Hot Water Systems

Instant & Continuous Flow Gas Hot Water

Endless hot water, nothing wasted keeping a tank warm, and a compact unit on the wall. Here's how an instant hot water system works, how it's sized by flow rate, and the models we supply and install.

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How it works

What an instant hot water system actually is

An instant hot water system — also called a continuous flow or instantaneous system — heats water the moment you turn on the tap, instead of storing it in a tank. A gas burner fires as water flows through, delivering hot water for as long as you need it and shutting off the instant you stop.

That means two things people love: you never run out of hot water mid-shower, and there's no tank of water sitting there losing heat and costing you money. The unit is compact and wall-mounted, so it frees up the space a storage tank would take.

See also: what size

Compact continuous flow gas hot water unit mounted on an exterior wall
On demand

How continuous flow heats water on demand

There's no tank and no waiting — here's what happens the moment you open a hot tap.

1 · You open a tapA flow sensor detects water moving through the unit and fires the gas burner.
2 · It heats as it flowsWater passes through a heat exchanger and is heated to your set temperature on the way to the tap.
3 · Endless hot waterAs long as the tap is running, it keeps heating — you can't drain a tank that isn't there.
4 · It shuts offClose the tap and the burner stops instantly, so no gas is spent keeping water warm.
Diagram of water flowing through a continuous flow heat exchanger to the tap
No tank, no standing loss — the burner fires only while you're using hot water.
Sizing

Sizing by flow rate — how many bathrooms?

Continuous flow units are rated by flow rate in litres per minute (L/min). The right size is about how much hot water you draw at once.

Unit sizeFlow rateSuits
Compact~16 L/minA single bathroom, smaller homes, units/apartments
Mid~20 L/minMost homes — a bathroom plus kitchen at once
Large~26 L/minMultiple bathrooms running together, larger households

See also: Rinnai Infinity 26

Getting it right

Running multiple outlets, and running costs

Two things decide whether you're happy with a continuous flow system — and both come down to sizing it correctly.

Single vs multi-bathroom

A single-bathroom home is well served by a compact unit; run two showers at once and you need the flow rate to match, or the temperature drops. We size on how your household actually uses hot water, not a guess.

Endless, but sized

"Continuous" means it won't run out — but it can only heat so much water per minute. The right flow rate is what lets everyone get hot water at the same time without it going cool.

Running costs

With no tank losing heat, a continuous flow gas unit is typically cheaper to run than gas storage. On gas, it's one of the more economical ways to deliver endless hot water.

Supply & install

The units we install — and how we size yours

The model matters; sizing it right matters more.

We supply and install continuous flow gas systems across Sydney, including the proven Rinnai Infinity range and the Rinnai B26. Rinnai leads this category for a reason — reliable units, strong flow rates, and parts and service support that last.

The single most important thing is sizing. We look at your bathrooms, your peak usage and your gas supply, then recommend the flow rate that gives everyone hot water at once without going cool. You get an itemised quote — the unit, the install, and any site extras shown separately.

If you know you want endless hot water and a compact unit, see the Rinnai B26, or let us match the right model to your home.

See also: Rinnai B26

Licensed gasfitter installing a continuous flow gas hot water unit in Sydney
Supplied, sized and installed to code by licensed gasfitters, Sydney-wide.
Shop the range

Popular continuous flow gas systems

A selection of the continuous flow gas systems we supply and install across Sydney. Prices are for the unit — our licensed team quotes the install once we see the site.

See all 23 continuous flow systems
FAQ

Instant & continuous flow questions, answered

The questions we're asked most about continuous flow systems.

How does continuous flow (instant) hot water work?
It heats water as it flows, the moment you open a hot tap — a gas burner fires while water passes through a heat exchanger, and stops the instant you close the tap. There's no tank, so it never runs out and wastes no heat standing by.
What size continuous flow unit do I need?
It's sized by flow rate (litres per minute) and how many outlets you run at once — roughly 16 L/min for a single bathroom, 20 L/min for most homes, and 26 L/min for multiple bathrooms together. We size it to your household as part of the quote.
Will it run two bathrooms at once?
Yes, if it's sized for it. A larger unit (around 26 L/min) is built to run multiple showers together without the temperature dropping. Under-size it and the water goes cool when demand peaks — which is why correct sizing matters.
How long do instant gas hot water systems last?
A quality continuous flow gas unit often lasts longer than a storage tank — commonly 12–20 years with servicing — because there's no tank to corrode. Keeping the right water pressure and servicing it helps.
Is continuous flow cheaper to run than gas storage?
Usually, yes — with no tank losing heat while it sits there, a continuous flow gas unit wastes less energy, so it typically costs less to run than gas storage for the same household.
Do you supply and install continuous flow systems?
Yes — we help you choose the right model and flow rate, supply it, install it to code, and remove the old unit. One team, Sydney-wide, and we come to you.
Want endless hot water?

Get a continuous flow quote

We'll size the right flow rate for your home, supply the unit and install it to code — itemised pricing, Sydney-wide, and we come to you.

Call 1300 096 668