A rack of electronic equipment is convection cooled. Each unit in the rack has oblique cooling fins oriented in a same direction, to cause heated air to flow to a hot air pathway by a chimney effect, and to draw surrounding air along a cool air pathway to each of the units. A preferred unit has two housing sections thermally insulated from each other. Each housing section has its cooling fins on a side surface, some of the fins being aligned with fins on the other section, so that cooling air flows first over the cooler section and then over the hotter section. The cooler section is arranged for enhanced heat transfer from a heat sensitive element, and heat liberating units are heat sinked to the hotter section.