Electric hot water systems are by far the most common sort of hot water heaters in the Australian home. They have been made here in Australia for over 100 years,.  The technology hasn’t changed much over this time, just different materials are used and with thicker and denser insulation around the storage cylinders, this holds the temperature within for longer periods of time,  therefore having less heat loss equals slightly better efficiency from electric hot water systems manufactured prior to 2000.

Working the same as a kettle with a heating element, they come in 3 different power ratings for the Queensland market, 1.8kw, 2.4kw and 3.6 kw (some areas have 4.8kw elements but few and far between in Queensland due to the draw of power required). This is the same throughout all brands like Rheem, Dux, Vulcan, AquaMAX, Rinnai electric  hot water systems 

Having different size elements does not equal different energy ratings, for example a hot water heater with a 1.8kw element (1800 watts) will use half the power as a 3.6kw (3600 watt) element but will take twice as long to heat the same body of water to the same temperature.

Electric hot water system are manufactured out of mild steel tanks that is vitreous enamel lined internally and protected by a sacrificial anode and stainless steel, They old copper style water heaters are no longer available

An electric hot water system generally will equate to at least 1/3 of your power bill when you don’t have P.V solar usage and sent back to the grid for a buy back price on your tariff 11, which is what your general power and lighting are connected to, to supply power 24 hours a day at a cost higher rate. Your P.V solar power, should you have it will not help or power a hot water heater when it is connected to tariff 33 which is an 18 hours a day power guarantee and normally will be on expect for 6pm to 9pm and 6am to 9am or tariff 31 which provides power only during the lowest draws on the electrical grid and generally is between 9pm and 6am.

Tariff 31 will not provide enough power for hot water cylinders below the size of 250 litre when for 2 or more people

Electric hot water systems come in tank sizes that range from 25 litres that is used for kitchens and single sink applications right through to 400 litres

Below is a approximate person to size recommendation.

There may be slight variations due to the amount of hot water used by occupants

50 litres & 80 litres = 1-2 people in a unit type home and only connected to tariff 11 and can not be connected to a off peak tariff to provide reliable hot water

125 litres = 2-3 people in a unit or small town house, when connected to tariff 33

160 litre = 2-4 people in a unit or small town house, when connected to tariff 33

250 litre = 2-4 people when connected to tariff 31 and is what is in most 3 bedroom homes built and up to 6 persons when connected to tariff 33

315 litre = 3-5 people when it is connected to tariff 31 and up to 7 persons on tariff 33

400 litre = 4-7 people when connected to tariff 31 and up to 9 people when it is connected to tariff 33 and 12 people on tariff 11