- The required size of a heat pump hot water system depends on how quickly the new system reheats water after use.
- Heat pump systems can efficiently heat water at any time of the day however some heat pumps are more powerful than others and can reheat water faster.
- Not all products will perform the same or deliver the same hot water output or efficiency.
- It is important to do your research on products to ensure they can perform efficiently and effectively in your location.
On this page:
What is an efficient hot water system and why should I install one?
Hot water systems account for around 18 per cent of energy use in Victorian households. Upgrading to an efficient hot water system is a great way for households to save on energy bills and reduce greenhouse gas emissions.
The Victorian Energy Upgrades (VEU) program offers incentives for households to upgrade to efficient hot water systems. Only products meeting the VEU program requirements can be installed under this program. There are two types of efficient hot water systems available under the VEU program:
- Heat pump hot water systems: Heat pump hot water systems include a heat pump unit and an insulated storage tank. The heat pump unit may be integrated on top of the tank, or it may be separate (split system) like the outdoor unit for an air-conditioner. The heat pump extracts heat from the surrounding air, which is used to heat water in the storage tank. These systems use around 60 to 75 per cent less electricity than a conventional electric hot water system.
- Electric boosted solar hot water systems: Solar hot water systems use heat directly from the sun to heat water in a storage tank. These systems generally include a hot water storage tank which is connected to solar collector panels. When the sun shines on the collector panel, the water inside becomes hot and is circulated to the storage tank.
For more information on how to organise a hot water system upgrade, visit hot water systems.
Product quality and warranty
There is a range of hot water systems eligible under the VEU program:
- Remember to do your research on these products. Not all products are of the same quality or suitability for all households.
- Using a trusted installer and buying a reputable brand and model will ensure your hot water system works as it should.
The performance and energy efficiency of hot water systems also varies between products:
- Choosing a more efficient system will deliver greater savings on household energy bills.
- For system specific information and enquiries, we recommend that you contact the manufacturer of the water heater.
It is important to consider warranty when installing a new hot water system:
- Not all hot water systems come with a warranty, and the warranties offered vary from one manufacturer to another.
- Remember to read the warranty conditions carefully and note that some warranties are conditional on installation by appropriately qualified personnel.
- A warranty is only as good as the company that provides it, so look for a company with experience in installing energy efficient hot water systems.
Choosing the right size hot water system
The size of a hot water system refers to how much hot water it can provide. This is determined by tank size (the amount of water stored, listed in litres) and how quickly new water entering the tank can be heated. Our recommendations rely on tank size because it is easily comparable.
Think carefully about what your household needs from a new system:
- a system that is too small for your household may mean regularly running out of hot water
- a system that is excessively large will cost more to buy and run.
Recommended tank size
Disclaimer: Sizing any hot water system should account for several factors and not only the number of bedrooms. We recommend that sizing and installation is always conducted by a fully qualified technician.
We recommend sizing your system based on the number of bedrooms, because the number of people in a household can change over the 10-15 year lifespan of a hot water system. For example, the demand for hot water might increase with the addition of children or tenants. The recommended sizes include some extra capacity to account for changes in water consumption and a range in the number of occupants.
These recommendations apply to both heat pump hot water systems and solar hot water systems. However, some solar hot water systems may benefit from larger tank sizes. It is important to discuss the particular sizing considerations of your chosen system with your installer.
Recommended tank size for water heaters
| Number of bedrooms | Recommended tank size |
|---|---|
| 1-2 | 150-225 litres |
| 3 | 225-300 litres |
| 4 or more | More than 300 litres |
How does household behaviour impact recommended tank size?
When and how frequently your household uses hot water will impact the size of the hot water system needed to meet your household’s needs.
It is also important to consider the water efficiency of your appliances such as:
- shower heads
- washing machines
- dishwashers.
Before investing in a larger water hot water system, consider upgrading the efficiency of your appliances. For example, efficient shower head upgrades are eligible under the VEU program and can reduce your water use and energy bills.
Consider a larger system than our recommended size if you have high hot water consumption. For example, if:
- there are multiple people per room in your house
- people in your house have long and/or frequent showers
- your household has inefficient showerheads
- people in your house shower directly after one another, or at the same time (in different showers)
- people in your house have regular baths
- your household has large spa baths or spas to fill
- your household has plumbed hot water for clothes washing machine and/or dishwashers.
Existing hot water systems
When looking at a replacement hot water system and estimating its size, consider using:
- your existing hot water system and water bills
- the size of the tank, if your current system has a storage tank
- your household hot water use and water bills, if your current system is instantaneous (without a storage tank).
Other considerations when planning a heat pump hot water system
When upgrading to an efficient hot water system, it is important to choose a reliable system that will last. A well-designed and efficient system will help to reduce energy bills and will serve your household for many years to come.
There are two types of heat pump hot water systems:
- Integrated systems: an integrated unit combines the heat pump components with tank in a single unit. An integrated system is more compact and has a simpler installation process.
- Split systems: in a split system, the heat pump component is housed in a separate unit, similar to a split system air-conditioner. A split system allows flexibility in locating the two components.
- Heat pumps primarily heat water using the heat from outside.
- Some heat pumps have an element to ‘boost’ hot water production using electricity. This can increase the speed that water is heated and can be useful in cold conditions.
- Electric elements increase energy use that will increase the running costs of the system. Therefore, you may wish to research products that can operate in colder conditions without the use of a booster element.
- Many heat pumps have a timer to control when water is heated to make the most of off-peak electricity prices and electricity generated from a solar photovoltaic (PV) system.
- Some heat pumps also include ‘smart’ functions to communicate with the solar PV system to optimises the use of solar electricity.
- If your household has solar or is on a time-of-use plan (e.g. peak and off-peak prices for your electricity bill) consider installing a heat pump that includes a timer, which may reduce your energy bills.
- A larger tank may be required for households using timers to reduce the risk of hot water running out between reheating times.
- Heat pumps generate noise comparable to an air-conditioner.
- Some heat pump systems are noisier than others.
- When installing a heat pump, it is important to select a location that is appropriate for you and your neighbours.
- Generally, heat pumps should not be installed close to bedrooms (outside a kitchen or bathroom might be more appropriate).
- Installing heat pumps near the bathroom or kitchen may also help to minimise heat loss from hot water pipes.
- It is important to do your research on models best suited to the climate of your location.
- All water pipes should be insulated to reduce heat loss and to minimise or eliminate frost damage.
- The energy use and performance of hot water systems is impacted by the local climate.
- It can take more energy and time to heat water in colder climates, reducing the efficiency and increasing the risk of running out of hot water.
- Some products may also rely more on the booster element as discussed above.
- Some systems also include ‘frost protection’ features to ensure they function effectively in cold conditions.
Other considerations when planning a solar hot water system
There are two common types of solar hot water systems: close-coupled systems (or thermosiphon systems) and pumped systems (or split systems).
Close-coupled systems have solar collector panels and a storage tank, which are all located together on the roof.These systems are simpler than pumped systems, require less maintenance, and also help to reduce heat loss through pipes because the components are located together. However, close-couple systems require a roof that can support the weight of the tank.
In pumped systems, the storage tank is located on the ground like a conventional hot water system. These systems use a pump to circulate water from the ground-mounted tank to the collectors on the roof. Pumped systems might be a suitable option if your roof cannot support the weight of the storage tank.
There are two common types of solar hot water collector panels: flat plate and evacuated tube.
Which type of collector you use depends on personal preference and your climate. In colder climates, evacuated tubes can be more efficient and tend to work better in cooler months. In warmer climates, either type of collector will perform well.
The number of collectors or tubes in the system will vary, depending on the local climate and the expected pattern of water use at home.
The required size of a solar hot water system also depends on how quickly the system reheats water after use.
Solar hot water systems usually can’t collect enough solar energy to heat the water during winter or if it’s cloudy, so they also use booster elements to heat water. The size and number of elements will impact how quickly your water can be heated.
Only electric-boosted solar hot water systems are eligible under the VEU program.
Solar hot water systems also offer frost protection systems, which can prevent damage to pipes in cold temperatures. Speak to your installer about models best suited to the climate of your location and whether frost protection is recommended.
Other considerations when upgrading from a solar hot water system with a non-functional solar component
Both electric and gas-boosted solar hot water heaters can often continue to provide hot water long after the solar component of the system has failed. As a result, the consumer will be unaware in most circumstances, unless they can isolate and understand what has caused the increase to their energy bills.
Under VEU, you can now also receive incentives to replace gas-boosted and electric-boosted solar water heaters. To be eligible, these systems must only provide hot water from electric or gas-booster, due to non-functional solar components that are no longer within the relevant warranty period, and at least 5 years has lapsed since the system was installed.
Note: electric or gas-boosted solar water heaters that cannot provide adequate hot water due to a non-functional electric or gas-booster are not eligible for incentives.
Why should you upgrade your non-functional solar water heater?
A non-functional solar water heater will continue to operate as a conventional and inefficient gas or electric water heater. These types of units are very expensive to run.
There can be other advantages to upgrading a solar water heater with an efficient heat pump water heater. The solar collector is usually orientated in the best location for solar input on the roof. This collector could then be removed from the roof and replaced with solar PV panels. These panels can then power the heat pump water heater, effectively providing hot water at almost no cost.
By removing a gas-boosted solar water heater, you may be able to electrify the rest of your household and disconnect from gas entirely. This means the annual gas network connection charges will be permanently avoided. This saves around $350 to $400 yearly on fixed network charges, in addition to much lower energy costs for your water heating.
Victorian Energy Upgrades provides further incentives to help you electrify your space heating and cooling and cooking.
What are common failures?
There are several ways that the solar component of the solar hot water system can fail:
- the pump on a pumped system can often fail, especially as the system gets older
- the temperature sensors may become dislodged or damaged
- the controller could develop a fault or not be programmed correctly
- components, valves or pipes may begin to leak or become blocked
- the collector could become damaged (e.g. from heavy hail)
- the tank may fail.
Note: It is not uncommon for pumps and controllers to be turned off, or for temperature sensors to be dislodged. These can be an easy fix.
How to check if your solar water heater has failed
We recommend asking a plumber experienced in determining these issues as it can be difficult to check, particularly for roof mounted systems.
One simple way you may notice if the solar component of your gas-boosted solar hot water system is non-functional is if the pressure temperature relief valve (PTR) no longer drips hot water on a warm sunny day.
You can check the hot water outlet from the tank or the hot water inlet from the solar system. If these are cold on a warm sunny day, there’s a good chance that the solar system is no longer functional. You can also try opening the pressure temperature relief valve, if the water that comes out of this valve is cold on a warm day, the system is likely non-functional. Test carefully as these can be dangerously hot.
To check systems that have the booster in the tank such as thermosyphon systems and systems mounted on a roof, you may be able to switch off the booster. If the tank does not reheat or even heat a little on a warm sunny day after exhausting all the hot water, it is likely non-functional. Be careful not to switch off pumps or controllers.
Check the manual for your product for more information. If you are uncertain, we recommend you contact a professional.
What to do if your solar water heater has failed?
Solar water heaters can still be very efficient and low cost to operate. If functional, your existing system could even be more affordable to operate than a new upgrade. You can find more information on the cost to run different types of systems on the following website: Compare water heating running costs | Sustainability Victoria
Depending on the type of failure, it may be more economical to repair the system. If the component that has failed is still under warranty, the system is not eligible for. Warranties can vary for different components, check the product manual specific to your model for more information. The product may also be covered by consumer guarantees under Australian consumer law. Reach out to the manufacturer or your installer of your water heater to resolve any faults that may be covered.
If the system is outside of warranty but is still young (5-10 years) or if the failure is an easy fix, a repair may be the most economic option. As the system becomes older, other components are likely to also fail in future meaning a more expensive repair may not be economic. We recommend getting independent advice from a qualified professional.
If your solar water heater only provides hot water from the electric or gas-booster, you may be able to upgrade to an efficient electric water heater at a discounted price through the VEU program. For more information on upgrading your water heater through VEU, visit the following page: Hot water systems for households.
Page last updated: 23/10/24