Indoor household gas heaters can be broadly categorized in one of two ways: flued or non-flued, or vented and unvented.
The first gas heater made use of the same principles of the Bunsen burner invented in the previous year. It was first commercialized by the English company Pettit and Smith in 1856. The flame heats the air locally. This heated air then spreads by convection, thus heating the whole room. Today the same principle applies with outdoor patio heaters or “mushroom heaters” which act as giant Bunsen burners.
Beginning in 1881 the burner’s flame was used to heat a structure made of asbestos, a design patented by Sigismund Leoni, a Britishengineer. Later, fire clay replaced the asbestos because it is easier to mould. Modern gas heaters still work this way although using other refractory material.