Gas hot water systems burn either natural gas (also called mains gas or reticulated gas) delivered via a piped network, or LPG (liquefied petroleum gas), which is usually bottled.
There are two types of gas hot water systems, or gas water heaters:
- storage systems that store water in a tank
- instantaneous (or continuous) systems that heat water as it is used.
Gas hot water heaters produce from 25 to 33 per cent of the greenhouse gas emissions compared with electric storage hot water heaters.
How do gas hot water systems work?
Storage heaters
Storage heaters use a gas burner located under the storage tank to heat the water. They usually have a pilot flame that burns continuously and lights the main burner when it’s needed. Storage systems lose heat through the walls of the tank so they need to burn gas regularly to keep the water at the desired temperature. These losses can be a significant part of your hot water energy use. Well-insulated tanks will have lower storage losses.
Storage systems should be set to at least 60°C to kill dangerous germs.
Systems installed indoors need a flue that leads outside to vent exhaust gas.
Instantaneous heaters
In an instantaneous system (or continuous flow system) there is no storage tank and the water is heated as required. They don’t have heat losses from a tank.
The water is heated by a gas burner as it flows through a coiled pipe called a heat exchanger. The gas burner starts when a hot water tap is turned on. It only heats the amount of water that is required instead of continuously heating a full tank.
Is gas hot water right for you?
Whether a gas water heater is the best choice for you depends on your particular circumstances.
If you have access to both natural gas and sunshine, you could consider a gas-boosted solar system to reduce your energy use and greenhouse gas emissions. Gas water heaters generate far fewer greenhouse gas emissions than electric storage systems.
Getting the most out of a gas hot water system
All gas hot water systems except gas-boosted solar systems have an energy star label - similar to the energy label on electrical appliances - to tell you how efficient they are. To compare the energy use of gas storage and instantaneous gas water heaters, check the star rating label. The more stars, the less gas used and the lower the operating costs. This also means reduced greenhouse gas emissions.
