Abstract: A heat exchanger for use with a pottery kiln or the like includes a plurality of tubes for carrying air aligned by and arrayed in groups in a vertical array from the cool end to the hot end of the flue of the kiln. Connecting passageways are provided vertically between successive groups of tubes, for directing air from each group of tubes through the next hotter group, to heat the air gradually and in stages as it passes therethrough. As many sets of progressively hotter tubes may be used as required for raising the air therein to a desired temperature. Also, the number and size of tubes may vary overall as well as from group to group, according to the size of kiln and temperature to which the air is to be raised. The final group of tubes is provided with a connection to the combustion chamber of the kiln for mixing therein with fuel to provide flame to the firing chamber thereof.