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Selecting the right hot water system size is one of the most important decisions when upgrading or replacing your home's hot water supply.
A system that's incorrectly sized may leave your household without enough hot water during peak periods. The ideal hot water system size depends on your household size, water usage habits, number of bathrooms, and the type of system you choose.
How do I Know What Size Hot Water System I Need?
When determining the right hot water system size, consider the following factors:
Household Size
The number of people living in your home is the best starting point. Larger households typically require greater hot water capacity, particularly during morning and evening peak periods. If you regularly host guests or have family staying over, it's worth factoring in additional demand.
Number of Bathrooms and Hot Water Outlets
Homes with multiple bathrooms often require larger systems because several showers, taps or appliances may be used simultaneously. A single-bathroom home can often operate efficiently with a smaller system.
Hot Water Usage Habits
Hot water demand can vary significantly between households. Longer showers, multiple daily showers, frequent laundry loads and dishwasher use will all increase consumption.
Storage, Heat Pump or Continuous Flow?
Different technologies are sized in different ways:
Storage hot water systems store heated water in a tank.
Heat pump hot water systems use energy-efficient technology to heat and store water.
Continuous flow gas hot water systems heat water only when required, delivering hot water on demand without storing it.
Storage and Heat Pump Hot Water System Sizing
Storage and heat pump systems are generally selected based on tank capacity and household demand.
Model | Capacity | Suitable For | Bathrooms | Bedrooms |
GR Series | 180L to 300L | 3 to 6 people | Up to 2 | 3 to 4 |
AR Series | 300L & 340L | 6 to 7 people | Up to 3 | 4 to 5 |
Enviroflo S (5kW) | 250L & 315L | 5 to 6 people | 2 to 3 | 4 to 5 |
Enviroflo S (7kW) | 250L to 400L | 5 to 8 people | 2 to 3.5 | 4 to 5 |
These recommendations provide a useful guide, but actual requirements can vary depending on household behaviour and peak usage periods.
Continuous Flow Gas Hot Water System Sizing
Unlike storage systems, Rinnai Infinity continuous flow systems heat water as it passes through the unit. This means you don't have a limited tank capacity and won't run out of stored hot water.
Continuous flow sizing is based primarily on the number of showers and hot water outlets that may operate at the same time.
Model | Warm Climate | Cool Climate |
Infinity B12/16 | 1 shower | 1 shower |
Infinity B20 | 1 to 2 showers | 1 shower |
Infinity B26/28i | 1 to 3 showers | 1 to 2.5 showers |
Infinity 32 | 2 to 4 showers | 2 to 3 showers |
Climate is an important consideration because colder incoming water temperatures require greater heating capacity.
Common Hot Water System Sizing Questions
What Size Hot Water System for a Family of Four?
For a typical family of four, a storage or heat pump system in the 250L to 315L range is often suitable. For continuous flow systems, the right model depends on how many showers and appliances are likely to run simultaneously.
Is Continuous Flow Better for Large Families?
Continuous flow systems can be an excellent option for larger households because they provide hot water on demand. However, the system must still be correctly sized to support the number of simultaneous outlets being used.
Find the Right Hot Water System
While household size and bathroom count are helpful indicators, the best hot water system size depends on your unique usage patterns.