Continuous flow, also called instantaneous, is the wall-mounted gas unit that heats water only while a tap is running. No tank, no running out, no standing loss keeping a tank warm at three in the morning. Here is what it costs installed and what to check before you commit.
Continuous flow hot water installed: the price
| Job | Price | What it covers |
|---|---|---|
| Gas continuous flow, supply and install | $1,900 to $3,500 supply + install | Wall-mounted unit, connection to gas, water and power, valves, commissioning, gas compliance certificate and Form 4 |
| Gas line upgrade if the existing supply is too small | Quoted on inspection | Only needed on some storage-to-continuous-flow swaps; we measure before we quote |
| Repair to an existing continuous flow unit | Quoted after diagnosis | Error codes, ignition and sensor faults. No published figure |
| Gas storage, for comparison | $1,800 to $3,200 supply + install | Tank with a burner, fast recovery |
| Heat pump, for comparison | $2,500 to $4,500 supply + install after STC rebates | Cheapest to run, needs power and airflow, not gas |
Why is continuous flow sized by flow rate, not litres?
Because there is no tank to fill. A storage system is described by how much hot water it holds, and a continuous flow unit is described by how many litres a minute it can heat as the water passes through. A small unit will run one shower comfortably and struggle when the kitchen tap opens at the same time. A high-flow unit will run two showers and a washing machine together without the temperature dropping. So the question we ask is not how many people live in the house but how many hot taps are likely to be open at once, which for a big family on a school morning is more than you would think. That is why a big household needs a high-flow unit, and why the high-flow unit sits at the top of the range. Fitting a unit one size too small to save money is the most common mistake we see with continuous flow, and the symptom is a shower that goes lukewarm whenever someone else uses hot water.
Where does a continuous flow job land in the range?
The unit size is the main driver: a compact unit for a couple costs less than a high-flow unit for a household of five or six. After that, it is what the unit is replacing. A continuous flow unit replacing another continuous flow unit in the same spot is the cheapest job, because the gas line, the mounting and the pipework are already right. Swapping from a storage tank to continuous flow costs more, because the unit hangs on a wall rather than standing on a pad, so the hot and cold connections move, the old tank comes out, and the unit needs a power point close by for its ignition and controls. The last driver is the gas line, covered below. Coastal positions get the salt-rated fittings, which is a small premium.
Will I need a bigger gas line?
Sometimes, and this is the one to get answered before anyone quotes a number. A continuous flow unit heats water very quickly, which means it draws a lot of gas for the few minutes it is running, considerably more than the burner under a storage tank. The gas supply pipe from the meter, or from the LPG bottles, was sized for the old appliance. If it is too small for the new one, the unit will not get the gas it needs at full flow, and it will be starved on cold mornings when you want it most. A licensed gas fitter measures the existing line and the total gas load on the property and tells you whether it copes. If it needs upgrading, that is quoted on inspection, because the length of the run and how it is routed decide the cost, and we will not invent a figure for it here. If the house already runs continuous flow, this is rarely an issue. If it runs gas storage or is coming off electric, ask about it before you accept a quote, and be wary of any quote that has not looked.
What sits inside the $1,900 to $3,500
The unit with its warranty registered to you, delivery, removal of the old unit, wall mounting and flue arrangement to the standard, connection to gas, cold and hot water, a tempering valve where required so bathroom taps stay at 50 degrees or below, isolation valves, connection to a nearby power point, commissioning and a temperature check at the taps, the gas compliance certificate and the Form 4. In Queensland the plumbing side of a like-for-like hot water replacement is notifiable work, lodged with the QBCC by the licensed plumber on a Form 4. The gas side must be done by a licensed gas fitter, who issues the compliance certificate. Our QBCC plumbing licence is 15243081, and the gas work is done under a separate Queensland gas work licence. Both pieces of paper come with the job.
Is continuous flow the right choice for my house?
It suits a home that already has gas, a household that staggers showers through the evening, anyone who has been running out with a tank, and anyone short on space, because a wall unit frees up the pad the tank stood on. The endless hot water is real, within the unit's flow rate. Two honest cautions. First, there is a short delay before hot water arrives at the tap, longer on a long pipe run, which some people find annoying on a hand basin. Second, if the house has no gas, running a new gas supply for one appliance is rarely the best money, and a heat pump at $2,500 to $4,500 after STC rebates is usually the better call, with STCs and any state rebate taking $1,000 to $2,500 off the sticker. If your home has rooftop solar, that comparison deserves a proper look before you commit to gas.
Should I repair the old unit instead?
Often, yes. Continuous flow units show an error code when something is wrong, and many of those codes point to a sensor, a fan or an ignition part that is repairable, with the price quoted after diagnosis. Note the code, try one power cycle, and if it comes straight back, call. A unit that is old enough for parts to be hard to find, or that is corroding through on a coastal wall, is a replacement rather than a repair, and we will tell you which before you spend anything.
Thinking about continuous flow, or yours has thrown a code? Call Hills Plumbing & Gas on 0472 657 042 or book through our Hot Water Systems service page. I will size the unit to how your house actually uses hot water, check the gas line before quoting, and give you one fixed price with the compliance certificate included. Jieye.