A range hood, comprising: a housing defining a first outer air vent and a second outer air vent; a volute casing disposed within the housing, and comprising a volute casing body having a bottom plate, a top plate and a side encasing plate disposed between the bottom plate and the top plate, the volute casing body defining an outer air outlet communicated with the first outer air vent and the second outer air vent, and an opening direction of the outer air outlet being orthogonal to that of the second outer air vent; a fan wheel disposed within the volute casing body; an outer switching cover plate disposed on one of the volute casing and the housing and movable between a first position, in which the first outer air vent is opened by the outer switching cover plate and the second outer air vent is closed by the outer switching cover plate, and a second position, in which the first outer air vent is closed by the outer switching cover plate and the second outer air vent is opened by the outer switching cover plate, an angle α between the outer switching cover plate in the second position and the opening direction of the second outer air vent being greater than 0 degree and less than 90 degrees; and whereby the range hood further comprises an outer air vent seal-plate, wherein the housing defines an inner air vent, the volute casing body defines an inner air outlet communicated with the inner air vent, the volute casing further comprises an inner switching cover plate movable between an opened position, in which the inner air outlet is opened by the inner switching cover plate, and a closed position, in which the inner air outlet is closed by the inner switching cover plate, in which the outer air vent seal-plate seals an opened one of the first outer air vent and the second outer air vent in the opened position. a housing defining a first outer air vent and a second outer air vent; a volute casing disposed within the housing, and comprising a volute casing body having a bottom plate, a top plate and a side encasing plate disposed between the bottom plate and the top plate, the volute casing body defining an outer air outlet communicated with the first outer air vent and the second outer air vent, and an opening direction of the outer air outlet being orthogonal to that of the second outer air vent; a fan wheel disposed within the volute casing body; an outer switching cover plate disposed on one of the volute casing and the housing and movable between a first position, in which the first outer air vent is opened by the outer switching cover plate and the second outer air vent is closed by the outer switching cover plate, and a second position, in which the first outer air vent is closed by the outer switching cover plate and the second outer air vent is opened by the outer switching cover plate, an angle α between the outer switching cover plate in the second position and the opening direction of the second outer air vent being greater than 0 degree and less than 90 degrees; and whereby the range hood further comprises an outer air vent seal-plate, wherein the housing defines an inner air vent, the volute casing body defines an inner air outlet communicated with the inner air vent, the volute casing further comprises an inner switching cover plate movable between an opened position, in which the inner air outlet is opened by the inner switching cover plate, and a closed position, in which the inner air outlet is closed by the inner switching cover plate, in which the outer air vent seal-plate seals an opened one of the first outer air vent and the second outer air vent in the opened position.