A damper box includes a curved wall, an outlet, a side wall, and filter and a damper. The curved wall has an outside surface, an inside surface, and a separator sandwiched between an outside air inlet and a recirculated air inlet. The side wall is disposed between the recirculated air inlet and the outlet. The filter has a curvature matching the curved wall and covering the outside surface of the curved wall. The damper has an axis of rotation adjacent to and in alignment with the separator. The damper has a first face and a trailing edge. The first face is curved and configured to mate with a curved frame disposed about the outside air inlet. The trailing edge is configured to mate with the side wall. A ratio of outside air to recirculated air is modulated in response to the damper being rotated.