A standard electric resistance hot water system heats water the same way a kettle does: electricity passes through a resistive element, which converts that electrical energy into heat directly, at close to a one-to-one ratio. A heat pump hot water system works on an entirely different principle, and understanding that difference explains why heat pumps use meaningfully less electricity to heat the same volume of water.
Moving heat rather than generating it
A heat pump doesn't create heat from electricity directly, it uses electricity to run a compressor that extracts existing heat from the surrounding air and concentrates it, transferring that heat into the water in the storage tank. This is the same basic refrigeration cycle used in reverse-cycle air conditioners and refrigerators, just applied to heating water instead of cooling or heating air. Because the system is moving existing ambient heat rather than manufacturing it from scratch, it can deliver more heat energy into the water than the electrical energy it consumes to run the compressor, this is why heat pump systems are described as having a coefficient of performance (COP) typically well above 1, unlike a resistive element which cannot exceed a COP of 1.
Why this matters for household bills
Hot water is typically one of the larger single energy loads in an Australian household, particularly for households still using electric resistance or gas storage systems. Because a heat pump can deliver the same amount of hot water using meaningfully less electrical input than a resistive system, replacing an old resistive or gas system with a heat pump is one of the more commonly recommended electrification upgrades for households looking to reduce both running costs and gas dependency, alongside solar and battery investments.
Ambient temperature and performance
Because a heat pump extracts heat from the surrounding air, its efficiency is affected by ambient temperature, it generally performs best in mild-to-warm conditions, and its efficiency can reduce somewhat in cold climates or very cold overnight conditions, since there is less ambient heat available to extract. Most heat pump hot water units sold in Australia are designed with this in mind and remain effective across the climate range found in most of the country, but it's a reasonable question to raise with an installer if you're in a particularly cold climate zone, to confirm the specific unit's cold-weather performance rating.
Noise and placement considerations
Because a heat pump uses a compressor and fan (similar in principle to an air conditioner's outdoor unit), it produces some operating noise, generally modest but audible, particularly during the compressor's running cycle. Placement, away from bedroom windows or close neighbour boundaries, and in line with local council noise regulations, is worth discussing with your installer at the design stage, rather than after installation.
Sizing for household hot water demand
As with any hot water system, correct sizing matters, a unit too small for household demand can run out of hot water at peak times, while an oversized unit represents an unnecessary upfront cost. Sizing should be based on household size, typical usage patterns (for example, back-to-back showers in the morning), and the specific unit's recovery rate, and is best confirmed with an installer rather than estimated from generic household-size tables alone.
Incentives available for the switch
In several states, replacing an existing electric resistance or gas hot water system with a heat pump is a recognised activity under state energy efficiency certificate schemes, for example, under Victoria's VEU program, which can reduce the upfront cost of the switch. Eligibility and discount amounts depend on the specific equipment being replaced and current scheme settings, so it's worth confirming current eligibility with an accredited provider rather than assuming a specific discount applies.
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This article is general information, not financial or electrical advice. Program rules and eligibility change, confirm current settings with the relevant scheme or your Esena engineer before making decisions. Last reviewed: August 2026.