Hot Water Tariffs, Off-Peak, Timers & Solar
Hot Water Tariffs, Off-Peak, Timers & Solar
The cheapest time to heat water depends on your tariff, solar and when you actually need the hot water.
Heating overnight can make sense on a controlled-load tariff. Heating through the middle of the day can make more sense when you have rooftop solar. Heat pumps, electric storage and solar hot water can all benefit from good timing — but the right strategy is not the same for every home.
When Should Your Hot Water Heat?
Select your heater, solar setup, electricity arrangement and household demand. We will map the most useful heating strategy across a 24-hour day.
1 What type of hot water system do you have?
2 What solar setup do you have?
3 How is the electric hot water supply billed?
4 When is most hot water used?
5 What matters most?
The graph is a strategy guide rather than a retailer tariff schedule. Controlled-load switching is managed by the electricity network and exact availability can vary. Time-of-use periods and electricity prices vary by retailer and plan. Check your current bill before changing tariffs, timers, wiring or operating schedules.
When Is the Best Time to Heat Hot Water?
There is no single answer. A controlled-load electric tank may be designed around cheaper restricted supply. A solar household may benefit from heating during the day. A heat pump may work well with a daytime solar window. A household with two heavy demand periods may need more recovery flexibility than one overnight heating cycle provides.
No Solar
A controlled-load tariff can provide a lower electricity rate for suitable hot water systems in exchange for restricted supply availability.
Rooftop Solar
Daytime heating can increase the amount of your own solar generation used onsite instead of exporting it.
Heavy Demand
More heating availability can matter when the household uses a large amount of hot water both morning and evening.
Time of Use
Timing should consider the retailer's actual peak, shoulder and off-peak periods rather than assuming every plan uses the same hours.
Queensland Hot Water Tariff 31 vs Tariff 33
In South East Queensland, the names Tariff 31 and Tariff 33 are still commonly used for the two controlled-load arrangements, although electricity retailers may describe them as Controlled Load 1, Controlled Load 2, Super Economy, Economy or similar names.
| Feature | Tariff 31 / CL1 | Tariff 33 / CL2 |
|---|---|---|
| Supply style | More restricted controlled supply | Longer controlled-load availability |
| Energex description | Volume Controlled Night | Volume Controlled |
| Typical availability | 8+ hours, commonly around 10pm–7am | 16+ hours, generally outside 4pm–9pm |
| Hot-water behaviour | Often relies heavily on enough storage to carry the household through the day | Greater opportunity for recovery outside network peak periods |
| Useful when | The tank is appropriately sized and one main heating period can cover demand | The household benefits from greater heating availability or additional recovery |
| Exact electricity price | Depends on retailer and electricity plan | Depends on retailer and electricity plan |
How Hot Water Timing Fits Into a Typical Day
The value of a heating window depends on what kind of energy is available at that time and when the household needs the stored heat.
What Is a Controlled Load Hot Water Tariff?
A controlled load is a separately controlled electrical supply for suitable appliances such as electric hot water. In return for allowing the network to restrict when the circuit is energised, the appliance can generally receive a lower electricity rate than ordinary household usage.
Dedicated Circuit
The hot water system is normally wired through a dedicated controlled circuit associated with the meter.
Restricted Supply
The network decides when electricity is available within the controlled-load arrangement.
Separate Usage
Controlled-load energy normally appears separately from ordinary household electricity on the power bill.
Lower Rate
Controlled-load rates are generally priced below ordinary usage in exchange for allowing supply to be interrupted.
Storage Matters
The tank needs enough usable capacity to bridge periods when the controlled circuit is unavailable.
Retailer Still Matters
Your electricity retailer determines the actual retail tariff, rates, fees and plan conditions on the bill.
Is Tariff 31 Good for Hot Water?
Tariff 31 can work very well where the cylinder is large enough to store the household's required hot water between controlled heating periods.
Large Enough Storage Reserve
If the tank can heat during the available period and comfortably carry the household through the day, more limited supply may not be noticeable.
Heavy or Split Demand
A household that uses most of its storage in the morning and then needs another large amount in the evening may benefit from greater recovery availability.
Is Tariff 33 Better for Hot Water?
Tariff 33 generally provides a much broader controlled-load availability window than Tariff 31. That can improve recovery, but the retail rate may differ, so “more hours” does not automatically mean “cheaper overall.”
More Time to Recover
Longer availability can help replenish hot water between morning and evening use.
Not Permanent Power
The circuit remains under network control and can be interrupted during relevant network periods.
Compare Your Retailer
The actual value depends on your retailer's controlled-load rate and how much electricity the water heater consumes.
Should Hot Water Run During the Day With Solar Panels?
Often, yes — particularly when the alternative is exporting surplus rooftop solar and then buying electricity back later to heat the water.
Use Your Own Generation
A storage heater can absorb daytime solar generation and store the resulting heat for showers later in the day.
Target the Solar Window
Where the electrical arrangement allows it, a timer can concentrate heating into the stronger solar-production period.
Store Heat, Not Just Electricity
Heating the cylinder during the day effectively stores some of that solar energy as hot water for later use.
Electric Hot Water With Solar Panels
A conventional electric storage tank can be one of the simplest large household loads to shift into the middle of the day.
Solar Starts Producing
Rooftop PV generation rises after the morning period.
Heater Turns On
The element converts available electricity into stored heat.
Tank Reaches Temperature
The stored water becomes an energy reserve for later use.
Evening Showers Use Stored Heat
Hot water can be used after solar production has reduced or stopped.
Best Time to Run a Heat Pump Hot Water System With Solar
A daytime operating window can align a heat pump with rooftop solar generation while still leaving enough time to recover before the evening hot-water period.
Solar Is Building
Starting after the morning household peak can move heating into the stronger solar-production period.
Strong Solar Window
This period can provide a useful opportunity to consume generation onsite instead of exporting it.
Recovery Before Evening
Finishing the main heating cycle before heavy evening demand can leave the tank ready for showers and household use.
Should a Heat Pump Be on Tariff 31 or Tariff 33?
Do not assume a heat pump should automatically be wired the same way as the old electric storage cylinder it replaced.
Check the Heat Pump
The manufacturer, model controls, required operating availability and booster arrangement all matter when deciding how the system should be supplied.
Check the Recovery Window
A household may need enough available operating time for the heat pump to recover after heavy demand rather than relying on a short restricted period.
Should I Put a Timer on My Hot Water System?
A timer is useful when you control the circuit and there is a reason to concentrate heating into a particular part of the day.
Solar PV
A timer can move heating into the period when rooftop solar is usually producing strongly.
Time-of-Use Plan
Heating can be scheduled around the retailer's cheaper usage periods where the appliance and electrical arrangement allow it.
Avoid Peak Demand
Moving a large resistive load away from a demand-charge period can matter on some tariff structures.
Heat Pump Scheduling
Many heat pumps already provide internal scheduling, reducing the need for a separate external switching device.
Controlled Load
A timer cannot make a controlled circuit receive electricity while the network has switched that circuit off.
Reliability
A timer window that is too short can create a run-out problem if the tank does not have enough time to recover.
Does a Hot Water Timer Actually Save Money?
A timer does not magically make the same kilowatt-hour cheaper. It saves money when it changes where that energy comes from or what tariff applies when the heater uses it.
Solar Self-Consumption
A timer can substitute available solar generation for electricity that might otherwise have been purchased from the grid.
Time-of-Use Shifting
Moving heating from an expensive time period into a cheaper one can reduce the cost per kilowatt-hour.
Demand Management
On applicable demand plans, moving a large heating load away from the measured peak period may reduce the home's peak demand.
Flat Rate
If every grid kilowatt-hour costs the same and there is no solar or demand component, simply changing the clock time may make little difference to the usage rate.
When Should a Solar Hot Water Booster Run?
Solar thermal hot water is different from rooftop solar PV. The collectors are already heating the water directly, so the electric or gas booster is there to provide reliable temperature when solar contribution is insufficient.
Let Solar Contribute
Unnecessary electric boosting before a strong solar collection period can reduce how much useful solar heat the tank can accept.
Protect Reliability
The household still needs enough boosted hot water after poor weather or unusually heavy demand.
Follow System Controls
Booster operation should suit the particular solar system, thermostat and control arrangement rather than a generic timer copied from another installation.
Why Do I Run Out of Hot Water on Off-Peak?
Off-peak hot water works by heating a stored reserve during the available electricity window. If the household consumes that reserve before electricity becomes available again, the system can run cold even when nothing is broken.
Tank Heats
The controlled circuit becomes available and the heater restores the stored reserve.
Morning Use
Showers and other demand consume part of that reserve.
Limited Recovery
A more restricted controlled load may not immediately reheat everything that was used.
Evening Run-Out
A second demand period can exceed the remaining stored hot water.
Is Solar Hot Water Heating Better Than Controlled Load?
The comparison is not simply “free solar versus paid off-peak.” Surplus rooftop generation has an opportunity value because it may otherwise be exported, while moving the heater to another circuit can change the electricity rate and metering arrangement.
| Factor | Controlled Load | Daytime Solar Heating |
|---|---|---|
| Energy source | Grid electricity on a dedicated controlled-load tariff | Available rooftop PV first, with grid import if solar is insufficient |
| Timing | Determined partly by network availability | Can be targeted around household solar production where supply permits |
| Rate | Usually lower than ordinary usage, retailer dependent | Value depends on self-consumed solar, imports and forgone export credit |
| Recovery flexibility | Depends on controlled-load availability | Can be wider if connected to an appropriate permanent supply and controlled by timer or appliance |
| Best comparison | Compare the actual retailer rates, household demand, solar generation, export value and electrical configuration. | |
Should a Battery Run the Hot Water System?
A battery can run many household loads, but heating water directly from the battery is not automatically the most valuable use of stored electricity.
Use Solar First
Where practical, heating during active solar production can avoid charging the battery and then discharging it into the water heater later.
Preserve Battery Capacity
The household may value stored battery energy more for evening household loads after solar generation has stopped.
Household Strategy Matters
Battery size, solar generation, export rate, electricity plan and backup goals all affect the correct operating strategy.
Hot Water on a Time-of-Use Electricity Tariff
A time-of-use plan charges different electricity prices at different times. The important point is that the actual periods belong to your retailer plan — not to a universal Australian timetable.
Lower-Cost Window
A timer can move heating into the retailer's lower-cost period when the hot-water system and circuit allow it.
Avoid Expensive Periods
A large electric heating load can be deliberately kept away from a retailer's expensive peak period.
Grid Tariff May Not Be the Whole Story
With rooftop solar, daytime self-consumption can sometimes be more relevant than the grid price alone.
What About Demand Tariffs?
Demand tariffs can charge based partly on how much power the property draws during specified periods, not just the total kilowatt-hours consumed.
Electric Element Is a Large Load
A resistive water heater can materially add to household demand while its element is operating.
Timing Can Matter
Moving heating outside the plan's demand measurement period can alter the way the load contributes to the bill.
Controlled Load Can Be Separate
Economy-tariff equipment may be treated separately from the household's main demand tariff, depending on the retail arrangement.
Check the Retailer Plan
Demand charging structures vary, so the actual plan document matters more than a generic peak-time assumption.
How Do I Know What Hot Water Tariff I Am On?
Start with the electricity bill. Controlled-load electricity is usually listed separately from the main household usage.
Find Usage Charges
Look for the section showing the different electricity usage rates.
Look for Controlled Load
It may be described as Tariff 31, Tariff 33, CL1, CL2, Economy, Super Economy or another retailer name.
Compare kWh Usage
The separate controlled-load line shows how much electricity is being billed to that circuit.
Ask the Retailer
If the bill is unclear, the electricity retailer can confirm the tariff and applicable retail rates.
Smart Meters, Timers and Hot Water
A smart meter allows electricity usage to be recorded across different periods, but the meter itself does not automatically mean the water heater is being operated at the cheapest time.
Meter Records Usage
Interval data can show when household electricity is being consumed.
Tariff Sets the Price
Your retail electricity plan determines which rates apply to the recorded periods.
Heater Controls the Load
The circuit arrangement, controlled load, timer or internal appliance schedule determines when the water heater actually operates.
Hot Water Timing Strategy by System Type
| System | Main Timing Opportunity | Main Limitation |
|---|---|---|
| Electric storage | Controlled load, time-of-use shifting or daytime solar heating | Tank must have enough capacity and recovery for the chosen heating window |
| Heat pump | Daytime solar-aligned scheduling can be attractive where permitted by the model and circuit | Needs sufficient operating time to recover |
| Solar thermal | Allow solar contribution and use booster intelligently | Weather and solar contribution vary |
| Gas storage | Electricity tariff timing generally has little influence on primary water heating | Gas usage and burner recovery are more relevant |
| Instant gas | Heats on demand rather than storing a large heated reserve | Electricity timer strategy is not the main running-cost lever |
Hot Water Tariff, Off-Peak, Timer & Solar FAQs
What is Tariff 31 hot water?
Tariff 31 is a common Queensland name for the more restricted controlled-load electricity supply, also referred to by names such as Controlled Load 1 or Super Economy. Energex currently describes it as providing at least eight hours of supply, commonly around the overnight period, although actual switching can vary.
What is Tariff 33 hot water?
Tariff 33 is a Queensland controlled-load arrangement with broader availability than Tariff 31. Energex currently describes it as providing at least 16 hours of supply, generally outside the evening network peak period.
Is Tariff 31 cheaper than Tariff 33?
Retail prices depend on the electricity retailer and plan. Tariff 31 is more restricted, while Tariff 33 provides greater availability. Compare the actual rates on your electricity plan rather than assuming one will always produce the lowest annual bill.
What is Controlled Load 1?
Controlled Load 1 is a retailer term commonly associated in Queensland with the more restricted Tariff 31 style of controlled electricity supply.
What is Controlled Load 2?
Controlled Load 2 is commonly associated in Queensland with the broader Tariff 33 style of controlled supply, which provides more electricity availability for loads such as hot water.
What time does off-peak hot water turn on in Queensland?
There is not one guaranteed switching time. Energex currently describes the more restricted Tariff 31 arrangement as commonly providing supply around 10pm to 7am, while Tariff 33 has much broader availability. Exact controlled-load switching can change with network conditions.
Can Tariff 33 turn on during the day?
Yes. Energex describes Tariff 33 as having broad availability, generally outside the evening peak period, and network-controlled schedules can include daytime supply.
Why has my off-peak hot water started heating during the day?
Network operators can alter controlled-load switching patterns. Energex has specifically noted changes that make greater use of the middle of the day as rooftop solar generation increases across the network.
Should I heat hot water during the day if I have solar?
Daytime heating can increase solar self-consumption where your circuit and hot water system allow it. Whether it is cheaper than controlled load depends on your electricity rates, solar generation, export value and electrical arrangement.
What is the best time to run a heat pump with solar?
A daytime window covering the stronger solar-production period can work well for many households. The exact start and finish times should allow the particular heat pump enough time to recover before the household's main hot-water demand.
Should my heat pump run overnight or during the day?
It depends on the electricity tariff, rooftop solar, system controls and household demand. A home with spare daytime solar may favour daytime operation, while a property using a suitable controlled-load arrangement may have a different cost comparison.
Can I put a timer on electric hot water?
A timer can be useful where the electrical supply arrangement allows it, particularly for solar self-consumption or time-of-use pricing. The switching equipment and electrical work need to suit the heater circuit.
Does a hot water timer save electricity?
A timer mainly changes when the electricity is used. Savings usually come from using cheaper tariff periods, consuming rooftop solar or avoiding demand periods rather than the timer itself eliminating the energy needed to heat the water.
Can I use a timer on Tariff 31?
A timer cannot make electricity available while the network-controlled circuit is switched off. Any timer on a controlled-load circuit can only operate within periods when supply is actually available.
Why do I run out of hot water on Tariff 31?
The household may be using the stored reserve before the next substantial heating opportunity. Tank size, household demand and restricted recovery time all need to be considered.
Would Tariff 33 stop me running out of hot water?
The broader supply availability can improve recovery compared with a more restricted controlled load, but it will not fix an undersized tank or a faulty water heater. The actual electricity rate should also be compared.
Should I move my electric hot water off controlled load if I have solar?
Not automatically. Compare your controlled-load rate, normal electricity rate, rooftop solar generation, solar export value and any cost of changing the circuit or metering arrangement.
Is hot water a good way to use excess solar?
Storage hot water can be a useful flexible daytime load because electricity used while the heater runs can be stored as heat in the tank and used later.
Should a battery power my hot water system?
It depends on the household energy strategy. Where sufficient rooftop solar is available, running hot water directly during the solar-production period can avoid charging the battery and then discharging it into the heater later.
What is the best time to boost solar hot water?
Booster timing should suit the particular solar hot water system, household demand and expected solar contribution. The aim is to maintain reliable hot water without unnecessarily replacing useful solar heating with paid backup energy.
How do I know if my hot water is on off-peak?
Check the electricity bill for a separate controlled-load usage line. It may be labelled Tariff 31, Tariff 33, Controlled Load 1, Controlled Load 2, Economy, Super Economy or another retailer-specific description.
Is off-peak the same as controlled load?
The terms are often used interchangeably in everyday conversation, but controlled load specifically refers to a dedicated appliance supply that can be switched by the electricity network. Time-of-use off-peak pricing on the household supply is a different tariff arrangement.
Is a time-of-use tariff the same as Tariff 33?
No. A time-of-use plan changes the price of electricity on the household supply according to the time. Tariff 33 is a separate controlled-load supply arrangement for eligible appliances.
Does a smart meter automatically put hot water on off-peak?
No. A smart meter records interval usage, but the hot water tariff and circuit arrangement still depend on the electricity plan, metering configuration and how the appliance is connected.
Does instant gas need an off-peak tariff?
No. Instant gas heats water on demand using gas as its primary heating energy, so an electric controlled-load tariff is not the main running-cost consideration.
Heat the Water When the Energy Makes the Most Sense
The right setup can be overnight controlled load, broader Tariff 33 recovery, daytime solar heating, a heat-pump schedule or a combination of tariff and storage strategy. The important part is matching the heater, household demand and electricity plan rather than choosing a timer in isolation.