Exchangers can be less expensive and smaller if finned tubes are used. Fins make better use of the pressure drop available, because the length of travel in pure crossflow is low and the available flow area is large. This is advantageous in low-pressure gas or vapor applications where the pressure drop available is small. Finned tubes have been used in air coolers, shell-and-tube units, and longitudinal pipe exchangers. This chapter presents some facts about them.