Sustaining our environment

Choosing a hot water system

Types of hot water systems

Water heating is the biggest energy user in NSW homes. Electric hot water systems typically account for more than a third of household energy use. Because most electricity in NSW is generated from coal-fired power stations, electric hot water systems emit the most greenhouse gas emissions.

Solar

  • A solar hot water system, which may cost more than a conventional hot water system, can substantially reduce your power bills by lowering the energy cost of heating hot water.
  • In NSW, approximately 65-80% of your hot water will be free of charge
  • All systems come with a gas, off-peak electric or solid fuel booster to supply hot water during periods of low sunshine.
  • Collector panels are located on the roof, with a storage tank either on the roof or at ground level.
  • Solar hot water systems have a low impact on the environment.

Heat pumps

  • Highly efficient form of water heating which uses around 70% less electricity than other electric water heaters.
  • When used in conjunction with a timer and the off-peak tariff, running costs are even lower.
  • Heat is extracted from the atmosphere using a refrigerant gas and a compressor (much the same way as heat is extracted from your refrigerator) and used to heat water stored in a tank at ground level.

Natural gas

  • Both storage and continuous flow systems are available.
  • Look for the energy rating label with the highest number of stars - choose one with a 5 or 6 star energy rating. 
  • Internal and external models available.

LPG

  • Running costs average around one and a half to three times the price of natural gas or off-peak electricity.
  • Look for the energy rating label with the highest number of stars.
  • Storage and continuous flow units are available.

Solid fuels (wood, briquettes, coal etc.)

  • Cost of fuels varies greatly.
  • Can be used alone, or in conjunction with off-peak electricity and/or solar in constant pressure storage units. 
  • Water can be heated using a 'wetback' attached to a slow combustion wood heater, or a stand-alone water heater powered by solid fuel.
  • Must not be used with mains pressure systems, unless a heat exchanger is used.
  • Not available for continuous flow systems.

Off-peak electric

  • Can only be used in storage systems of 160 litres capacity or greater.
  • Water is heated overnight to provide adequate hot water during the day.
  • Twin element units can operate with a 24-hour off-peak boost (if hot water runs out, water is reheated automatically on the off-peak tariff). Check with your electricity supplier for more information. 
  • Internal and external models available.

Peak electric

  • Used for electric continuous flow units, storage water heaters with a capacity of less than 160 litres and heat pump type storage systems.
  • With the exception of heat pumps, these systems can be very expensive to run, so should only be used when other options are not suitable.

Storage compared to instantaneous water heaters

There are two different types of gas hot water systems: storage water heaters and continuous flow (instantaneous) water heaters.

Continuous flow (instantaneous) water heaters heat water as it is required, therefore cannot run out of hot water. They operate most economically on natural gas. These systems are more suitable for smaller households with lower hot water usage, as they heat only what is needed, and don't waste energy heating up and storing water that isn't used.

Storage systems heat water and store it in the tank for use throughout the day. These are suitable for households with higher hot water usage. Storage water heaters heat and store water in an insulated tank ready for use. They operate most economically on solar energy, natural gas or off-peak electricity.

To decide which system is best suited to your household have a look at the tables below and calculate purchase and installation price, the unit's efficiency and running costs, and the life expectancy of the unit.

What size should I choose?

Note: High water usage households (eg those with spas or dishwashers) should select the next largest system size in the range. A dishwasher with a hotwater connection should be counted as an extra person.

The following tables are a guide only and you should consult your supplier for specific recommendations.

Electric storage water heaters (including heat pump)

Off Peak*

Peak rate

Max no. of persons served

Capacity (litres)

Max no. of persons served

Capacity (litres)

3

160

2

40

4

250

3

63

6

315

4

80

8

400

5

125

*high volume water users (eg where spas or dishwashers are used) should select the next largest system size in the range

Gas water heaters

Storage

Continuous flow

Max no. of persons served

Capacity (litres)

Max no. of outlets served
at one time**

Flow rate (litres
per minute)

3

90

1

16

4

130

2

20

5

170

3+

24

6

200

-

-

9

260

-

-

** Continuous flow systems are sized according to the required flow rate. A guide is often the number of bathrooms in the home. Consult suppliers of manufacturers for specific sizing guidelines for their products.

Solar water heaters

No. of persons served

Capacity (litres)

Collector (m2)

1-2

160-200

2

3-4

300-370

4

5-6

440

6



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Page last updated: 12 February 2014