Abstract: This invention combines specific new and novel equipment with the equipment of a conventional combustion system for the use of liquid fuel oil to create a new system which converts the liquid fuel into gas and operates as a gas burner rather than as a liquid oil burner. The new and novel equipment thermally cracks liquid hydrocarbons into gaseous hydrocarbons which have substantially lower molecular weights than the liquids from which they were cracked. In the system the burner apparatus itself is modified to burn gas rather than liquid. In this new system the fuel burned does not consist of vapors of the liquids supplied to it but instead operates on the products of decomposition derived from the liquids.