Abstract: An air heating device includes two closed conduits, one conduit for the flow of the air supply to a combustion furnace and the other for the flow of exhaust gas from a combustion furnace to a flue. The conduits pass through and around each other multiple times in an interweaving pattern such that the entirety of either conduit is almost completely surrounded by the other conduit, to maximize contact area and thermal energy transfer between the conduits relative to the device size and no use of small tubes or passageways. The shapes and pattern of the two conduits resembling the appearance of a sine wave and cosine wave drawn on the same x axis.

Abstract: Device for heating air during the duty cycle of a heating boiler fired in particular by solid fuel or biomass, composed of a conduit for supplying air to the furnace and a conduit for outflow the exhaust gas from the heating boiler into the flue. The device has the closed exhaust gas conduit (2) which over the length of its connection with the flue (8) is shaped resembling a cosine curve with advantageously vertical exhaust gas conduits (4) adhered to the vertical air conduits (11) which over the length of the air conduit (3) have a shape resembling a sine curve, and on the last vertical conduit (5), where the end section (7) of the exhaust gas conduit (2) is guided to the flue (8), there is a pumping fan (6).