Cutaway illustration of a storage heater. A storage heater is an electrical heater which stores heat energy at night or when electricity is cheaper, and releases the heat during the day as required. Storage heaters contain a heat storage medium such as concrete blocks (grey), with embedded electrical heating elements (red lines). Cool air (blue arrow) is drawn into the bottom of the heater, and warmed by the heated blocks. The warmed air rises (red arrow), and the stored heat is given off continuously through thermal radiation and convection.