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Hot water is one of those things you do not think about until it stops working. Most Australians have a hot water system in their home that will last 10 to 15 years with proper maintenance, but very few people know how their system actually works or what the differences are between the main types. That knowledge matters when you are comparing options, planning a renovation, or facing an unexpected replacement.
The Basic Principle
All hot water systems do the same fundamental job: they heat cold water from the main supply and deliver it to your taps, showers, and appliances at a usable temperature. Where they differ is in how they heat that water and whether they store it or heat it on demand.
Electric Storage Systems
Electric storage hot water systems are one of the most common types found in older Sydney homes. A cylindrical tank, typically located outside or in a garage or laundry, holds a stored volume of water (usually between 125 and 400 litres) and keeps it at a set temperature using an electric heating element inside the tank.
When you use hot water, cold water enters the bottom of the tank as hot water is drawn from the top. The element then heats the incoming cold water to bring the tank back up to temperature.
The advantage of electric storage is simplicity. There are few mechanical components, they are relatively inexpensive to purchase and install, and they are straightforward to repair. The main disadvantage is running cost. Heating a full tank of water continuously and keeping it at temperature around the clock is energy-intensive. Off-peak tariffs can reduce this cost significantly, but the system needs to be set up to take advantage of overnight rates.
Electric storage systems are generally not the most energy-efficient choice for new installations, but they are a reliable option and widely available.
Gas Storage Systems
Gas storage systems work on the same principle as electric storage: a tank holds a volume of water kept at temperature. The difference is that a gas burner at the base of the tank provides the heat rather than an electric element.
Gas heats water faster than electricity, which means gas storage systems tend to have a shorter recovery time after the stored hot water is depleted. They also generally have lower running costs than electric storage, depending on gas tariffs in your area.
Gas storage units require a natural gas or LPG connection. In Sydney, natural gas is available to most established suburbs, but coverage in outer areas varies. LPG is an option for homes without gas connection, but the ongoing fuel cost is higher.
Gas Continuous Flow (Instantaneous)
Gas continuous flow systems, sometimes called instantaneous or on-demand hot water, do not store water at all. Instead, when you open a hot tap, cold water flows through a heat exchanger inside the unit, and a gas burner heats it instantly as it passes through.
The main advantage is that you can never run out of hot water. The unit heats on demand, so as long as the gas supply is active and the unit is functioning, hot water is available indefinitely. This makes continuous flow systems particularly well-suited to larger households with high hot water demand.
Running costs are generally lower than storage systems because you are only heating water when you actually need it. There is no standing heat loss from a stored tank.
The trade-off is a higher upfront cost compared to storage systems, and the flow rate at the outlet needs to match the capacity of the unit. If multiple outlets are running simultaneously in a large home, a higher-capacity unit is required.
Heat Pump Hot Water Systems
Heat pumps are growing in popularity across Sydney as energy costs rise and households look for more efficient alternatives. A heat pump hot water system works like a reverse air conditioner: it extracts heat energy from the ambient air and uses it to heat water stored in a tank, rather than generating heat directly from electricity.
Because the system is moving heat rather than generating it, a heat pump typically uses around 60 to 70 percent less electricity than a conventional electric storage system. The running cost savings over a year can be substantial.
Heat pumps work best in climates where the ambient air temperature stays above around 5 degrees Celsius, which describes Sydney’s climate well for most of the year. They require adequate outdoor space and some clearance for airflow, and they produce a low level of noise during operation, which is worth considering for placement.
Solar Hot Water Systems
Solar hot water systems use solar collector panels, typically installed on the roof, to capture energy from sunlight and transfer it to a storage tank. In Sydney, with its high number of sunny days per year, solar hot water can dramatically reduce the energy cost of heating water.
Most solar systems include a gas or electric booster that activates automatically on cloudy days or during periods of high demand to ensure you always have hot water available.
The upfront cost of solar installation is higher than other system types, but federal government rebates and the ongoing running cost savings mean that payback periods are often competitive over the life of the system.
Choosing the Right System
The right system depends on your household size, your existing connections (gas or electricity), your roof space if solar is a consideration, your budget for upfront installation versus ongoing running costs, and whether the home is a new build or an existing property.
A licensed plumber can assess your home and recommend the most appropriate option. In NSW, any installation of a hot water system must be carried out by a licensed plumber. Incorrect installation can affect efficiency, safety, and the validity of manufacturer warranties.
If your current system is more than ten years old, it is worth having it assessed. An older unit operating at reduced efficiency can cost significantly more to run than a modern replacement, and getting ahead of a failure is far preferable to an emergency replacement.
