Off peak hot water: how it works and whether it suits your house
Off peak hot water only works if your tank holds enough to last the day. Here is how the arrangement works, what it needs, and when to question it.
Off peak hot water means your electric storage tank is heated only during set overnight hours, on a separate and cheaper electricity supply. The tank does its heating while demand on the grid is low, then holds the heat until you need it.
The catch is simple. A tank that heats only at night must store the whole day's hot water in one go. If it is too small, you run out in the evening and nothing you do at the tap fixes that.
How does an off peak hot water system work?
The tank's heating element is wired to its own circuit, which the electricity distributor switches on and off. Heating is allowed only in a fixed window, usually overnight. Outside that window the element is simply cut off.
Which hours, and what the supply is called, differs between distributors and between states. Your electricity bill or your retailer will name the arrangement that applies to your address. Do not assume the neighbouring state works the same way.
| Question | What to find out |
|---|---|
| Is your tank on a separate supply? | Look for a separate line on your bill for a controlled or off peak supply. |
| When can it heat? | Ask your retailer or distributor for the heating hours that apply to you. |
| Is it big enough? | The tank must cover a full day of use from a single overnight heat. |
| Is the arrangement still offered? | Availability for new connections changes. Ask before you plan around it. |
Why does off peak hot water need a bigger tank?
Because the element gets one window a day. A tank that heats on demand can top itself up at any hour. An off peak tank cannot, so the volume is your whole day's supply.
A household that fits a normal tank to an off peak circuit tends to find the hot water is fine in the morning and gone by evening. Our guide to choosing the right size of hot water system covers how to think about it. When in doubt, size up.
Can you run out of hot water on off peak?
Yes, and it is the commonest complaint. Heavy use in one morning, visitors, or a cold snap can empty the tank before the next heating window opens. There is no boost between the hours.
If it keeps happening, the cause is usually volume rather than a fault. Check that before you pay for a repair. If the water is warm rather than gone, see our page on lukewarm hot water.
Is off peak hot water worth keeping?
Often yes, but not always. It suits a household with steady use and a properly sized tank. It suits a household with a small tank and uneven demand much less.
If you are replacing the system, do not just copy what was there. A heat pump or solar system changes the sums, and our comparison of the four system types is the place to start. We print no tariffs or running costs, because they vary by state and change every year. Get current figures from your retailer.
What can you do yourself, and where does it stop?
Reading your bill, finding the controlled supply line, noting how long the water lasts and asking your retailer about heating hours are all yours. None needs a licence.
This far, and no further. The switchboard, the controlled circuit and the connection to the tank are licensed electrical work. Replacing or altering the tank is licensed plumbing work. Do not open the electrical enclosure of the tank or the switchboard, and do not try to change which supply the tank is on.
Licensing and compliance are set by each state and territory. Check with the plumbing and electrical regulators where you live, and ask for the licence number before any work starts.
Frequently asked questions
What is off peak hot water?
It is an electric storage tank heated only during set overnight hours on a separate, cheaper supply. The tank stores the heat and you draw on it through the day. The hours depend on your distributor.
Why do I run out of hot water on off peak?
The element only gets one heating window a day, so the tank must hold your whole day's supply. Heavy use in one morning, visitors or cold weather can empty it before the next window. Volume is usually the cause, not a fault.
Is off peak hot water worth it?
It can be, for steady use and a tank sized for a full day. It suits a small tank with uneven demand much less. Ask your retailer for current tariffs, because we print no figures.
Can I change my hot water system to off peak myself?
No. The controlled circuit, the switchboard and the tank connection are licensed electrical work, and altering the tank is licensed plumbing work. You can read your bill and ask your retailer which supply you are on.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Australian Government, energy.gov.au. Hot water systems — types, installation and energy performance
- Australian Building Codes Board. National Construction Code — Volume Three (Plumbing Code of Australia)