Hot water system timer: what it does and whether it is worth fitting
A timer on a hot water system cuts heating hours, not the heat you use. For many households the saving is smaller than the sales pitch suggests.
A hot water system timer switches the power to your tank off for part of the day. The tank still loses a little heat while it is off. And it still has to reheat what you use. The timer changes when the heating happens, not how much hot water you need.
That is why the benefit depends on your tariff and your habits. On a flat tariff, the sums are modest. If your retailer charges different rates at different hours, shifting the heating can matter more.
What does a hot water timer actually do?
It is a time switch on the supply to the tank. You set the hours the tank may heat. Outside them the element is off and the water slowly cools through the tank wall.
A well insulated tank loses heat slowly, so a few hours off costs little. A very old or poorly insulated tank loses more, and a timer on that tank mostly makes the water cooler by evening.
When is a timer worth it?
It is worth considering if your electricity plan charges different rates at different times of day and your tank is large enough to coast through the hours it is off. It is hardest to justify on a flat rate.
If you have an off peak supply, the timing is already controlled for you, so a second timer adds nothing. Our page on off peak hot water explains that arrangement. We print no tariffs or savings figures, because they vary by state and plan.
Which systems can take a timer?
| System | Does a timer make sense? |
|---|---|
| Electric storage | Yes, if your tariff varies by time and the tank is large enough. |
| Heat pump | Many have built-in scheduling. Check the manual before adding anything. |
| Solar with electric boost | Sometimes. Boost timing can matter, but the sun does most of the work. |
| Gas continuous flow | No. There is no tank to keep hot. |
Will a timer make you run out of hot water?
It can. If the heating hours are too short for the size of the tank, the water is warm at breakfast and cold by dinner. That is the price of squeezing the schedule too hard.
If the water is already warm rather than hot, a timer is not the answer. See lukewarm hot water first. A worn element or a failed thermostat will not be fixed by a switch.
Our view: fit one only if the numbers are clear
Do not buy a timer on the strength of a general promise to save. Look at your plan, find out whether rates really differ by hour, and ask your retailer. If they do not, leave the system alone.
What can you do yourself, and where does it stop?
Checking your tariff, noting how long the water lasts and asking your retailer or installer whether your model has built-in scheduling are all yours. None needs a licence.
This far, and no further. Fitting a time switch means working on the switchboard or the tank's supply, which is licensed electrical work. Do not open the switchboard or the electrical enclosure of the tank.
Licensing and compliance are set by each state and territory. Check with the regulator where you live, and ask for the licence number before any work starts.
How to check whether a timer would help you
You can find out without spending anything. Follow these steps.
- Read your electricity plan. Find out whether rates really differ by hour.
- Ask your retailer for current figures. They change by state and plan.
- Check whether you have off peak. If so, the timing is already controlled.
- Look at your tank. A large, well insulated tank coasts through hours when the element is off.
- Note how long the water lasts. If it runs out already, a timer will make that worse.
- Ask whether your model has built-in scheduling. Many heat pumps do.
If the rates do not differ by hour, leave the system alone.
Timer problems and what to try first
| Problem | Likely cause | Try |
|---|---|---|
| Water cold by evening | Heating hours too short for the tank | Lengthen the heating window |
| Water only warm all day | Worn element or failed thermostat | See lukewarm hot water; a switch will not fix it |
| No effect on the bill | Flat tariff, or off peak already controls timing | Check your plan with your retailer |
| Timer on a gas continuous flow unit | No tank to keep hot | Do not fit one |
| Opening the switchboard to fit one | Licensed electrical work | Hire a licensed electrician; ask for the licence number |
Frequently asked questions
Does a hot water system timer save money?
It depends on your tariff. If your plan charges different rates at different hours, shifting the heating can help. On a flat rate the saving is usually small. Ask your retailer for current figures, because we print none.
Can I put a timer on any hot water system?
Electric storage tanks are the usual fit. Many heat pumps have scheduling built in. Gas continuous flow systems have no tank to keep hot, so a timer does nothing there.
Will a timer make me run out of hot water?
It can, if the heating hours are too short for the tank size. The water is warm in the morning and cold by evening. Make the hours fit your use, not the other way round.
Can I fit a hot water timer myself?
No. It involves the switchboard or the tank's electrical supply, which is licensed electrical work in every state and territory. You can check your tariff and ask whether your model has built-in scheduling.
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)