A Simple Guide to Input, Output, Charging and Off-Peak Electricity
Storage heaters can be extremely effective when they are understood and controlled properly.
However, they work very differently from ordinary electric radiators.
A normal electric heater uses electricity at roughly the same time that it produces heat. A traditional storage heater does something different.
It uses electricity during a charging period to heat heavy thermal-storage material inside the heater. The stored heat is then released gradually into the room.
In simple terms:
Charge the heater → store the heat → release the heat when you need it.
With older storage heaters, particularly traditional models such as older Dimplex heaters, two controls are especially important:
Input determines how much heat you put into the heater.
Output determines how quickly you let that stored heat out.
Understanding that distinction is the key to using traditional storage heaters properly.
How Does a Storage Heater Work?
Inside a traditional storage heater are heavy heat-retaining blocks, often referred to as storage bricks.
During the designated charging period, electrical heating elements heat these blocks.
The heater then stores much of that thermal energy and gradually releases it into the room.
Therefore, unlike a conventional electric radiator, the heater does not necessarily need to be drawing electricity while it is keeping the room warm.
It may be releasing heat that was stored several hours earlier.
This is why storage heaters have traditionally been paired with off-peak electricity tariffs.
Why Charge Storage Heaters Overnight?
Traditional storage heating was designed to take advantage of electricity that was cheaper during certain off-peak hours.
Economy 7 is probably the best-known example.
Instead of using large amounts of electricity during the more expensive daytime period, the heater charges during the cheaper period and stores that energy for later.
Therefore, the basic idea is:
Cheaper electricity overnight → heat stored in the heater → heat released during the following day.
However, the exact off-peak hours depend on your meter, tariff, supplier and location.
So, don’t assume that every Economy 7 household receives cheap electricity at exactly the same times.
The Two Controls on Older Storage Heaters
Traditional storage heaters commonly have two controls.
They may be labelled:
- Input and Output
- Charge and Output
- Input and Room Temperature
- Or something similar
The exact wording varies.
However, on traditional manually controlled heaters, the principle is generally straightforward.
Input = How Much Heat Goes In
The Input control determines how much energy the heater stores during its charging period.
A higher input setting allows the heater to store more heat.
A lower input setting stores less.
Therefore, think of Input as deciding:
How much heat will I need for the next day?
If tomorrow will be very cold, you may need more stored heat.
If the weather is mild, you may need less.
Output = How Quickly Heat Comes Out
The Output control has a different purpose.
It affects how quickly the stored heat is released into the room.
Therefore, think of Output as deciding:
How quickly do I want to use the heat I have already stored?
This distinction is crucial.
Turning the Output up does not put more heat into the heater.
It simply allows the stored heat to escape more quickly.
Once that stored heat has been used, it is gone until the heater charges again.
Think of the Heater Like a Tank
A simple analogy makes traditional storage heaters much easier to understand.
Imagine that the heater is a tank.
Input fills the tank.
Output controls how quickly you empty it.
If you don’t put enough into the tank, you will run out.
However, even if you fill the tank completely, opening the outlet too far can empty it too quickly.
A storage heater behaves in much the same way.
You need enough heat stored to meet your needs, but you also need to release that heat at a sensible rate.
Why Does My Storage Heater Go Cold by Evening?
This is one of the most common problems with older storage heaters.
Suppose the heater charges overnight and is hot in the morning.
You then turn the Output control high.
The heater releases its stored heat quickly.
Your room may become very warm during the morning and afternoon.
However, by early evening, much of the stored heat may have been released.
The heater then feels cold.
This does not necessarily mean that the heater is faulty.
You may simply have used the stored heat too quickly.
Remember:
If all the stored heat comes out before the next charging period, the storage heater will go cold.
Turning the Output higher at that point cannot create more stored heat.
You have to wait for the next charging period unless the heater has a separate direct-acting boost or supplementary heater.
Why Is My Storage Heater Not Warm Enough?
The opposite can also happen.
If the heater does not store enough heat overnight, there may not be enough available for the following day.
For an older manually controlled heater, the Input setting may simply be too low for the weather conditions.
For example, a setting that works perfectly in October may not provide enough heat during a cold January day.
Therefore, traditional storage heaters often require some anticipation.
You are effectively deciding today how much heat you are likely to need tomorrow.
Input and the Weather
With older manually controlled storage heaters, the Input setting may need to change as the weather changes.
For example:
Mild weather
Lower input may be sufficient.
Cool weather
A moderate input may be appropriate.
Very cold weather
More stored heat may be required.
However, there is no universal number that works for every property.
A well-insulated flat may require much less heat than a draughty house.
Likewise, a large room may need more heat than a small bedroom.
Therefore, adjust gradually and learn how your particular property behaves.
Don’t Use Output to Compensate for Low Input
This is an easy mistake to make.
Suppose the room feels cold.
You turn the Output control higher.
The room becomes warmer.
It therefore seems as though the problem has been solved.
However, you are releasing the existing stored heat more quickly.
If the heater did not store enough energy in the first place, turning Output higher may simply mean that you run out of heat sooner.
The better question is:
Do I need more heat stored, or do I need the existing heat released faster?
Those are two different problems.
How to Use Output Through the Day
With a traditional manually controlled storage heater, it can make sense to keep the Output relatively restrained when you do not need much heat.
For example, if everyone is out during the day, releasing large amounts of stored heat into an empty room may waste the heat you wanted for the evening.
Instead, you may want to conserve more of the stored heat for later.
Then, when the room is occupied, you can increase the Output if required.
However, even with the Output low, an older storage heater will still release some heat naturally through its casing.
It cannot store the energy perfectly.
Why Does Heat Come Out Even With Output Turned Down?
Traditional storage heaters cannot hold all their heat indefinitely.
The storage blocks are extremely hot after charging.
Although the heater is insulated, some heat naturally escapes through the casing.
Therefore, even with the Output control set low, the room may still become warm.
The Output control mainly affects the additional controlled release of heat.
It does not turn the storage heater into a perfectly sealed container.
This is one reason older storage heaters can sometimes make rooms warmer than wanted earlier in the day.
Why Are Older Storage Heaters Sometimes Difficult to Use?
Traditional storage heaters require you to predict your future heating needs.
For example, imagine tonight is relatively mild.
You set the Input low.
However, the temperature drops unexpectedly tomorrow.
You may then discover that you did not store enough heat overnight.
The opposite can happen too.
You expect a cold day and set the Input high.
The following day turns out to be mild.
You now have a large amount of stored heat that the heater will gradually release whether you need all of it or not.
That is one of the main limitations of traditional manual storage heating.
What Happens During the Charging Period?
During the off-peak charging period, electricity is supplied to the heating elements inside the storage heater.
The elements heat the internal storage material.
As the blocks become hotter, more thermal energy is stored.
Once the charging period finishes, the electrical supply to the storage elements may stop.
However, the heater remains hot because the energy is now stored inside it.
The heater can then continue warming the room for many hours without the storage elements actively drawing electricity.
How Do I Know When My Storage Heater Is Charging?
This is not always obvious.
Depending on the installation, the heater may receive electricity automatically during the off-peak period.
You might notice:
- The heater becoming warmer overnight
- Electricity consumption increasing during the charging period
- Your smart meter or app showing higher overnight use
- A dedicated off-peak circuit becoming active
However, the controls and wiring vary between properties.
Therefore, if you are unsure when your storage heaters charge, check:
- Your electricity tariff
- Your meter arrangement
- Your heating controls
- The heater instructions
This information is particularly important before changing electricity supplier or tariff.
Storage Heaters and Economy 7
Economy 7 normally provides a cheaper electricity rate for approximately seven hours during the night or another defined off-peak period.
Traditional storage heaters can use this cheaper electricity to charge.
However, Economy 7 usually also has a different rate outside those hours.
Therefore, whether Economy 7 is good value depends on your overall electricity consumption, not simply whether you own storage heaters.
If a large proportion of your electricity use can take place during the cheaper period, the tariff may be advantageous.
However, if most of your electricity is consumed during the more expensive period, the calculation may be different.
Always compare the actual rates and your usage pattern.
Economy 10 and Other Arrangements
Some electrically heated homes have other tariff and meter arrangements.
For example, some have historically used tariffs offering additional cheaper periods during the day.
There are also legacy metering arrangements that can be more complicated than standard Economy 7.
Therefore, never assume that every storage-heated property works in exactly the same way.
Before changing tariff, find out:
What meter do I have?
When is my cheap-rate electricity available?
Which circuits receive that electricity?
How are my storage heaters controlled?
That can prevent unpleasant surprises later.
Be Careful When Changing Tariff
This deserves particular attention.
In some properties, traditional storage heaters are connected to dedicated circuits controlled by the electricity meter or associated switching equipment.
Therefore, changing meter or tariff arrangements without understanding the heating setup can affect how the heaters charge.
A tariff that looks cheaper on paper may not necessarily suit the way your heating system operates.
Before changing an unusual or legacy electricity tariff, understand exactly how your storage heating and hot water are supplied.
This is especially important if you also have an immersion-heated hot-water cylinder.
Storage Heaters and Hot Water
Many homes with traditional storage heating also use electricity to heat their domestic hot water.
A common arrangement is:
Storage heaters → space heating
Immersion heater → hot water
Both may take advantage of off-peak electricity.
For example, the storage heaters and lower immersion element may charge or heat during the cheaper overnight period.
A separate boost immersion may then provide additional hot water during the day if required.
Therefore, your heating, hot water, meter and electricity tariff may all be connected as one overall system.
Learn more about immersion heaters →
What Is a Boost Heater?
Some storage heaters include a separate direct-acting heating element.
This is often referred to as a boost, convector or supplementary heater.
Unlike the storage section, this element produces heat directly when you switch it on.
Therefore:
Storage heating → uses previously stored heat
Direct boost → uses electricity while producing additional heat
This distinction matters because the boost may use electricity at the rate applying at that moment.
If you use it during an expensive daytime period, it may cost considerably more than heat stored using cheaper off-peak electricity.
Does Boost Use Cheap Electricity?
Not necessarily.
This is one of the most important things to understand.
The storage element may be wired to charge only during designated off-peak hours.
However, a direct boost or convector function may be connected to the normal electricity supply so that it can operate whenever you need it.
Therefore, pressing Boost at 6pm may mean using electricity at the 6pm tariff rate, not the overnight storage-heating rate.
The exact arrangement varies, so check your heater, wiring and tariff.
Don’t assume that everything inside a storage heater automatically runs on cheap-rate electricity.
Older Dimplex Storage Heaters
Many UK homes still contain older Dimplex storage heaters with manual Input and Output controls.
Although individual models differ, understanding those two controls makes them much easier to manage.
Remember:
Input
Determines how much electrical energy is allowed into the storage section during the charging period and, therefore, how much heat is stored.
Output
Controls how readily the stored heat is released.
Therefore:
Too little Input → not enough heat stored
Too much Input → more heat stored than you may need
Output too high → stored heat released too quickly
Output lower → more heat retained for later, within the limits of the heater’s insulation
This is the fundamental operating principle of many traditional storage heaters.
A Practical Example
Imagine a storage heater charges overnight.
You wake at 7am and the heater is fully charged.
You want the living room warm at 7pm.
If you leave the Output high throughout the morning and afternoon, the heater may release much of its stored heat before you need it most.
By 7pm, it may be relatively cool.
Instead, keeping the Output lower earlier in the day can help retain more heat for later.
Then, when you are using the room, you can increase the Output as required.
However, if there was not enough Input overnight, there may still be insufficient heat available.
Therefore, you need to manage both sides of the equation.
What If the Heater Is Still Hot at Bedtime?
This can be a useful clue.
If a traditional storage heater remains very hot late at night just before the next charging period, you may have stored more heat than you actually needed.
In suitable circumstances, you might try reducing the Input slightly.
Then monitor comfort the following day.
The aim is not necessarily to have the heater completely cold every evening.
Instead, you are trying to find a setting that provides enough heat for the household without repeatedly storing far more than you use.
What If It Is Cold Too Early?
If the heater consistently becomes cold several hours before the next charge, ask two questions:
Was enough heat stored?
and:
Was the stored heat released too quickly?
If Input was low, you may need more stored energy.
If Output was high, you may need to conserve the stored heat for longer.
Sometimes both settings need adjustment.
Change settings gradually so that you can understand what effect each change has.
Don’t Change Everything at Once
Storage heaters respond over a long period.
If you change Input, you may not properly see the effect until after the next charging cycle and following day.
Therefore, changing several controls repeatedly can make the system harder to understand.
A better approach is:
- Make a small adjustment
- Allow the heater to charge
- Observe the following day
- Note when the room feels comfortable
- Note when the heater begins running out of useful heat
- Adjust again if necessary
After a few days, you can usually learn how the heater behaves in your particular home.
Modern Storage Heaters
Modern storage heaters can be much more sophisticated.
High-heat-retention models may include:
- Better insulation
- Electronic thermostats
- Programmable heating schedules
- Automatic charging
- Fans
- Improved heat-release control
- Digital displays
- Adaptive functions
Therefore, you may no longer manually decide exactly how much Input is required each night.
Instead, the heater can calculate how much energy to store based on factors such as the desired room temperature and heating schedule.
Automatic Charge Control
A modern storage heater may determine its own charging requirement.
Rather than asking you to predict tomorrow’s weather manually, the controls can calculate how much stored heat is likely to be needed.
This can reduce one of the major disadvantages of older storage heaters.
However, the heater still needs to be programmed correctly.
For example, it needs to know:
- Desired room temperature
- When the room should be warm
- Relevant operating schedule
Therefore, automatic does not mean no setup required.
Modern Storage Heaters Still Need the Right Tariff
Improved controls do not remove the importance of electricity prices.
The heater still needs electricity to charge.
Therefore, understand:
- When it charges
- What electricity rate applies
- Whether the tariff suits storage heating
- How any direct boost is charged
A sophisticated heater operating on an unsuitable tariff can still be expensive.
Smart Meters and Storage Heating
Smart meters can make electricity use easier to understand.
Your supplier app or in-home display may show increased consumption during storage-heater charging periods.
Over several days, you may be able to compare:
- Cold versus mild weather
- Overnight consumption
- Daytime consumption
- Boost use
- Changes after adjusting heating settings
This can help you understand whether your heating is operating as expected.
However, your smart meter normally records total household electricity consumption rather than identifying every individual heater.
Use the information to identify patterns.
Why Is My Overnight Electricity Use So High?
If you have storage heaters, high overnight electricity consumption may be completely expected.
That may be when the heaters are charging.
Your immersion heater may also be heating a hot-water cylinder during the same period.
Therefore, don’t judge consumption simply by seeing a large number overnight.
The more useful question is:
What did that electricity cost, and what was it used for?
If it was purchased at an appropriate off-peak rate and provided the next day’s heating and hot water, the pattern may be entirely intentional.
Why Is My Daytime Electricity Use High?
If you expected most heating to come from stored energy but daytime electricity use is high, investigate what is operating.
Possible causes include:
- Direct boost heating
- Immersion-heater boost
- Portable electric heaters
- Other household appliances
- A different heater configuration
Your smart-meter data can provide clues, although it will not necessarily identify the individual appliance responsible.
Should I Switch Storage Heaters Off in Summer?
If no space heating is required, there is generally little reason to deliberately charge traditional storage heaters simply to release unwanted heat into the property.
However, controls vary.
Follow the manufacturer’s instructions when changing seasonal settings.
Also remember that switching off storage heating does not necessarily switch off your hot-water system.
If your hot water also uses off-peak electricity, make sure you understand which controls operate which equipment.
Don’t Cover Storage Heaters
Storage heaters can become very hot internally.
Therefore, ventilation around them is important.
Do not:
- Cover them with clothes
- Place objects directly against ventilation openings
- Block grilles
- Use them to dry laundry unless the manufacturer specifically permits it
Also keep combustible materials at appropriate distances according to the manufacturer’s instructions.
Furniture and Curtains
Large furniture directly in front of a heater can restrict heat distribution.
Likewise, curtains hanging over or immediately against a heater may interfere with airflow and can present a safety concern.
Allow the heater to release heat into the room as intended.
This improves both comfort and safety.
When Might a Storage Heater Be Faulty?
Possible signs of a problem include:
- The heater never becomes warm after the charging period
- Only part of the heater warms
- Controls do not respond
- Electrical protection repeatedly trips
- There are unusual smells or signs of overheating
- The heater behaves very differently from similar heaters in the property
However, a heater being cool by evening does not automatically mean it is faulty.
First consider whether the stored heat has simply been used.
Likewise, a heater that is not very hot after a mild day may be behaving normally if a modern automatic control has deliberately reduced its charge.
Don’t Open or Repair a Storage Heater Yourself
Storage heaters contain mains electrical components and can store substantial amounts of heat.
Older units are also extremely heavy because of the internal storage blocks.
Therefore, internal repairs should be left to an appropriately competent professional.
Do not remove covers or attempt electrical repairs simply because the heater does not appear to be charging.
Start with the normal user controls and tariff arrangements.
A Simple Guide for Older Storage Heaters
For a traditional heater with manual Input and Output controls, remember:
If the room is not warm enough all day:
You may need more Input.
If the room is very warm in the morning but cold by evening:
The Output may be releasing heat too quickly.
If the heater is still extremely hot when you no longer need heat:
You may be storing more energy than necessary.
If the heater never warms after the off-peak period:
Check the controls, electricity supply and charging arrangement.
If Boost is used frequently:
Consider whether the heater is storing enough energy and whether the Output is being managed appropriately.
Also check what electricity rate applies to the boost.
The Most Important Rule
With a traditional storage heater, you have a limited amount of stored heat available between charging periods.
Therefore:
Input determines how much heat goes in.
Output determines how quickly that heat comes out.
If you store too little, you may run out.
If you release it too quickly, you may also run out.
And once the stored heat has gone, the heater cannot release heat that is no longer there.
That is why a traditional storage heater can be hot in the morning and cold in the evening without anything actually being wrong with it.
In Short
Storage heaters are designed to buy electricity at one time and provide heat later.
Traditional heaters store thermal energy during an off-peak charging period.
With older manually controlled models:
Input → controls the amount of stored heat
Output → controls the rate at which stored heat is released
If all the heat is released before the next charging period, the heater will go cold.
Therefore, using a traditional storage heater successfully means balancing how much heat you store with how quickly you use it.
Modern storage heaters make much of this easier through improved insulation, thermostats and automatic controls.
However, the same underlying principle remains:
Store enough heat → retain it until needed → release it at the right time.
Finally, always consider the heater alongside the electricity meter and tariff.
A storage heater is not just an appliance.
It is part of a system involving:
The heater + its controls + the meter + the electricity tariff + the way you use your home.
Understand all five, and storage heating becomes much easier to manage.
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