Wednesday, October 28, 2009

Choosing a Hot Water System

Types of hot water systems

Water heating is the biggest energy user in your home. When choosing your hot water system, many factors need to be considered, eg: the initial cost, on-going running cost, life expectancy and environmental impact.

Traditional electric hot water systems typically account for more than a third of household energy use. Because most electricity in Australia is generated from coal-fired power stations, electric hot water systems emit the most greenhouse gas emissions.

You must also choose between storage water heaters and continuous flow (instantaneous) water heaters.

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.

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.

Off-peak Electric
Running costs similar to natural gas.  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).  Note: not all states of Australia allow electric hws to be installed into new homes.

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.

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.

A solar hot water system, which requires an additional investment of $1,500-$2,000 above the price of a conventional hot water, can pay back the additional cost in energy savings in approximately 5-10 years.  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 the lowest 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.

How much hot water storage do I need?
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.

Electric & heat pump storage water heaters
1-3 people  160 litres
2-4 people  250 litres
3-6 people  315 litres
5-8 people  400 litres

Gas storage water heaters
1-3 people    90 litres
2-4 people  130 litres
3-5 people  170 litres
4-6 people  200 litres
5-9 people  260 litres

Solar storage water heaters
1-2 people  160-200 litres
3-4 people  300-370 litres
5-6 people  440 litres

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.

What are the cost differences?

Below are indicative pricing for supply & installation of hot water systems.  The federal government is currently offering rebates for solar & heat pump installations.  Visit to see if you are eligible.
Electric      $   800 - $1,500
Heat Pump  $2,500 - $3,500
Gas/LPG     $   800 - $1,200 (storage)
Gas/LPG     $   800 - $2,100 (continuous)
Solar         $2,500 - $4,500