June 5, 2025

What Size Hot Water System Do You Need? Guide for Perth Homeowners

Author:

Proud Plumbing

Choosing the correct hot water system capacity for your Perth home is essential for ensuring you have enough hot water without wasting energy on oversized units. Many homeowners struggle with this decision, unsure whether to select a 50L, 80L, 130L, 160L, or 250L hot water system for their household needs. The appropriate system size depends primarily on the number of people in your household and your typical usage patterns — generally, a family of 2–3 people requires a 130L system, while larger families of 4–5 people need a 160L or 250L system.

Perth’s unique water conditions also influence which hot water unit will perform best for your home. Certain systems may operate more efficiently year-round depending on factors like seasonal water temperatures and usage peaks. Understanding these considerations helps you make a cost-effective choice that delivers both comfort and energy efficiency.

Water usage habits vary significantly between households, even with the same number of occupants. If you often run multiple hot water appliances at once or prefer long showers, you may need to upsize from the general recommendation. On the other hand, homes with lower hot water demand may save money by opting for a smaller, more efficient unit.

Selecting a system with the right capacity balances your household’s daily consumption with available space, operating costs, and your home’s infrastructure.

Hot Water System Size Guide: Matching Capacity to Household Size

One of the most common questions Perth homeowners ask is: “What size hot water system do I need?” A correctly sized unit ensures you always have enough hot water without overspending on your energy bills to heat unused capacity.

The ideal system depends on three key factors:

Number of people in your home
Your daily hot water usage habits
System type — storage vs continuous flow

To help you decide, here’s a quick-reference table matching household size with recommended system capacities:

Household Size	Recommended Storage Tank Size	Recommended Continuous Flow Rate	Best For
1–2 people	90–130 litres	16–20 litres per minute	Small homes or units
3–4 people	160–250 litres	20–26 litres per minute	Medium-sized families
5+ people	270–400 litres	26L/min or dual systems	Large homes or high usage

It’s also helpful to understand typical hot water usage:

Shower: 10–15L per minute
Washing machine: 20–30L per cycle
Dishwasher: 15–20L per cycle
Bath: 80–150L per fill

importance of same day hot water system repairs

Estimating Your Household’s Hot Water Usage

Understanding your household’s daily hot water consumption is key to choosing the right system size. Below are some practical ways to estimate usage and plan accordingly:

Monitor Your Water Meter

Turn off all taps and water-using appliances, then take a reading of your water meter. Avoid using water for 1–2 hours and check again. If the reading has changed, it gives you an indication of background usage or possible leaks.

Measure Appliance Water Use

Check the user manuals or energy rating labels on your appliances. For example:

Dishwashers use approximately 15–20 litres per cycle
Washing machines use 50–100 litres per cycle, depending on load size and type
Multiply by how often you use them each week for a clearer picture.

Track Shower Flow Rates

Use a flow rate testing device or a basic bucket and timer method to determine how much hot water your shower uses per minute. Most standard showerheads use between 10–15 litres per minute. Multiply this by the number of showers taken daily to calculate usage.

Account for Seasonal Changes

Hot water use tends to increase in winter due to longer showers and colder water entering the system. When sizing a system, plan for your highest demand periods rather than just average usage.

Different Types of Systems

Storage tank systems heat and maintain a fixed volume of water. They come in electric, gas, solar, and heat pump variations, each with different recovery rates after water usage.

Continuous flow systems (instantaneous) heat water on demand. Rated by flow rate (litres per minute), they’re ideal for homes needing consistent hot water without the bulk of storage tanks.

Heat pump hot water systems are increasingly popular in Perth due to their energy efficiency. They extract heat from the air to warm water, using about one-third the electricity of traditional electric units.

Solar hot water systems take advantage of Perth’s abundant sunlight to reduce energy use. These typically include a backup element for cloudy days and are sized according to collector area and tank capacity.

Tank Considerations

Storage tank dimensions influence installation feasibility. A standard 135L tank is around 1.5m tall and 50cm wide, while a 270L system may exceed 1.8m in height.

Indoor tanks reduce heat loss but require ventilation (especially gas units), while outdoor tanks need weather protection and insulation. Water pressure also matters—elevated tanks offer gravity-fed pressure; ground tanks may need a pressure pump.

Recovery rate—how quickly the system reheats after use—is another factor. A gas hot water system typically recovers faster than an electric hot water system, which is important during high-demand periods.

hot water system outdoors against a wall

Key Factors Influencing System Size in Perth

Your ideal hot water system size in Perth depends on more than just household size. Climate, usage timing, and system technology also play a role.

Climate Considerations for Hot Water Systems in Perth

Perth’s climate plays a significant role in determining how hard your hot water system needs to work—particularly during colder months.

Average Incoming Water Temperatures

In summer, Perth’s incoming water temperature can reach up to 25°C, but in winter it drops to around 13–15°C. This means your system must work harder to reach your preferred water temperature, especially during June to August.

Winter Performance

While hot water demand may be lower in summer, it increases significantly in winter—not just due to cooler water, but also longer showers and more frequent use. It’s important to size your system based on winter demand to avoid shortfalls during peak usage periods.

Solar System Efficiency in Perth

Perth enjoys over 8 hours of sunlight a day on average, making it ideal for solar hot water systems. However, cloudy days in winter can reduce performance. Ensure your solar system includes a backup booster (electric or gas) to maintain consistent hot water availability throughout the year.

Temperature Rise and Why It Matters for Sizing

Hot water systems work by heating incoming cold water to your desired temperature. The difference between the starting water temperature and the target temperature is known as the temperature rise. The greater the temperature rise required, the more energy your system must use to deliver hot water at a consistent temperature.

Temperature Rise Formula: Desired Hot Water Temperature – Incoming Cold Water Temperature

For example, if your desired hot water temperature is 50°C and your incoming water is 15°C (a typical winter value in Perth), the system needs to provide a 35°C rise. Systems in colder regions or during winter months must be more powerful or have greater capacity to deliver adequate hot water quickly and efficiently.

Household Size and Hot Water Demand

Refer to the table above for typical sizing recommendations. Adjust these guidelines based on habits—teenagers, for example, tend to use more hot water than adults.

Planning for future changes is also wise. If you expect your household to grow, a slightly larger system may prevent future upgrades.

Peak Usage Patterns

The timing of hot water use influences system sizing. Morning and evening peaks are common in Perth households.

Determine whether your home needs:

A larger tank for simultaneous use
A continuous flow system for staggered use
A hybrid or dual system setup

If multiple showers, appliance cycles, and peak energy use occur at once, a higher-capacity system or faster-recovery unit may be necessary. Some Perth residents opt for gas or heat pump systems to reduce peak electricity costs.

Sizing Recommendations for Perth Homes

Small Households

Homes with 1–2 occupants typically require a 90L storage tank. These units suit apartments or smaller houses and offer energy-efficient performance. A continuous flow system delivering 16–26L/min is also effective for small households.

Depending on your routine (e.g. back-to-back showers or appliance overlap), you might benefit from going one size up for reliability.

Medium to Large Households

Households with 3–4 people typically need a 135–170L storage tank, while families of 5+ may require a 270–400L system.

A 26L/min gas continuous flow unit provides consistent supply for large households, especially during busy mornings. These systems are well-suited to Perth’s summer and winter usage fluctuations.

Improving Energy Efficiency Through Smart System Selection

Choosing an energy-efficient hot water system can lower your running costs and allow for a smaller unit without compromising on supply. Here are some key considerations:

Select systems with higher energy star ratings to reduce long-term energy use
Consider heat pump or solar systems, which are significantly more efficient than conventional electric units
Connect electric systems to off-peak tariffs to reduce electricity costs
Use water-saving fixtures to reduce demand and allow for smaller system sizing
Insulate your pipes and hot water tank to minimise heat loss

Comparing Hot Water System Types & Their Sizes

Understanding each system type helps match capacity to household demand while considering efficiency and cost.

Electric Hot Water Systems

1–2 people: 50L–130L
3–4 people: 125L–160L
5+ people: 250L–315L

Electric systems are easy to install and versatile but can be more costly to run unless connected to off-peak tariffs. Many now feature improved insulation and smart learning technology.

Gas Hot Water Systems

Gas storage units typically range from 135L–170L, while continuous flow systems are sized by litres per minute. Natural gas is cost-effective in Perth; LPG is an alternative if mains gas isn’t available.

Gas systems recover quickly and are energy efficient, but installation may require flueing or ventilation.

Solar and Heat Pump Water Heating Options

Solar: Typically 270L–340L tanks
Heat Pumps: Available in 170L, 250L, and 315L capacities

Solar systems use roof-mounted collectors and often include a booster. Heat pumps draw heat from the air and maintain efficiency even during cooler Perth winters.

Both options qualify for rebates and reduce long-term energy costs, making them excellent investments for most Perth households.

Budgeting and Planning for the Future

When selecting your hot water system, it’s important to think beyond your immediate needs. A system that suits your household now might fall short in the near future.

If you’re planning a family or expecting new residents, choose a slightly larger system to accommodate growth
Renovations, such as adding bathrooms or laundry areas, will increase your water usage
Investing in a system that can handle modest increases in demand helps you avoid early replacement costs
At the same time, avoid over-sizing, as this can lead to higher operating costs without added benefit
Always consider maintenance costs, some systems require more frequent maintenance than others

Need More Information? Contact Proud Plumbing and Gas Today

Our team at Proud Plumbing and Gas specialises in helping Perth homeowners select the right hot water system for their needs.

We offer free consultations to assess your household requirements and recommend the most suitable unit—whether storage, continuous flow, solar, or heat pump.

We service all Perth metro areas and can typically schedule appointments within 48 hours. Our friendly staff will ask about your current system, household size, and usage patterns to provide tailored advice.

Choosing the right size system improves both performance and efficiency—too small and you’ll run out of hot water; too large and you’ll waste energy.

If you’re ready to upgrade or need advice about what size hot water system to get, reach out to Proud Plumbing and Gas today.

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