How Do Storage Heaters Work?
Charging overnight on Economy 7, storing heat in ceramic bricks, and releasing it gradually during the day.
The Basic Principle
A storage heater works a bit like a hot water bottle for a room, charged up in advance and then left to release warmth slowly. Three things happen in sequence:
- Charge overnight. Electric heating elements inside the unit heat a stack of dense ceramic bricks during the off-peak hours, when electricity is cheapest.
- Store the heat. Ceramic has a high thermal mass, meaning it can absorb a large amount of heat energy and hold onto it for many hours before cooling significantly. A well-insulated heater can stay warm for 12 to 24 hours after charging.
- Release through the day. Heat radiates directly from the casing and convects into the room as air passes over the hot bricks, warming the space without drawing any more electricity until the next charge cycle.
Because the bricks are doing the work of holding heat rather than the electricity supply itself, the heater doesn't need power flowing continuously to keep a room warm during the day, which is exactly what makes the overnight-charge, daytime-release pattern possible.
Economy 7 Tariffs
Storage heaters are built around the assumption that you're on an Economy 7 tariff, which gives roughly seven hours of noticeably cheaper electricity overnight in exchange for a slightly higher rate during the rest of the day.
- Off-peak hours (typical)
- 00:30–07:30, though exact times vary by supplier and region
- Off-peak rate
- Around 9p/kWh (2026)
- Peak rate (rest of day)
- Around 28p/kWh, higher than a standard single-rate tariff (around 24p/kWh)
The heater charges automatically during the off-peak window, controlled either by a simple mechanical time switch wired into the circuit or, increasingly, by a smart meter that recognises the tariff periods. You don't need to do anything manually for the charge to start and stop at the right time, though you do need to set how much charge each heater takes.
Old vs Modern Storage Heaters
Older storage heaters (roughly pre-2010):
- Thinner insulation around the bricks, so more heat leaks out overnight before it's actually needed
- A manual input dial where you estimate how much charge to take based on how cold you expect tomorrow to be, with no feedback if you guess wrong
- A manual output damper that adjusts how fast heat escapes, but with limited effect and no way to stop it once the bricks are hot
- Heat releases passively across the whole day whether the room needs it or not, which wastes energy in rooms that are empty during the day
Modern high-heat-retention storage heaters (2010 onwards):
- Thicker, better insulation that keeps 20–30% more of the charged heat available for when it's actually wanted
- Programmable timers that let you set different charge levels for weekdays and weekends, useful if the house is empty on working days
- Built-in thermostats that stop the fan or output once the room reaches the target temperature, cutting waste from overheating
- Fan-assisted output, so heat can be pushed into the room on demand rather than leaking out constantly
- Some models can top up charge slightly during the day if the weather turns colder than expected, within limits set to avoid peak-rate charging
Controls Explained
Input control sets how much electricity the heater draws overnight, which determines how much heat gets stored in the bricks. A higher setting means more electricity used and more heat available the next day. You adjust this yourself based on how cold tomorrow is likely to be, ideally checking a forecast rather than guessing.
Output control governs how quickly stored heat is released into the room. On older heaters this is a simple damper that opens or closes a vent, giving crude control over the release rate. On modern heaters, output is usually managed by a fan that pushes warm air out on demand, which means you can hold heat in reserve for the evening rather than losing it all by lunchtime.
Thermostat (fitted to most modern models) measures the room's actual temperature and stops the fan, or reduces output, once the target is reached. This is the single biggest difference between old and new heaters in terms of comfort and waste, since it prevents a room being needlessly overheated because the bricks still have charge left.
Why They're Common in Flats
Storage heaters remain widespread in UK flats, particularly those built before 2000, for a few practical reasons:
- Many blocks were never connected to mains gas, especially high-rise developments where running a gas supply to every flat was impractical or against fire regulations
- There's no space for a boiler, flue and radiator pipework in a small flat, and running pipes through shared structural floors is expensive and disruptive
- Upfront cost is low compared with retrofitting gas central heating, typically £300–£500 per heater against several thousand pounds for a full gas system
- Storage heaters have no moving parts to speak of and need no annual gas safety inspection, which suits landlords managing multiple units
The trade-off, covered in detail in our running cost guide, is that storage heaters cost more per kWh of heat delivered than gas, even at the cheaper Economy 7 rate.
Related Guides
Sources
- Energy Saving Trust, "Storage Heaters" guidance (mechanism, controls and Economy 7 explainer, 2026).
- Ofgem, "Default Tariff Cap" (June 2026: Economy 7 off-peak and peak rates).
- Citizens Advice, "Storage Heaters" (input and output control explainer, 2025).
- BEAMA, "Guide to Electric Heating" (old vs modern storage heater technology, 2024).
- Which?, "Storage Heaters: Are They Worth It?" (heat retention comparison, 2025).
Last reviewed: 2026-06-27