Hot Water Running Cost Calculator Australia

AUSTRALIA · HOT WATER CALCULATOR

Estimate hot water running costs in Australia from litres, temperature rise, system type and your own electricity or gas tariff — or calculate cost from a known annual energy-use figure.

HomeBillLab calculator

Estimate hot water running cost

Estimate the energy needed to heat a daily volume of water, or use a known annual electricity or gas energy figure. Enter your own tariff rather than a national-average rate.

Use your own tariff and product information. The water-use method is an engineering estimate of energy used to heat the water. Storage losses, pipe losses, booster use, climate and control settings can make real system energy use higher or lower.
L/day
°C
°C
c/kWh
days
Estimated annual running cost—Water-heating estimate only; see the notes below for system losses and other factors.
Thermal energy to water—
Input energy per active day—
Per active day—
Per week—
Monthly average—
Why is the water-use result only an estimate?

The formula calculates the heat added to the water, then converts that into purchased electricity or gas using the system performance figure. Real storage systems can also use energy through tank and pipe heat loss, reheating, boost elements, control settings and other operating conditions.

What should I use for a heat pump?

Use a model-specific COP or performance figure if you have one. A higher COP means less purchased electricity for the same amount of heat delivered to the water. If you have a tested or predicted annual energy-use figure, the Known energy use method may be more representative.

What should I use for gas efficiency?

Enter the efficiency as a decimal, such as 0.80 for 80%, using product or technical information where available. The calculator does not assume one universal gas-water-heater efficiency.

Privacy: calculations run in your browser. The numbers you enter are not submitted to HomeBillLab.

How the hot water running cost calculator works

Heating water requires energy to raise its temperature. The calculator first estimates the thermal energy delivered to the water from the litres used and the temperature rise. It then converts that heat requirement into purchased electricity or gas using the system information you enter.

Water-heating energy
Litres × 4.186 kJ/kg·°C × temperature rise ÷ 3,600 = thermal kWh delivered to the water.

For direct electric resistance heating, the tool compares that thermal requirement with your electricity tariff. For a heat pump, it divides the required heat by the COP you enter. For gas, it converts the heat requirement to megajoules and divides by the efficiency you enter before applying the gas usage rate.

Choose the method that matches the information you have

Water use method

Useful for scenario testing when you know or want to estimate daily hot-water litres, incoming water temperature and target hot-water temperature. It is a water-heating estimate rather than a full laboratory prediction of a specific storage system.

Known energy use method

Use this when a product registration, technical document, energy study or your own measurement gives an annual electricity figure in kWh or gas figure in MJ. It applies your tariff directly to that annual energy figure.

Hot water systems in Australia are not all labelled the same way

Unlike many household appliances, Australian water heaters are generally not required to display the familiar government Energy Rating Label. Electric storage, gas storage and gas instantaneous water heaters are subject to minimum energy performance requirements, while product information and registration data can still help compare systems. Heat-pump labelling requirements are also under regulatory development.

What can change real hot water running costs?

How much hot water you use

More litres and a larger temperature rise require more heat. Household size, shower length, flow rate, laundry and kitchen use can materially change demand.

Storage and distribution losses

Storage tanks keep water hot between uses, so tank, pipe and reheating losses can add energy beyond the heat delivered in the water itself.

System technology

Heat pumps transfer heat using electricity and can use substantially less electricity than conventional resistance water heating. Gas, solar and boosted systems have different operating characteristics.

Your tariff and operating time

Electric storage systems may use controlled-load or off-peak tariffs where available. Time-of-use prices and solar PV can also change the cost of when electricity is used.

Related Australian energy guides

Use these guides to check assumptions, follow worked examples and compare common household scenarios.

Browse all Hot Water guides

Official Australian references

Reviewed: 21 August 2026.

Hot water running cost calculator FAQs

Does the calculator include the daily electricity supply charge?

No. The supply charge is a property-level fixed charge and is not caused by the hot water system alone. Use the Electricity Bill Calculator when you want to estimate a whole household electricity bill including the daily supply charge.

Can I use this for a heat pump hot water system?

Yes. Select Heat pump and enter a model-specific COP or performance figure. If you have annual tested or predicted energy use, the Known energy use method can be more representative because it can incorporate more of the system behaviour.

Can I use an off-peak or controlled-load electricity rate?

Yes. If your hot water system is actually billed on a separate controlled-load or off-peak usage rate, enter that applicable c/kWh rate. Do not use a cheaper rate unless it genuinely applies to the system.

Why might my real cost be different?

Real energy use can vary with storage losses, climate, inlet-water temperature, thermostat settings, hot-water demand, pipe losses, heat-pump performance, solar contribution, boost operation and tariff structure.