Heat exchanger

A heat exchanger of the fin and tube type where the tubes are spaced apart with confronting surfaces that are provided with a plurality of heat exchange fins attached to these confronting surfaces in sets of fins on each tube in which the sets of fins have portions such as the peaks of undulating fins adjacent to but spaced from each other to permit flow of a heat exchange second fluid over the fins and between the spaced portions for substantially unrestricted flow of the second fluid over the fins and through the resulting fin space, thereby providing substantially unrestricted flow of the second fluid with improved heat transfer.