Abstract: A heat regenerator for use in heating an enclosure such as a furnace.The heat regenerator 51 is detachable at one end from a burner B and at its other end from a reversing valve 58. The regenerator 51 comprises two axially engaging portions 56 and 57, the front portion 56 comprising a cylindrical heat storage bed 59 and a surrounding annular layer 60 of a ceramic fibre insulation material. The rear portion 57 comprises a cylindrical body of refractory having a bore 61 forming a bottle-neck type passage tapering towards the valve 58. The heat storage bed 59 comprises a monolithic refractory block through which a multiplicity of axially aligned gas-carrying channels 65 extends. These channels 65 convey combustion products from the burner portion 52 to the regenerator portion 56 in one mode of operation where the bed is extracting heat from the products for storage.