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A popular system
The electrically heated storage cylinder is the most common water heating system in Tasmania. The most common size sold in Tasmania is the 160L. It is estimated that between 800 and 1000 hot water cylinders are replaced each month in Tasmania.
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How do they work?
Storage cylinders are made of stainless steel, copper or mild steel coated with vitreous enamel. Long-life glass-lined mild steel cylinders, generally have warranties of 10 years. The more common and shorter life storage cylinders generally have five year warranties.
Common storage heaters are made up of an insulated tank containing a heating element at the bottom. Cold water flows in near the bottom of the tank and leaves the tank as hot water through an outlet near the top of the tank. A thermostat is located on the tank and the minimum temperature this is set at is 60ºC. This minimum temperature is for health and safety reasons. Conversely, setting the temperature too high (and 80ºC can be quite common) wastes large amounts of energy and is unnecessary.
As hot water flows out of the tank it will pass through a ‘safety valve’ which serves as a pressure relief valve. If this valve is dripping or making a hissing noise, contact your licensed plumber immediately. These symptoms could indicate excessive tempratures within the valve, or a faulty valve.
Hot water heaters also contain a vacuum break. A little further down the outlet pipe on a newly installed tank will be a tempering valve which adds cold water to the hot water to be delivered to outlets in the bathroom. Water coming out of the tap is required to be 45ºC for safety reasons.
The tank will also contain what is known as a sacrificial anode which acts to reduce the corrosive effect of electrolysis in the tank. There are different types of anodes available and which one is appropriate will depend on the hardness of your water (how much calcium carbonate [CaCO3] it contains).
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What options exist?
Not all cylinders will be the same. Some of the available options include:
- Long-life cylinders or ‘standard’ life cylinders
- Heat exchange systems
- Low pressure systems
Heat exchange systems
Water storage cylinders using the heat exchange concept pass water through a copper coil immersed in hot water inside the insulated copper tank. The hot water in the tank warms the cold water in the copper tubing. They are not open vented (meaning they do not lose water through the expansion pressure relief valve found on other tanks). They do not contain sacrificial anodes. Note that these systems can be used with mains pressure. To ensure maximum operating efficiency, the pressure relief topping-up valve will need to be activated every six months.
Low pressure systems
It should be noted that the use of a stainless steel or low pressure hot water system can prolong the life of the system, lasting 25-30 years. Low pressure systems cannot be installed in houses where the appliances and fixtures are only suitable for high pressure, e.g. mixing taps, some shower heads.
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What to consider when choosing a new hot water heater
Sizing
In many cases the tanks are oversized to avoid running out of hot water. This over-sizing wastes energy and can also be very expensive to run. Think about the number of people in the house, number of bathrooms and fixtures, the use of appliances, and very importantly, consider your lifestyle eg. a household with four sports active children could require 10 showers a day. This could amount to 1000 litres of 40°C water per day.
Under-sizing is also inefficient and, when choosing a hot water system, householders should also consider changes likely to occur within the life-time of the system – eg. family additions, the advent of adolescence, children leaving home and its impact on hot water consumption.
The following sizing guide is based on manufacturers recommendations, adjusted to suit Tasmania’s continuous hot water electricity rate.
Sizing guide – electric storage systems
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Number of People in Home
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Continuous Electric
Tariff 41
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OffPeak Tariff
Electric Tariff 61
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Capacity
Litres
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Element
Size kW
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1 and 2
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80
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1.8
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2 and 3
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125
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1.8
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4 – 6
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1 – 3
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160
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2.4
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5 – 8
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2 – 4
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250
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3.6
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6 – 10
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3 – 6
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315
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4.8
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8 – 13
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5 – 8
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400
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4.8
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NOTE: When connecting your hot water heater to an OffPeak tariff, you may need to purchase one that is larger than your existing unit.
Location of hotwater cylinder
Ideally a cylinder should be as close as possible to plumbing fixtures within the house. It must also be readily accessible. In some cases, it may actually be better to install a second hot water system, eg. where there is an ensuite at the opposite end of the house to all the other fixtures.
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Maintenance
Steel mains pressure systems will last longer if the sacrificial anodes are changed regularly.
Mains pressure temperature and pressure relief (TPR) valves have a life of about five years and need to be checked regularly for correct operation. Water should only drip from the TPR valve when the element is on. Continuous dribbling or a flow of water from this pipe is an indication something is wrong and it is time to call a plumber or a GreenCity Service TM provider (please see below).
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Next steps
Installation and maintenance of a hot water heater should only be carried out by a professional plumber. You can contact the Master Plumbers Association of Tasmania on 1800 667 766 for further advice.
If you are interested in a home water audit, general advice about water efficiency or energy efficiency in relation to a hot water system you should contact the Master Plumbers Association of Tasmania on 1800 667 766 who can direct you to your nearest GreenCity Service TM provider.
The GreenCity Service TM is an environmental program based on the long-term goal of improving the sustainable use of our valuable resources. It aims to nurture close co-operation between municipalities, industry and the public. Issues addressed include: water efficiency around the home; appropriate selection of a hot water system for a home and how to improve the operating efficiency of a currently installed hot water system.
(This information was kindly supplied by the Master Plumbers Asssociation, 2004)
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