Heat Pump Hot Water Sizing Calculator

What Size Heat Pump Hot Water System Do You Need?

Heat pump hot water systems work by extracting heat from ambient air rather than generating heat directly, making them 3–5 times more energy-efficient than conventional electric storage systems. Choosing the right tank size is the most important decision - too small and the system runs continuously in boost mode; too large and you're paying for capacity you don't use.

As a general guide, Australian households need approximately 50 litres of tank capacity per person for average usage. A family of four typically needs a 200–270 litre system, while a couple might be well-served by a 160–200 litre tank.

How Does Climate Zone Affect Heat Pump Performance?

Heat pumps extract heat from ambient air, so their efficiency (measured as Coefficient of Performance, or COP) varies with outdoor temperature. In hot climates like Queensland and the Northern Territory, a well-sized heat pump can achieve a COP of 4.5 or higher - meaning it delivers 4.5 kWh of heat for every 1 kWh of electricity consumed. In cool climates like Melbourne, Hobart, and the highlands, the effective COP in winter typically falls to 2.5–3.0.

Cooler climates also require larger tank sizes, because the system has less ambient heat to work with during winter and needs more stored capacity to meet demand without relying on the electric boost element.

How Much Do Heat Pump Hot Water Systems Cost?

Installed costs in Australia vary by brand, size, and location. As a guide:

• 160–200 litre systems: $2,500–$3,500 installed
• 200–270 litre systems: $3,000–$4,500 installed
• 300–315 litre systems: $3,500–$5,500 installed

These prices include supply and standard installation by a licensed plumber. Additional costs may apply for complex installations, new electrical circuits, or repositioning the unit.

Rebates and Incentives for Heat Pump Hot Water

Heat pump hot water systems are eligible for Small-scale Technology Certificates (STCs) under the federal government's renewable energy scheme, which reduces the upfront cost at the point of sale. The STC entitlement depends on the system's rated output and your location's solar zone.

State-based incentives also apply in Victoria (through the Victorian Energy Upgrades program), South Australia, and other states. Check the federal energy website and your state government's energy efficiency program for current rebates in your area.

Heat Pump vs Electric vs Gas: Which Has the Lowest Running Cost?

On current Australian electricity tariffs, a heat pump hot water system typically costs $150–$300 per year to run for an average household - compared to $600–$900 for a conventional electric storage system and $400–$700 for a gas storage system. If you have rooftop solar and can time the heat pump to run during solar generation hours, annual running costs can fall to $50–$150.

For more on home battery systems and maximising solar self-consumption, visit our home batteries hub.