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Hot Water Units

If you are trying to find the best hot water system for your new house it can be pretty confusing. Set out below are descriptions of the types of hot water heaters currently available on the market and how you can best take advantage of the abundant sunshine and warm weather we have in WA for heating your water.


Your Builder will have a standard hot water unit that they install as part of your home package. Its a good idea to check what it is. Previously the standard was nearly always a gas storage hot water unit. However with Government rebates available more environmentally friendly options are becoming more common. Solar or heat pumps use less energy than most, alternatively gas or electric instantaneous can be a viable option. Remember check the star rating........The more stars the better. The Government phased out greenhouse intensive Hot Water Units (electric storage) during 2010-2012. 


The other issue with hot water units is position of the system. The distance the water needs to travel from the unit to the tap can have a direct effect on both your water bill and your gas/electricity bill. If you need to let 2 litres of water go down the drain before the hot water arrives in the kitchen there is a serious position problem. Normally the hot water unit is placed closest to the kitchen as this is where the hot water is used most often. However if your ensuite and bathroom are upstairs on the other side of the house all the savings of having the most cost effective, environmentally friendly hot water unit will literally be washed down the drain with your excess water bill. You might want to consider 2 smaller units in this instance rather than one large unit. Or you could install a something like Autocirc to reduce water wastage.

Ways to heat your Water

  • Solar- most environmentally friendly option, preferably with gas booster
  • Gas- less green house emissions than electricity, storage units do keep all the water hot ALL the time not just as you need it.
  • Electric- instantaneous heats the water only as you need it. 
  • Heat pumps- newer product- environmentally responsible

Types of Hot Water Units

  • Solar with gas or electric booster
  • Storage hot water, gas or electric
  • Continuous flow (instantaneous gas or electric)
  • Heat Pump

Consider your needs and how many people are at your house:

  • Small Household- instantaneous system or effective small gas storage system
  • Medium Household- If your climate permits solar, heat pump or a high efficiency gas system
  • Large Household- Solar, high efficiency gas storage system or solar boosted heat pump
  • Up to 20% of household emissions are created by hot water usage. Hot water creation can represent up to 50% of household utility costs.


The normal allowance of water usage for a household is up to 50 litres per person. Depending on the speed of recovery, this will dictate the size of tank you require. (not applicable to instantaneous)
Check the energy star rating on any system you are considering…….the more stars the better, some units have nearly 7 stars.
Thermostats for fueled systems are normally set at about 65-70 degrees, if you reduce the thermostat by 5 degrees you it is unlikely you will even notice the different but your bills will be reduced.


Gas is a relatively inexpensive and environmentally responsible natural resource. Gas HWU’s come in two types, gas storage and gas instantaneous. All gas storage units in WA must be 5 star energy rated or higher. Nearly all gas HWU’s must be installed OUTSIDE and at a distance of 1meter away from opening windows. However some units can be mounted inside cupboards or in the roof space if required


Production of electricity is one of the largest contributors to pollution  on the planet. Manufacturers of electrical appliances are now striving to create appliances that use less and less electricity, and the electricity that they do use is being utilised much more efficiently than in previous times. Items that waste electricity like electric storage hot water units are have been phased out with more friendly options like 'on demand' electric hot water units (also known as Instantaneous or Continuous Flow)

Continuous Flow / Instantaneous Systems or On Demand Hot Water Systems

This type of unit has the great advantage of the water only being heated as you need it. You don't waste money heating water that you're not using and you won't run out of hot water as there's no tank. Your unit can have a gas ignition (this ignition will cost more to run as the pilot light needs to stay lit) or an electronic ignition system which uses no energy at all when not in use, but be aware your hot water unit will not work during a power failure. Check water pressure available on the unit before you buy and also confirm your low flow shower heads are compatible with the flow rate. Units are wall mounted and great where space is at a premium.

Gas Instantaneous 

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Instantaneous gas HWU’s are small wall mounted units that heat the water as required, therefore saving on the gas bill from a storage unit. Some units deliver poor water pressure. Gas instantaneous units are now available with touch pads for the bathrooms so you can pre-set the water temperature (a great safety feature) to avoid scalding. Kitchens and Laundry’s can be set to a higher temp’s. Water saver features are also available

Electric Instantaneous   

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Much lower running costs than electric storage . Units are slimline and wall mounted so good for situations where space is limited. Three phase power is required. Remember if there is a power failure you will have no hot water. These units are fabulous if you want to install two systems because your ensuite is miles away from your kitchen. Features are similar to Gas Instantaneous with touch pads and thermostatic controllers.

Storage Hot Water

The water is heated and stored hot in an insulated tank in the unit until you use is. As you use hot water cold water is added into the tank, the burner or element then turns on which reheats the entire tank to the temperature set on the thermostat. Normally water pressure is pretty good with these systems. Tank takes up a bit of room. Gas storage usually reheat water faster than electric storage units, thus the tank can be smaller. If you insulate the first 2 metres of pipes from the HWU and the pipe from the relief valve this will reduce heat loss even when the unit is not being used. Insulating all the pipes is not normally cost effective. You can also wrap your storage tank in an insulating material i.e. silver foil roof insulation. Pipe insulation is available from plumbing suppliers or hardware store. You will save substantially on your utility bill by doing this.

Gas Storage   

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Gas storage used to be the most common type of unit used by Builders. It is inexpensive to buy, but the rather expensive comparatively to run. The gas comes on to heat the tank when ever the water temperature falls below a pre programmed temperature. Hint: If you are on LPG tanks don’t specify this option as you will be forever refilling your tanks. These units generally supply great water pressure and are OK if using 2 hot taps at once. There is now a movement away from these units towards Solar Units and Heat Pumps, this is due to the generous government rebates currently available. Gas storage units in WA must be 5 star rated or higher. This means the only units available in WA are highly efficient.

Electric Storage

These units were phased out in  2012 due to a Government Initiative. It is against regulation to install then into a NEW home.


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Living in Australia solar hot water is a fantastic idea. Although more expensive initially to purchase and install most units have paid for themselves within 5 years. Flat solar panels are placed on roof and a hot water tank is located either on the roof adjoining the panels or at the side of the house (more expensive). The sun then heats the water for free and you use it. On days when there is no sun, the booster can be turned on. The booster can be either gas or electric. Gas boosted solar hot water systems are the most environmentally friendly hot water option currently available. Gas is cheaper to use but more expensive to install, electric is cheaper to install but more expensive to use. Solar hot water units must be place on the North face slope of the roof. Some top of the range units have an automatic booster which turns its self on when the water drops below a certain temperature.
The only down side being if there’s no sunshine and you haven't turned the manual booster on you might be waiting a while for your shower.
Hint: Install a timer on your booster so you don’t forget to turn it off. Or so you can set it to turn on at 5am for an hour on winter mornings.
Substantial Government rebates are available but they end on 31 June 2013  

Heat pumps   

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These units are like a storage hot water unit but work in the opposite way that your fridge works. (they plug in just like a fridge as well) They draw latent energy for the surrounding environment and use it to heat your water.  These units are environmentally responsible (using approximately 70% less power than an electric storage unit). Most units will deliver mains pressure at a couple of taps at the same time, however this will depend on the water pressure at your house. Its a good idea to check at what temperature your heat pump stops working. This can range from 5 degrees to minus 10 degrees. If your unit stops functioning at 5 degree and you live in an area where it gets that cold at night choose one with an electric booster that will kick in automatically if the exterior temperature gets below about 5 degrees this will ensure constant hot water delivery. Heap pumps work really well in warm environments like Perth. Currently generous government rebates are available on these units.

Helpful Hints

If you are considering a solar HWU and live in a frost prone area you will need a unit suitable for frost exposure.
Always locate your HWU as close to the wet areas as possible. It may be useful to consider 2x units if your bathrooms are far apart.
Water pressure, do you want to run 2 taps at once?
Consider installing a water saving device like an  Enviro Save Water System as seen on the New Inventors

Related Topics

Water tanks
Solar passive design
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