Regenerative heating systems

A regenerative heating system comprising two heat regenerators of the type having a bed of heat absorbing material and which are operable so that while one is being heated by waste gas the other is heating air for the combustion of a gaseous fuel, each regenerator having a first end serving either as an inlet for waste gas or as an outlet for combusted fuel and a second opposite end serving either as an outlet for waste gas or as an inlet for air, a common chamber lying between said first end of each regenerator and said bed and through which in use air and waste gas flow in opposite directions by way of their respective regenerators, means being provided to inject gaseous fuel into the chamber and each regenerator being provided internally with means serving in use to promote a pressure differential between the regenerators such that the pressure in the regenerator through which the air is passing is lower than the pressure in the regenerator through which the waste gas is passing so that the fuel is caused to be drawn from the chamber towards the air for admixture therewith for subsequent combustion.