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How does an instant gas hot water system work?

What is an instant gas hot water system?

Instant gas hot water systems, otherwise known as tankless, instantaneous or continuous flow, only heats water as and when you need it. This reduces the amount of water wasted during the lag time for hot water to reach the tap, making them a great option for all kinds of homes and businesses.

How does an instant gas hot water system work?

Continuous flow hot water systems work by heating water as needed, with either a pilot flame or electronic ignition (which can be placed both internally and externally, but only if sufficient ventilation is an option). Water is heated by a gas burner as it flows through a coiled pipe, which is known as a heat exchanger. When a hot water tap is turned on, the gas burner starts, only heating the amount of water that is required. This offers a range of benefits, as it does not continuously keep heating a full tank of stored water. This means that there is no heat loss from a tank, resulting in both energy and cost savings.

To ensure the water is heated correctly, the pace of the water is slowed down as it flows through the heat exchanger. This means that instant gas hot water systems supply hot water at a lower pressure than storage systems.

Instant gas hot water systems typically deliver hot water at flow rates per minute of between 10 litres and 30 litres, depending on the model.
Instantaneous Gas Hot Water System.*

What are the installation requirements for an instant gas HWS?

In order for you to have an instant gas hot water system you must have a gas connection - whether this is installed already, or requires installation. You must also have an adequate place to put the hot water system - whether indoors with good ventilation via a flue or outdoors. If you are unsure, give your local hot water specialist a call (or call us!).

What are the pros and cons of an instant gas hot water system?


  • Highly efficient and energy saving.
  • Reduce wasted water.
  • Small, so can fit almost anywhere.
  • Reduce lag time for hot water to reach the tap.
  • Can be installed almost anywhere - indoors and outdoors.
  • Both flued and unflued options.
  • Can be used as an energy efficient backup booster for solar hot water systems.
  • In theory, never run out of hot water again (if system is the correct size).


  • Expensive upfront costs, especially if you have to have a gas connection installed.
  • If gas isn't available in your area, this isn't an option - unless you are looking to use LPG.
  • LPG can be expensive.
  • A continuous flow of gas is required to deliver continuous hot water, therefore you must ensure you have appropriately sized gas pipes and gas meters to service the system.

Who does an instant gas hot water system suit?

An instant gas hot water system is great option for a range of homes of up to four people, as long as they are connected to gas (or are prepared to pay higher costs for LPG). Installing multiple units may be needed for large homes or buildings.

Brisbane Plumbing and Drainage

If you would like further information in relation to installing a gas hot water system in your home or workplace, give Brisbane Plumbing and Drainage a call today on {{ context.constants.company_info | parse_json | dig: 'secondary_phone' }} and we can assist.

Need some more help?

Learn more about how hot water systems work here, or head to one of our specific information pages below:



Australian Government - Your Home :

Department of the Environment and Energy (Energy Basics) :

Department of the Environment and Energy (Hot Water Systems) :

Canstar :

Sustainability Victoria :

*Photo courtesy of BUILD.


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