Abstract: A rotatable louver assembly (20) for a fan discharge duct (14). The louver assembly has at least two louver slats (21, 22) that are fixed in spatial relationship with respect to each other. A first or upper louver slat (21) has a shape that conforms generally to the shape of a first or upper wall (41) of the discharge duct. The second or lower louver slat (22) has a shape that conforms generally to the shape of a second or lower wall (42) of the discharge duct. The louver assembly has at least two positions. In one position the first louver slat is generally aligned with and spaced from the upper wall to define a generally constant cross-section low loss passageway therebetween for directing air horizontally. In another position the second louver slat is generally aligned with the lower wall to define a generally constant cross-section low loss passageway therebetween for directing the air generally vertically.