Installing a Gas Tankless Water Heater Safely in Australian Homes

Australian households use 150–200 litres of warm water daily, especially during Melbourne, Hobart and alpine winters. A correctly sized gas continuous flow unit can cut energy bills by 20–30% compared with a storage cylinder, particularly when paired with rooftop solar that offsets the small electrical draw for ignition and the inbuilt fan.

Because the appliance combines gas, flame and exhaust, installation is regulated work. The job must follow AS/NZS 5601 and be carried out by a licensed gas fitter, then tested, signed off and recorded with the local distributor such as Jemena in Sydney or Multinet in Melbourne.

Assessing hot water demand before you buy

Walk through the home at peak times — usually the morning rush in Brisbane or the evening cleanup in a Perth family house — and note the simultaneous flow rate. A typical ensuite with a 12 L/min shower, kitchen mixer and washing machine can demand 20 L/min, and a second bathroom can push that past 25 L/min.

Climate matters because cold inlet water forces the heat exchanger to work harder. Adelaide winter groundwater can sit around 12°C, while Hobart homes see 7°C. Manufacturers publish curves showing temperature rise at a given flow, so match those to your coldest expected input. LPG models behave differently from natural gas units and are common in regional South Australia and Tasmania, where reticulated mains gas is sparse.

Choosing the location and clearances

Tankless heaters are more forgiving than a 250-litre cylinder, yet the location still dictates the job. Many renovators tuck a unit into the laundry, but check clearances for combustible walls, the flue terminal and service access — usually 50–150 mm at the sides and at least 600 mm in front.

In a strata apartment in Sydney or Melbourne, body corporate rules often dictate where flue terminals can exit. Some inner Adelaide buildings have heritage overlays that limit visible flues. Thoughtful placement also keeps the appliance accessible to people who may struggle with heavy storage tanks, the same design instinct that informs contrasting stair treads.

Sizing the gas line for the new appliance

A 26 L/min continuous flow heater can draw up to 200 MJ/h of natural gas, more than double what an old cooktop and cylinder once consumed. The existing 20 mm copper line often needs upsizing to 25 mm or 32 mm, particularly in older fibro homes in inner Sydney and Brisbane where the original run loops through the roof space.

Your licensed fitter will calculate pressure drop across the meter, run length and total appliance load, including any new cooktop or BBQ bayonet. They'll add a sediment trap at the inlet to catch the scale and rust common in Australian mains, and a manual shut-off within reach of the unit.

Venting, flue and combustion air

The flue is the single most safety-critical part of the job. Sealed-combustion units use concentric PVC pressure-rated flue that draws combustion air from outside and expels products to the same terminal. The run must slope back toward the unit by at least 2°, follow the manufacturer's maximum length, and terminate clear of eaves, opening windows and dryer vents — usually 600 mm from a window and 300 mm from an adjacent wall.

Avoid running the flue through a tight ceiling cavity where it cannot be inspected, or discharging into a carport where family members sit during a Saturday BBQ. In bushfire-prone zones, including parts of the Adelaide Hills and the Blue Mountains, the terminal may need a spark arrestor. Where the home already has sustainable upgrades such as a green roof upgrade, similar care applies: keep flue paths away from planted areas damaged by warm exhaust.

Water connections, condensate and scale

High-efficiency units produce acidic condensate at roughly 1 litre per hour during heavy use, which must drain to a tundish and then to a sewer point or charged waste trap. In Brisbane apartments the laundry floor waste provides an easy outlet, but the condensate line must run inside the building and may need a small neutralising cartridge if local water is very soft.

On the water side, full-flow isolation valves on both hot and cold lines allow future descaling — a routine task in hard-water pockets around Perth and the Barossa. The installer should fit a service valve kit with a drain port and, for long pipe runs to the ensuite, a small circulation loop so taps reach temperature quickly without wasting litres. Compact units also suit secondary wet areas, and a small point-of-use model is one way to deliver instant hot water to a bar sink in projects such as creating a home bar with a built-in wine cooler and glass racks.

Electrical, controls and commissioning

The appliance still needs a 240 V power point for ignition, sensors and the modulating fan. The cable run should be RCD-protected and ideally on its own circuit so a nuisance trip doesn't black out the fridge. Smart controllers let owners pre-set a kitchen loop at 50°C and a bathroom loop at 60°C from the lounge, helpful during Adelaide winters when the family wants hot drinks the moment they walk in.

Commissioning covers leak testing the gas line with a manometer, checking flue draught with a smoke pencil, confirming condensate drains freely, and measuring outlet temperature against the setpoint at full flow. Your installer should record everything on the compliance certificate, walk you through the user controls, and label the gas and electrical isolation points so a future owner or emergency responder can shut the unit down in seconds.

Compliance, permits and long-term care

The certificate lodged with the gas distributor is your proof of compliance. In Victoria the plumber must register the appliance with Energy Safe Victoria; in NSW a Form 4 is lodged with the gas fitter's licence number; in Queensland and Western Australia the equivalent documentation goes to the state regulator. Keep the manual, warranty and commissioning record together — most brands require proof of professional installation for any future claim.

Service the unit every two to three years, or more often in hard-water areas: descale the heat exchanger, clean the inlet filter, vacuum the fan and check flue joints. With that routine, a quality gas continuous flow heater will deliver hot water for 15–20 years, outlasting a storage cylinder while shrinking the laundry's footprint.

The practical next step is to phone two or three licensed gas fitters in your state, ask each to quote against the performance specification you drafted earlier, and arrange a site visit before signing.