The inventive air heater comprises a housing (1) with a lining (2), a nozzle (3), a dome (5) with a prechamber (6), which is coaxially positioned in the top part thereof and is provided with a housing (7) and a lining (8) provided with an independent support (9) on the housing (7). Gas (11) and air (12) channels are made in the side vertical wall of the prechamber (10) lining and are connected to internal manifolds (14,15) and to gas (16) and air (17) supplying sleeve fittings. The channels of the lower manifold (15) are arranged in the top part thereof and are upwardly oriented at and angle of 15-30° with respect to a horizontal plane. The channels of the top manifold (14) are arranged in the lower part thereof and are downwardly oriented at an angle of 15-30° to a horizontal plane. The projections of all the channels on a horizontal plane form an angle of 15-45° to the projections of the prechamber radii, passing over the centers of the outlet sections of the channels (11, 12), on a horizontal plane. The use of the invention makes it possible to reduce operation costs and to improve gas burning.