Electric heater utilizing a pourable heat storage bulk

A storage heater for heating a gaseous heat extraction medium, the heater comprising:

• a container having walls formed of a heat resistant material;
• at least one guide duct, in the form of a tube extending through the container, for carrying gaseous heat extraction medium;
• a thermal storage medium within the container, means associated with the container for supplying heat to the storage medium, the medium comprising heavy metal-bearing minerals and being in the form of a pourable heavy metal-bearing minerals and being in the form of a pourable bulk of particulate solids and being suitable for directly contacting air to be heated for places of human habitation;
• the product of the specific heat of the solid and the bulk density of the pourable bulk being at least 0.7 kcal/.degree. C dm.sup.3, the specific heat of the solid being at least 0.12 kcal/.degree. C kgf and the bulk density of the pourable bulk being at least 2.5 kgf/dm.sup.3.