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Hot Water Systems

Gas Hot Water Systems

Gas hot water systems Sydney, Melbourne and Brisbane — gas storage and continuous-flow units, fast recovery, lower running cost than electric, mature technology, well-suited to most Australian homes. Authorised Rinnai, Rheem and Bosch installer.

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The short answer

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Gas hot water systems in Sydney are either continuous-flow units sized from 16 to 32 litres per minute or storage tanks from 130 to 360 litres, and both heat water quickly at a lower running cost than electric storage, around $500–$800 a year for a typical four-person home. AHHAC installs Rinnai, Rheem and Bosch gas units on natural gas or LPG to AS/NZS 5601, with the compliance certificate and final pressure test included.

Continuous-flow
16–32 LPM
Storage tanks
130–360 L
Running cost (4 people)
~$500–$800/yr
Warranty
10–12 years

Reviewed by the AHHAC Technical Team — licensed plumbers & hydronic engineers, NSW Lic 262528C.How we write & review

Gas hot water remains the most popular hot-water choice in Australia for a reason. Burning gas to heat water is fast (instant warm-up), inexpensive to run (gas tariffs are around a third the price of electric resistance), and the units themselves are mature, robust and inexpensive to buy. AHHAC installs both gas storage tanks and continuous-flow (instantaneous) gas units, with full STC paperwork and certificate of compliance handled in-house.

We're an authorised Rinnai, Rheem and Bosch supplier, and we also install Vulcan, Aquamax and Dux units where required. For Australian homes with three or more occupants, we almost always recommend continuous-flow over storage — never running out of hot water, a smaller wall footprint, and typically a longer manufacturer warranty.

Continuous-flow (instantaneous) vs storage

Continuous-flow units heat water on demand through a finned heat exchanger — there's no tank. You only burn gas when hot water is being drawn. Modern Rinnai Infinity, Rheem Continuous-Flow and Bosch HydroPower units sit around 6-star energy ratings and deliver up to 32 litres per minute (twin-bathroom homes).

Storage tanks (130 L to 360 L typical) maintain a reservoir of pre-heated water — fast first-draw and good for homes with surge demand (multiple morning showers at the same time). The downside is standby heat loss — even an insulated tank gives off ~15% of its stored heat per day, which the burner has to make up.

Our default recommendation: continuous-flow for 1–4 person homes with one or two bathrooms, storage for larger families with simultaneous showers and bathtub fills.

Sizing & flow rate

Continuous-flow capacity is measured in litres-per-minute at a 25 °C temperature rise (typical Australian conditions). A 26 LPM unit (Rinnai Infinity 26) handles two showers + a kitchen tap simultaneously without drop. A 32 LPM unit covers up to three bathrooms.

For storage tanks, sizing is based on the number of bathrooms and peak draw — typically 170 L for a 2-person home, 250 L for 4-person, 315 L for 5+. AHHAC sizes every install at the design stage with a 30-minute on-site flow test for retrofits.

Smart features & operating cost

The current Rinnai Sensei range adds a Wi-Fi gateway, recirculation modes (instant hot at the tap) and built-in flow monitoring — you can see exactly how much gas your hot water is using day to day. Rheem MetroMax II provides similar app control.

Operating cost on natural gas in Australia (2026 average tariffs): a typical 4-person home uses 12,000–18,000 MJ/year for hot water alone — roughly $500–$800 in gas. The same household on electric resistance hot water would spend $1,500–$2,200 a year. Switching from electric to gas continuous-flow typically pays back in 4–6 years.

STCs, rebates & install requirements

Small-scale Technology Certificates (STCs) only apply to solar and heat pump water heaters — a gas-to-gas replacement does not earn them. If you are weighing gas against a heat pump, the heat pump may attract STCs and state hot water incentives; AHHAC checks current eligibility at quote and handles the paperwork for whichever system you choose.

Installation requires a gas connection of adequate size and a compliant flue path. For continuous-flow units the unit is wall-mounted (typically outside or in a vented enclosure). Storage tanks are floor-mounted in a vented enclosure or external area. All AHHAC gas hot-water installs include certificate of compliance and final pressure testing.

Key benefits

  • Continuous-flow (instantaneous) or storage tank options
  • 6-star energy ratings on flagship models
  • Sized 16 LPM to 32 LPM continuous-flow
  • 130 L to 360 L tank capacities
  • Compatible with natural gas or LPG
  • Wi-Fi smart-app control on premium units
  • 10–12 year heat exchanger / tank warranties
  • Authorised Rinnai, Rheem and Bosch supplier
  • STC and state-rebate paperwork handled
  • Pairs with solar pre-heat for further savings
  • Recirculation modes for instant hot water at distant taps
  • Same-day install in most metro areas

Featured products & systems

Rinnai Infinity 26

Japanese-engineered 26 LPM continuous-flow gas unit. The dominant Australian choice — Wi-Fi-ready, 12-year heat exchanger warranty, handles two bathrooms simultaneously.

Rheem Metro Max II

Australian-made 26 LPM continuous-flow with built-in Wi-Fi, recirculation mode, and a market-leading 6-star energy rating.

Rinnai Sunmaster Solar Boost

Continuous-flow gas booster paired with rooftop solar collectors — 70–80% of annual hot water from the sun, gas top-up only when needed.

Rheem Stellar 360 L

Premium 360 L gas storage tank for high-demand households — vitreous enamel lined, 10-year tank warranty, fast 130 L/h recovery.

Before you upgrade

Switching to gas continuous-flow in Sydney: gas supply, flue clearances and the all-electric question

Swapping a gas storage tank for a continuous-flow unit is one of the most common gas hot water upgrades we quote in Sydney, and it is usually a good one. But a continuous-flow heater burns a lot of gas in a short burst, and that changes the installation in ways a like-for-like tank swap does not.

  • Gas supply: a storage tank sips gas over an hour, while a continuous-flow unit needs a high flow the moment a tap opens. The gas line and meter must deliver it with the cooktop and heating running, so we calculate pipe sizing under AS/NZS 5601 rather than assume the old pipe will do. An undersized supply is the usual cause of temperature that surges and drops mid-shower.
  • Flue clearances: external units must sit set distances from openable windows, doors, eaves and boundaries. On tight Sydney terraces and side passages, the old tank position is not always compliant for a new unit.
  • Water flow: the burner needs a minimum flow to fire, so very low-flow fittings or poor mains pressure can stop it lighting.
  • Power: continuous-flow units need a weatherproof power point nearby for their electronics and fan.

Then there is the bigger question of how long you will stay on gas. A well-installed gas unit gives long service, and existing Sydney homes can still be connected. But Victoria no longer allows new gas connections for most new homes, the ACT has stopped new gas network connections, and many households are moving toward all-electric as they add rooftop solar. If you expect to disconnect gas within a few years, it can make more sense to put the money into a heat pump now than to install a new gas unit you will retire early.

If gas remains the right call, we size it properly: our instantaneous hot water guide explains flow-rate sizing, and our Rinnai hot water systems page covers the continuous-flow range. If you are weighing the all-electric route, compare it with a hot water heat pump.

Written from on-site experience by the AHHAC Technical Team.

Who designs & installs this

Licensed, in-house plumbers — since 1998.

AHHAC's in-house design and service team — licensed plumbers and hydronic engineers (Lic 262528C) who have designed and installed 2,400+ hydronic heating, cooling and hot water systems across Australia since 1998.

Every plumbing and hot water job is assessed on site, carried out by our own licensed plumbers and gasfitters to AS/NZS 3500 (plumbing) and AS/NZS 5601 (gas), pressure-tested and documented, and backed by ongoing service. Nothing is subcontracted out.

  • Licensed plumbers & gasfitters on every job
  • Clear written quote before work starts
  • Rheem & Rinnai hot water authorised
  • Work tested, photographed & documented
  • Six showrooms: NSW · ACT · VIC · QLD
  • Planned maintenance for homes & strata
Read our case studies →Customer reviews →Editorial standards →
262528C
NSW plumbing licence
85 164 746 490
ABN (verifiable on ABN Lookup)
2,400+
Hydronic systems installed
Since 1998
Operating in Australia
AS/NZS 3500
Plumbing & drainage standard
AS/NZS 5601
Gas installations standard
FAQs

Common questions

Storage gas or continuous-flow gas?

For most households, continuous-flow wins: smaller footprint, never run out of hot water, longer warranty (10–12 years), more efficient. Storage gas is only better in very large households (5+ people) or where you need a big hot water buffer for multiple simultaneous draws.

Are gas systems efficient?

Modern condensing gas systems achieve 92–96% net efficiency by recovering heat from flue gases. We install Rheem and Rinnai units rated 5+ stars by the Australian Energy Rating Scheme.

Can I run gas hot water on LPG (no mains gas)?

Yes — most major models work on LPG with a simple conversion kit. We install LPG hot water across regional areas and properties not connected to natural gas mains.

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Reviews

Trusted by homeowners, builders and strata across Australia

★★★★★
Rated 5-star across NSW · ACT · VIC · QLD
★★★★★

"AHHAC delivered our 22-zone underfloor system on time, on budget and to spec. The crew were tidy, the documentation was thorough, and the commissioning was textbook."

David Chen
Custom Builder · Mosman, NSW
★★★★★

"We've worked with AHHAC for 17 years. They've installed and serviced our hot water plant across three commercial buildings — and they pick up the phone on weekends."

James Holloway
Strata Manager · Melbourne CBD
★★★★★

"Three mobs quoted us; AHHAC's design was the only one based on a proper heat-loss calculation. The system runs beautifully — the others would've been oversized and expensive."

Janelle Smith
Homeowner · Robina, QLD
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Last updated Content reviewed by the AHHAC Technical Team (NSW plumbing licence 262528C)Editorial standards