Abstract: A heating furnace of convection type is provided for improving rising characteristics at an operation start-up time to stabilize conditions within the heating furnace in a shorter time and maintaining a uniform temperature in the furnace. The heating furnace comprises a conveyer unit for supporting an article to be heated and conveying the article through a heating chamber of a furnace body having an article inlet and outlet, a heating source provided in at least one of side and top portions of the furnace body such that the heating source is exposed to the interior of the heating chamber, an exhaust port formed in a lower portion of the heating chamber at a position displaced a predetermined distance from the heating source in the longitudinal direction of the furnace, the exhaust port being positioned below a lower end of the heated article, and an air inlet port associated with the heating source and provided below the exhaust port.

Abstract: A heating furnace comprises a horizontal body portion, a source of heat located at an intermediate portion of the body portion for forming hot gas which circulates in the body portion by natural convection, a gas discharge port formed in the wall of the body portion, a gas collecting hood connected to the lower end of an exhaust cylinder, and a horizontal conveyor for conveying an article to be heated through the furnace. The opposite ends of the body portion act as the inlet and outlet ports as well as gas discharge ports. In one embodiment, upper half portions of the inlet and outlet ports are covered by shielding plates. In another embodiment the opposite ends of the body portion are inclined downwardly to form the inlet and outlet ports near or below the bottom surface of the furnace. In still another modification, air curtains are formed at the inlet and outlet ports.