Hot water is the quiet giant of Australian electricity bills. In a home with an electric storage system it is commonly the single biggest appliance, often a quarter or more of total usage, and unlike heating or cooling it works year round. Yet because the tank sits outside doing its job silently, almost nobody manages it. This guide covers how the systems differ, what they do to a bill, and the checks that make sure yours heats at the cheapest possible time.
First, know what you have
- Electric storage: a tank with a resistive element, heated in blocks and kept hot. The classic Australian setup, and the hungriest per litre of hot water.
- Heat pump: a tank heated by a compressor that pulls warmth from the air, typically using around a third or less of the electricity of a resistive tank for the same hot water. Dearer to buy, cheap to run, and government incentives frequently apply; check the official pages listed in our concessions guide alongside your State's energy programs.
- Continuous (instant) electric: heats water on demand, no tank. Small units suit low use; whole-house electric continuous systems draw hard while running.
- Solar hot water: panels or evacuated tubes with an electric booster; the booster is the part that shows up on your bill.
- Gas: off the electricity bill entirely, so out of scope here, though many gas households still weigh a future switch to a heat pump.
The bill often tells you which category you are in: a second usage line at a cheaper rate means your tank is on a separately metered circuit.
The tariff question: when does your tank heat?
For storage systems, the running cost has two ingredients: how much energy the tank uses, and what each kWh costs when it heats. The second is where most of the free money sits.
- On a controlled load, the network heats your tank in off-peak windows at a cheaper rate. This is the classic setup and still a good one; our controlled load guide explains the naming across States and how to spot it on your bill.
- On a general circuit with a time-of-use plan, a timer that heats the tank overnight or in cheap midday windows does the same job by scheduling; see our time-of-use guide.
- With solar on the roof, a timer or diverter that heats the tank in the middle of the day turns exported cents into avoided dollars, the same self-consumption logic as our solar guide.
- The failure mode is a tank heating at random on a full-price anytime rate. If your electric tank is on neither a controlled load nor any schedule, that is the first thing to fix, by asking your retailer and electrician what your meter supports.
Reading the signs on your bill
Your controlled load line is a free diagnostic: it tells you exactly what the tank consumed. Watch for a creeping controlled load line (a failing element, a stuck valve or a slow leak makes a tank work harder; our high bill checklist covers the pattern), and for a household mismatch (a big tank serving one or two people keeps more water hot than anyone uses; temperature and timer settings, or a smaller system at replacement time, claw that back). If you cannot see a controlled load line but you are sure you have an electric tank, it is heating at general rates, which is worth a phone call. The formula-first approach in our appliance running costs guide lets you put numbers on any of these.
When you compare plans, do not forget the tank
Because hot water is such a big usage slice, plans live and die on their controlled load rate for tank-owning households, and some plans do not publish one at all. Our free calculator takes your general usage and controlled load usage separately and prices every plan on both, tagging any plan where a missing controlled load rate forces the general rate. Pick your State and, in Queensland, New South Wales, Victoria, South Australia, Tasmania and the ACT, import real plans for your postcode from government data.
The tank cannot advocate for itself. Once a year, look at its line on the bill, confirm it heats in the cheap windows, and make sure the plan prices it properly. Fifteen minutes, and the quiet giant goes back to being quietly cheap.