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Hot-water planning

Hot-water systems: identify the options for a household

Start by identifying the existing water heater and fuel supply. A suitable replacement needs to meet household demand and fit the property as well as have an acceptable running cost. System labels alone cannot establish the best choice.

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Use the label and connections to identify the system

Record the manufacturer, model and tank information from an accessible label, without opening electrical or gas equipment. Check the bill or bottle invoice for fuel type. A tank can belong to several technologies, so its appearance alone is not enough. An installer can resolve an uncertain identification.

Electric storage
A resistance element heats stored water. Check whether its electricity is billed on a general or controlled-load tariff.
Heat pump
An electrically powered unit transfers heat from surrounding air to stored water. Check the model and installation requirements, including airflow and noise location.
Gas storage
A gas burner heats a tank. Confirm whether the supply is mains natural gas or bottled LPG.
Instantaneous gas
A gas unit heats water as it is drawn. Confirm fuel type and ask about the flow required when several outlets operate.
Gas-boosted solar hot water
Solar-thermal collectors supply heat and a gas booster supplies the balance. These collectors are different from rooftop panels that generate electricity.

YourHome’s system guide provides further background. HotWaterWise models the five categories above; it does not supply a product-by-product performance assessment.

Prepare a shortlist that an installer can assess

Bring the household’s demand estimate, existing system details, energy bill and photographs of the proposed location to the discussion. Ask about recovery after heavy use, suitable storage or flow, available space, noise, electrical capacity, gas connections, roof conditions where relevant and access for servicing.

Request an itemised installed quote. A product price can leave out removal, plumbing, wiring, controls or other site work. Compare warranties and servicing obligations alongside the quoted price. HotWaterWise does not inspect the property, size an installation or endorse a brand or installer.

Is gas cheaper than electricity?

There is no universal answer. Compare the energy input needed for the same hot-water demand, then apply the relevant unit price. Comparing cents per megajoule directly with cents per kilowatt-hour misses both the unit conversion and system efficiency.

The planning model uses efficiencies of 0.90 for electric storage, 0.55 for gas storage and 0.78 for instantaneous gas, with a heat-pump coefficient of performance (COP) of 3. Gas-boosted solar hot water uses a 0.70 solar-thermal fraction and 0.80 booster efficiency for the remaining heat. These assumptions enable a consistent comparison; they are not specifications for every appliance.

Fixed mains-gas supply charges are outside the numerical usage comparison. They may continue when another appliance still needs gas. For LPG, entered delivery and rental have separate rules explained in the 45 kg bottle guide. Household rooftop-PV self-consumption is excluded numerically, while the solar-thermal system is modelled separately.

Choose the next calculation for the decision

Rebates and certificates need a separate eligibility check. The complete assumptions and limitations are available in Methodology.

Sources and review

Official sources accessed and claims reviewed on 29 September 2026. Calculation examples use the HotWaterWise calculations and Methodology. Planning assumptions are not current retail offers. Recheck programme and tariff details before acting.