replacement.
- Existing wall position and clearances.
- 50°C or 60°C requirements.
- Whether household demand has increased.
- Whether moving to 26L would provide a genuine benefit.
Upgrading From 16L to 20L Continuous Flow Gas
Moving from 16L to 20L can be worthwhile when the smaller system is clearly struggling with overlapping demand.
That upgrade may also change gas demand and installation requirements, so it should not be treated as a guaranteed like-for-like appliance swap.
Smart Controls on 20L Continuous Flow Gas
Connected controls are available on selected 20L systems. Bosch OptiFlow, for example, sits in the smart-control direction of this category.
Wi-Fi does not increase the underlying litres-per-minute capacity. It adds control and convenience to the appliance.
How Much Does a 20L Instant Gas Hot Water System Cost?
JR displays current installed pricing in the live product grid above rather than hardcoding prices into this long-form page.
Installation Cost Can Change With:
- Brand and model selected.
- Natural Gas or LPG.
- Existing gas-pipe capacity.
- Like-for-like replacement versus an upgrade from 16L.
- Hot and cold water pipework.
- Electrical supply requirements.
- 50°C or 60°C system configuration.
- Relocation of the unit.
- Changing from gas storage or electric hot water.
- Mounting position and compliance requirements.
20L Continuous Flow Gas Installation Brisbane & Gold Coast
JR Gas & Water supplies and installs 20L instant and continuous-flow gas hot water systems throughout Brisbane and the Gold Coast.
1. Confirm Flow Requirement
Check whether 20L genuinely suits the home's simultaneous hot water demand.
2. Choose the System
Compare Rinnai, Rheem, Vulcan, Bosch, Thermann and Envirosun options.
3. Check Gas Supply
Confirm fuel type, gas-pipe capacity and appliance requirements.
4. Check Services
Assess water connections, power, mounting position and clearances.
5. Install & Connect
Complete the required gas, water, electrical and mounting work.
6. Test & Commission
Test ignition, burner performance, water flow and outlet temperature.
20L Continuous Flow Gas Hot Water Brisbane & Gold Coast
20L Instant Gas Brisbane
JR Gas & Water supplies and installs 20L continuous-flow gas hot water throughout Greater Brisbane, including Brisbane City, Brisbane North, Brisbane South, Logan, Ipswich, Redlands and surrounding areas.
The 20L category suits many medium-demand homes that need more simultaneous capacity than a 16L unit without automatically requiring 26L.
View Brisbane Hot Water Installation →20L Instant Gas Gold Coast
JR Gas & Water installs 20L instantaneous and continuous-flow gas systems throughout the Gold Coast for homes wanting compact, on-demand hot water with moderate household flow capacity.
View Gold Coast Hot Water Installation →What We Have Learned Installing 20L Continuous Flow Gas
20L Is a Genuine Crossover Size
It solves the gap between strong one-bathroom 16L systems and the larger 26L family category.
Two Bathrooms Does Not Mean Two Showers
A two-bathroom floor plan can suit 20L if the household rarely uses both showers at once.
Occupant Count Is Secondary
Flow at one moment matters far more than how many people use the appliance across the full day.
Upsizing Can Change Gas Requirements
Moving from 12L or 16L to 20L can require the existing gas supply to be reassessed.
20L Can Avoid Unnecessary 26L Oversizing
Not every two-bathroom home needs a 26L system. Actual fixture usage should decide it.
Replacement History Is Valuable
If an existing 20L heater has always comfortably supplied the home, that is strong real-world evidence that the same flow class remains appropriate.
20L Instant & Continuous Flow Gas Hot Water FAQs
Is 20L instant gas enough for one bathroom?
Yes. A 20L system provides substantial capacity for a normal one-bathroom home and can provide useful spare flow for limited overlapping hot water use.
Is a 20L gas hot water system enough for two bathrooms?
It can be where both showers are not regularly used together. If two showers need strong simultaneous flow, compare 26L or larger systems.
Can two showers run from a 20L continuous-flow system?
Potentially, depending on shower flow rates, incoming water temperature and required outlet temperature. For regular simultaneous two-shower use, JR generally prefers to assess whether a larger flow class would provide a better result.
How many people can use a 20L instant gas system?
Occupant count is not the main limitation. Multiple people can shower sequentially because there is no finite storage tank. The key limit is simultaneous hot water flow.
Does a 20L gas system store 20 litres?
No. It is a tankless continuous-flow appliance. The 20L figure refers to its flow-rate category under specified operating conditions.
Is continuous flow the same as instant gas hot water?
Yes. Continuous flow, instant gas, instantaneous gas, tankless gas and on-demand gas are common terms for the same basic hot water technology.
Can a 20L continuous-flow system run out of hot water?
It does not run empty like a storage tank. It can keep producing hot water while demand remains within its available flow and heating capacity.
Should I choose 16L or 20L instant gas?
Choose 16L for a normal one-bathroom home with limited overlapping demand. Choose 20L when additional simultaneous flow is genuinely useful.
Should I choose 20L or 26L instant gas?
Choose 20L where moderate demand is expected. Move to 26L where multiple outlets or showers regularly need stronger simultaneous hot water flow.
What is the best 20L instant gas hot water system?
JR currently positions Rinnai Infinity B20 as Best Overall, Rheem 20 as its Performer and Vulcan DuoMax 20 as its All-Rounder. Bosch OptiFlow is also relevant where connected controls are important.
Is Rinnai Infinity B20 good?
Yes. JR currently positions the B20 as its Best Overall 20L continuous-flow system and a strong middle-capacity option for moderate residential demand.
Is Rheem 20 a 50°C system?
JR's current Rheem 20 product is presented as a 50°C preset continuous-flow water heater.
Is Thermann 20 actually a 21L system?
JR's current Thermann 6-Star product sits in the 20L collection but the technical information identifies it as the Thermann 21R with an approximately 21L/min class output.
Does Bosch OptiFlow 20 have Wi-Fi?
Bosch OptiFlow 20 is offered with connected-control capability, making it the smart-control direction within JR's current 20L collection.
Can a 20L system run on LPG?
Applicable products are available in fuel-specific Natural Gas and LPG versions. The exact model must match the property's fuel supply.
Does a 20L gas heater need electricity?
Many modern 20L electronic continuous-flow systems require an electrical supply for ignition and controls. Check the exact requirements of the selected model.
Does upgrading from 16L to 20L need a bigger gas line?
It may. Gas pipe sizing depends on the new appliance demand, pipe length, gas type and other appliances connected to the system. The existing gas supply should be checked.
Can I replace my old 20L heater with another 20L?
Yes. If the previous 20L system always met household demand, another 20L-class system is normally the logical first comparison.
How much does a 20L gas hot water system cost installed?
Installed price depends on the model, gas type, existing gas supply, plumbing, power and whether the installation is like-for-like or requires upgrades. JR displays current live installed pricing above.
Do you install 20L instant gas in Brisbane and Gold Coast?
Yes. JR Gas & Water supplies and installs 20L instant and continuous-flow gas hot water throughout Greater Brisbane, the Gold Coast, Logan, Ipswich, Redlands, Moreton Bay and surrounding South East Queensland areas.
Compare Instant & Continuous Flow Gas Hot Water by Size
Choose Your 20L Continuous Flow Gas Hot Water System
Compare 20L instant gas systems, brands, flow rates, smart-control options, Natural Gas and LPG variants and current installed pricing above. If you are unsure whether your property needs 16L, 20L or 26L, book an onsite quote assessment and JR can assess the household demand and existing gas installation before you choose.