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These and other objects are accomplished by a method to heat a formation, the formation lying below a Surface of the earth, the method including the Steps of: providing a wellbore within the formation to be heated, the Wellbore comprising a casing within the formation to be heated, a tubular defining, in the inside of the tubular, a flowpath for hot gases from the Surface to a point in the wellbore near the bottom of the formation to be heated, and a volume between the tubular and the casing providing a flowpath for hot gases from near the bottom of the formation to be heated to the top of the formation to be heated, wherein the flowpaths are in communication with each other near the bottom of the formation to be heated and the volume between the casing and the tubular at the top of the forma tion to be heated is in communication with a point above the Surface, and insulation for a portion of the length of the wellbore …