What you think you see is not always what you get. That's the sad fact being faced by some water heater buyers. They look forward to the treat of a shower with plenty of steady, strong water pressure - only to find the stream of hot water turning into a trickle when more than one tap is turned on! It's easy to understand their disappointment, especially after they thought they had installed a 'state of the art' water heating system. When it's time to install a water heater, either for a new home or to replace an existing unit, there are two basic types available.
Types of Hot Water Heaters
Mains Pressure
Firstly the Mains Pressure type, where water is heated and then kept hot in a super-insulated storage cylinder. There are several advantages to this type of system. The most obvious is the ability to supply large amounts of hot water on demand to more than one tap, at the same time.
Continuous Flow
The other choices for the water heater consumer go under the names of 'instantaneous', 'continuous flow', 'single tap', 'electric coil' or 'gravity feed' models. The basic design of this type of water heater goes back to the 1890s and currently all of the instantaneous units available in the market are imported from other countries where peoples' hot water requirements are considerably different to ours in Australia!
Pros and Cons
One of their limiting features, compared to mains pressure styles, is that 'instantaneous' and 'coil' water heaters cannot deliver hot water to your shower at mains pressure. They have to reduce the mains pressure flow of water so it can be heated. Result? When another hot water tap is turned on your shower may turn to a trickle. You may need to be prepared to buy two or more water heaters for your home, one for each end of the house.
Instantaneous water heaters have limited their popularity to places like caravans, granny flats and studio apartments - where there is usually just a single person.
There may also be a hidden trap for purchasers of the larger instantaneous models. Instantaneous water heaters' major characteristic is that they restrict the flow of water so it can be heated. The water is heated in a heat exchanger every time the hot water tap is turned on. This process results in 'start up losses'. The heat exchanger must heat and reheat so it can transfer the energy to the cold water. This may mean wasting energy and water, every time. How many times each day are the hot water taps in your home turned home? Anyone considering the purchase of an instantaneous water heater should first check whether the gas supply is adequate, as running in larger gas lines can be very costly.
Mains pressure water heaters, such as those from well known names such as Rheem and Vulcan, deliver a steady, strong stream of hot water to more than one tap at the same time... and a bath, or dishwasher or second shower. Only mains pressure water heaters can take advantage of offpeak electric heating and solar assist, which can help you save up to 50% or more of your annual water heating fuel costs. They don't need any separate temperature control panels and they are much more simple to install and use.
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