A cased vertical evaporator coil is used with furnaces in the upflow or downflow position. The coils have physical dimensions to correspond to the various widths of Goodman furnaces available on our website, and are designed to fit correctly with the furnace. Typically a cased coil would be selected when installing a new furnace at the same time. If you are adding air conditioning (or a heat pump) to an existing furnace, then an uncased coil is best.