FIG. 1 is a perspective view of the housing for a box fan. FIG. 2 is a top view of the housing for a box fan, the bottom view being substantially identical thereto. FIG. 3 is a front view of the housing for a box fan, the rear view being substantially identical thereto. FIG. 4 is a side view of the housing for a box fan, the opposite side view being substantially identical thereof; and, FIG. 5 is a fragmentary cross-sectional view taken along line 5—5 of FIG. 1. The broken-line showing of environmental structure in FIGS. 1-4 is for illustrative purposes only and forms no part of the claimed design.