Storage Heater Controls: Input, Output and Smart Charging

A storage heater has two jobs to do with one store of heat: decide how much electricity to take overnight, and decide how fast to let that heat out during the day. On older heaters those two decisions sit with the household, through an input dial and an output dial. On modern high heat retention units the first decision is taken automatically, using sensors and a programmer, and the household is left with a thermostat setting and a routine.

The controls matter because the heat is bought at one price and used at another. Storage heaters store heat generated from cheaper nighttime rates acquired on Economy 7 or Economy 10 tariffs¹. Get the charge right and the day is covered from cheap units. Get it wrong in either direction and the household either runs out of heat by mid-afternoon or pays for stored heat it never uses.

What the controls do: input, output and the charge decision

A storage heater normally has at least two controls: one regulates how much electricity is used to determine how much heat is generated for storage, and the other controls how much heat is released⁶. Manual storage heaters consist of two main controls, input, which regulates the amount of heat that the heater stores, and output, which controls how fast heat is released⁷.

The input or charge control regulates the amount of heat that is stored up during the night. It is set higher in cold weather and turned down or off in warmer weather². On a manual heater the household sets the input dial to decide how much heat to store: higher input means hotter bricks and more heat for the next day¹. The higher the input, the more electricity the storage heater will use and the more heat it will store¹.

The output or boost control regulates the rate at which the stored heat is released. It is left on a low setting during the day and turned up in the evening if more heat is needed². Older heaters release heat continuously, and the output dial controls the flow; the higher the output setting, the quicker the heater releases its stored heat¹.

That is the whole control system on a traditional unit: one dial for the purchase, one for the spend. Everything a modern heater adds, sensors, programmers, apps, is an attempt to make the first decision without the household having to think about tomorrow's weather.

Input and output dials: how older manual controls work

Older storage heaters use input and output dials to control heat⁸. An input dial, sometimes known as charge, controls how much heat the heater stores as it charges overnight. An output dial controls how much heat the heater releases during the day¹. Some models add a third control, a boost setting, which is a different thing entirely and is covered below.

The practical difficulty with manual control is that the setting has to be made in advance, on a guess. Storage heaters need to charge the night before, and any changes to the input will not take effect until the next day⁹. A cold snap forecast for tomorrow has to be anticipated tonight, and a mild day means heat stored that will not be needed.

There is one consolation in the design. Most storage heaters will only charge up at night, so the input setting can be left without danger of using expensive day-rate electricity¹⁰. The charge circuit is the safeguard: the heater cannot draw peak-rate power through the input dial even if the dial is left high.

Manual storage heaters have been phased out and replaced by more efficient, automatic models³. That does not mean every manual heater in a UK home has gone, but it does mean replacements and new installations are automatic by default, and the dial-based routine described here is a legacy skill rather than a current design.

The overnight charge: how the off-peak circuit and meter control charging

Storage heaters charge during off-peak hours when electricity is cheaper, usually overnight¹. Night storage heaters are set to charge up at night¹¹. The heater itself does not decide when that window opens; the meter and the tariff do.

Economy 7 requires a special multi-rate meter to be installed at the home¹². The meter has two sets of numbers, one marked low, which means night, and normal, which refers to today¹³. The cheaper Economy 7 time period runs for a seven-hour period at some point between 11.00pm and 8.00am, and the regional network operator, the company responsible for physically supplying electricity to the property, defines the exact hours¹⁴. Some variations offer 8.5 or 10 hours¹⁵.

This is the part of the system a household has least control over. The charge window is a property of the supply, not the appliance, and it can shift by region. A heater that charges fully between midnight and 7am in one area may be working to different hours a few miles away.

The tariff behind the controls: Economy 7 and Economy 10 off-peak windows

Economy 7 is a time-of-use electricity tariff that charges two different prices for the electricity used, giving a set number of hours of cheap electricity through the night with daytime electricity charged at a higher peak rate¹⁶. It is a dual rate tariff with two distinct electricity rates⁸. For energy customers who have electric storage heaters, the Economy 7 tariff is an ideal option as they can be heated overnight and used to give off heat the following day¹³.

The economics depend on how much of the household's electricity lands in the cheap window. For Economy 7 to be economical, at least 40% of electricity should be used at night². A separate rule of thumb puts the threshold at more than 35% of electricity used at night to make Economy 7 cost-effective¹⁴. The two figures differ, so both are worth knowing: somewhere between roughly a third and two fifths of consumption needs to fall in the night window.

Economy 7 is only available for electricity-heated homes and not those with a gas supply¹⁷. In Scotland, Economy 7 meters are known as white meters, because the meters supplied by energy companies are white¹⁸.

Economy 10 works in the same way but offers 10 hours of low-cost electricity per night¹⁵. The Economy 10 tariff provides 10 set hours of cheaper off-peak electricity, and three of these hours are in the afternoon with seven overnight¹⁴. One description gives the split as three hours in the afternoon, two hours in the evening and five hours through the night². The off-peak times that fall under an Economy 10 tariff vary from supplier to supplier and region to region¹⁹.

Economy 10 has practical drawbacks. To get an Economy 10 tariff you must have an Economy 10 meter, and a supplier may charge a fee to install one as they are fairly uncommon¹⁹. Switching away may also carry a fee for a standard meter, and many price comparison sites cannot support comparisons for Economy 10 meters¹⁹. There simply are not many Economy 10 suppliers available¹⁹.

High heat retention heaters: automated and digital controls

High heat retention storage heaters have automated controls, are well insulated and retain more heat than other storage heaters⁸. They are described as the most efficient type of night storage heater⁵. More modern storage heaters use digital controls, while older heaters have manual controls¹.

The defining feature is that the charge decision moves from the household to the heater. Modern heaters use sensors and smart controls to store just the right amount of heat¹. These models achieve even better heat retention and are able to estimate the next day's heating demand based on user heating habits and climatic conditions, so input settings need no adjustment¹⁰. The automatic charge control works out how much electricity it needs to store to meet the programme and only uses the amount of electrical charge it needs⁸. To do this it looks at the temperatures inside and outside, as well as how much heat was needed the previous day¹.

Modern storage heaters generally come with improved heating controls, including an automatic charge control, thermostat and programmer, and have higher heat retention, meaning they hold heat for longer than older units⁸. Many also feature a thermostat and timer through a programmer or mobile app, often with fan-assisted heat release and better insulation¹⁰. Depending on the model, it may be possible to control the storage heater with an app¹.

Automatic charge control is not optional decoration on a new installation. Approved Document L states that automatic control of input charge should be provided, and the same requirement appears in the Welsh consultation version of the document²⁰. A new electric storage heater is expected to manage its own charge.

Thermostats, programmers and automatic charge control on modern heaters

Once set, digital electric storage heater controls are easier to run than manual controls, because they automatically store enough heat for the set routine¹. The household's job shifts from judging the weather to setting a routine and a temperature.

The thermostat lets the household set the temperature the storage heater should heat the room to¹. The programmer carries the schedule. The automatic charge control then regulates how much energy is used by storing more or less heat at night¹. If the routine is accurate, the charge follows it.

The Dimplex Quantum is the model most often described in UK guidance on this generation of controls. It has thermostats and a digital programmer, making it much more responsive to household needs²¹. Its boost option does not use heat already stored in the heater but uses the expensive rate of electricity to generate heat²¹.

Should the boost be used during the day?

The boost is the one control that spends money rather than moving it. Some models have a boost function that tops up the electric storage heater by getting electricity from the grid as needed¹. Integrated night storage heaters include a boost function for when stored heat runs out, and it uses more expensive on-peak electricity⁵. On older night storage heaters the boost setting does not use cheap-rate stored heat, it uses expensive daytime electricity¹⁰.

The distinction matters because the boost feels like the same appliance doing the same job. It is not. The stored heat was bought overnight at the off-peak rate; the boost is bought at the moment of use at the peak rate. It is a fallback for when the stored heat has run out, not a way to extend the day's heating cheaply.

Why a storage heater runs out of heat in the afternoon

Storage heaters can often leave a home very warm in the morning and struggle to stay warm in the evening²². The cause is usually the output setting rather than a fault. Older heaters release heat continuously, and the output dial controls the flow, so a high output setting empties the store early¹.

Traditional night storage heaters require the household to manually set both how much heat to store overnight and when and how much to release during the day⁵. Two guesses, both made in advance, both capable of being wrong in the same direction. The output control is normally set to low unless extra heat is needed, and turned up in the evening².

The fix on a manual heater is to hold the output down through the day and release heat in the evening when the house is occupied. On an automatic heater the same logic is built into the programme. High heat retention models are well insulated and hold heat for longer, which reduces the problem but does not remove the need for a sensible routine⁸.

Getting the settings right through the seasons

The input setting is the seasonal control. It is set depending on the expected next day temperature, higher in cold weather and turned down or off in warmer weather². That is the whole seasonal adjustment on a manual heater: charge more before a cold day, charge less before a mild one.

The difficulty is that the setting is made the night before and any change to the input will not take effect until the next day⁹. Shoulder seasons, when a cold morning follows a mild afternoon, are where manual control is weakest. Automatic charge control removes the guesswork by reading indoor and outdoor temperatures and the previous day's demand¹.

There is a wider point about controls generally. It is important to get the heating controls right before trying to change the flow temperature²³. The same principle applies here: the charge and release settings are the foundation, and no amount of fiddling with anything else compensates for a store that is charged wrongly.

Charging with solar: a daytime alternative to off-peak charging

The standard storage heater model buys heat at night and spends it by day. A household with solar panels can invert that. Solar panel electricity could be used to charge storage heaters during the day so there is still warmth in the evening³.

The mechanism is the same store of bricks, filled at a different time. Solar panels are used to charge up an on-site battery storage system²⁴, and the same daytime generation can feed the heater's charge circuit where the installation allows it. The attraction is obvious: the heat is bought at nothing rather than at the off-peak rate.

The limits are equally obvious. Solar output peaks in summer, when heating demand is lowest, and falls away in winter, when the storage heater needs its longest charge. A solar-charged storage heater is a supplement to the off-peak charge, not a replacement for it, and it depends on the household having panels and a suitable circuit arrangement.

What the controls mean for energy independence

Storage heater controls sit at an unusual point in a home's energy arrangements. The heat is generated on site, from electricity, and stored in the fabric of the appliance. There is no boiler, no gas connection, no flue and no cylinder. A household with storage heaters and its own generation has removed the fuel supply from the equation entirely.

What remains is the tariff and the meter. The cheap charge depends on an off-peak window defined by the regional network operator and delivered through a specialist meter¹⁴. The controls cannot create that window; they can only use it well. A household on a single-rate tariff has the same heater and the same dials, but every unit of stored heat costs the daytime price.

The second dependence is on the manufacturer's control system. Automatic charge control, app control and smart charging all rely on the maker's hardware and, where an app is involved, on the maker's service continuing. A manual heater with two dials has no such dependency, which is one reason the older units keep working long after their controls have been superseded.