Choosing the right hot water system for your home is not about guessing. Research from ScienceDirect shows that water heating accounts for roughly 26% to 30% of household energy use. A correctly sized system improves energy efficiency, gives consistent hot water, and helps manage bills.
Sizing your system means balancing the amount of hot water your household uses each day with the capacity of the storage tank and the type of water heater you choose. Getting this right ensures your system heats water effectively without wasting energy or running out of hot water at the worst time.
Understanding System Sizing
System sizing is the process of matching your household’s water usage with the right hot water system size. Every home is different, and your family’s daily hot water usage will determine what size hot water system suits you best.
An undersized water heater can struggle to meet demand, while an oversized system may waste energy keeping unnecessary water hot. The key is balance.
You’ll need to consider:
- Household size and water fixtures that draw hot water
- Water heating method such as solar, heat pump, or electric
- Storage system capacity or continuous flow rate
- Incoming cold water temperature and desired hot water temperature
- Flow rate of outlets like showers or taps
Getting the right size ensures consistent water temperature, faster hot water recovery, and better overall energy efficiency.
How Household Size Affects Hot Water Demand
Your household size is the most important factor in determining system capacity. Each person typically needs between 50 and 70 litres of hot water per day, depending on lifestyle and water use.
As a general guide:
- One to two people typically need a 150–200 litre storage water heater
- Three to four people usually need a 250–300 litre tank size
- Five or more people may need 400 litres or more, or a larger system with additional collectors
If you often use multiple hot water outlets at the same time, such as two showers or a dishwasher and washing machine, your daily hot water usage will increase. Matching your system size to your household’s hot water needs ensures you never run out of hot water during peak times.
Storage vs Continuous Flow Systems
There are two main categories of hot water systems available in Australia: storage systems and continuous flow systems.
Storage systems use a tank to store and heat water in advance. The system heats water and keeps it at a set temperature until you use it. Storage tanks are common in electric water heaters, gas storage systems, and solar water heaters.
Continuous flow systems heat water on demand as it passes through the unit. These systems are also called instantaneous or gas continuous flow units. They do not store water, which saves space and energy.
Your choice between a storage tank or a continuous flow system depends on how much hot water your household uses and how many hot water outlets operate at once.
Choosing the Right Tank Size
Choosing the right storage tank size ensures a steady supply of hot water without wasting energy. The tank must store enough hot water for your household’s typical usage.
Consider:
- Water usage patterns throughout the day
- Number of people in the home and how many water appliances you use
- Type of heating system (solar, gas, or electric)
- Collector area in solar systems that determines heat collection
- Incoming water temperature which affects how fast your system heats water
For example, a four-person home with average water use might need a 300 litre electric storage water heater or a similar-sized solar hot water system with two solar collectors. A correctly sized storage tank helps maintain a consistent water temperature and reduces energy waste.
The Role of Collectors in Solar Systems
A solar hot water system uses a solar collector to heat the water stored in a tank. The collector area determines how much sunlight can be absorbed for water heating. If your collector area is too small, the system may rely heavily on electric or gas boosting, increasing energy use.
Larger systems with more collectors and a bigger tank size can store enough hot water to meet daily demand, but the system must still match your household’s hot water consumption. Brisbane’s climate provides ideal conditions for solar water heaters to perform efficiently throughout the year.
When installed correctly, a solar system can supply up to 80 per cent of your household’s water heating needs.
Heat Pump Systems for Modern Homes
Heat pump water heaters are becoming popular across Australia for their energy-efficient performance. A heat pump uses ambient air to heat water instead of direct sunlight, making it a great option when a solar collector is impractical.
To size a heat pump water heater properly, you need to consider your household size and how much hot water your household uses daily. Heat pump systems work best when they match the hot water demand of your home.
A small family might need a 200 litre heat pump system, while a larger household could require a 300–400 litre unit. The system heats water gradually and stores it in a well-insulated tank, keeping energy use low while maintaining the desired hot water temperature.
Electric and Gas Water Heating Options
Electric hot water and gas hot water systems remain common in many Australian homes. Each type of water heater has its own sizing requirements.
Electric storage water heaters are ideal for smaller households or off-peak operation. Gas storage systems heat water faster and suit larger families. If you prefer instant heating, gas continuous flow systems can heat water on demand, supplying consistent hot water without needing a tank.
For system sizing, you’ll need to determine the flow rate in litres per minute and the temperature rise required to heat incoming cold water to your desired hot water temperature. A typical gas continuous flow unit delivers around 20 to 26 litres per minute, suitable for multiple hot water outlets.
When installing a new hot water system, consider your water appliances, number of hot water outlets, and the amount of hot water your household uses daily.
Matching System Size with Energy Efficiency
An oversized or undersized hot water unit affects energy efficiency. A system that is too small will run out of hot water, while a system that is too large wastes energy heating water you do not use.
The system you choose must match your daily hot water usage, incoming water temperature, and heating capacity. Modern water heating systems like solar, heat pump, and energy-efficient electric or gas units can significantly reduce your household’s energy use.
When investing in a system, it’s smart to plan for the future. A new water heater that fits your household’s growth ensures long-term savings and consistent hot water for years to come.
Getting Expert Help
If you are unsure about what water system you need or how to determine what size hot water system fits your home, a professional plumber can help. Experts consider your household size, water usage patterns, and type of water heater to recommend the right size.
Professional advice ensures the system heats water efficiently, provides enough hot water, and keeps energy costs manageable.
For trusted installation and honest guidance, All Kind Gas & Plumbing provides tailored hot water system selection and installation services across Brisbane. Our qualified team can help you choose the right system for your home and ensure reliable hot water every day.
Frequently Asked Questions
1. How do I determine the right hot water system size for my home?
It depends on household size, water usage, and heating preference. Larger families typically need bigger storage tanks or higher flow rate systems.
2. What happens if the system is too small?
A small system may run out of hot water during high-demand times, leaving insufficient supply for multiple hot water outlets.
3. Is a heat pump water heater energy-efficient?
Yes. Heat pump water systems use air to heat water, making them one of the most energy-efficient water heating options available.
4. Should I choose gas or electric water heating?
Gas systems heat water quickly, while electric systems are reliable and cost-effective when paired with solar PV or off-peak tariffs.
5. When should I replace my current hot water system?
Consider a new hot water system when your existing one no longer provides enough hot water or has frequent heating problems.
