The Riverstone RSI General Purpose Greenhouse and Small Building Exhaust Fan System is designed to fit all structures. The general design is for low-profile structures that are in need of air. This exhaust fan system is proudly made in the USA and truly designed to fit all structures, but the purchaser needs to be able to retrofit the exhaust system to their own structure since each structure and building materials are different. There are two ways this general purpose exhaust fan can be mounted, from the outside or from the inside. If mounting from the outside a hole in the wall would need to be cut to allow for the fan and interior cage to fit through the wall. The rough dimension is 17 inches x 17 inches. Use fasteners (not included) to fasten the fan to the wall by drilling through the framework and caulking the framework to make it watertight. The fan structure is now 100% enclosed in the building and the louvers are on the outside of the structure. If mounting from the inside, a hole in the wall would need to be cut so that the louvers will be able to open and close freely. This dimension is 16-1/4 inches x 16-1/4 inches. Slide it in the opening from the inside out. The exterior lip around the louvers acts to finish off the appearance from the outside. Seal with caulking and fasten the fan to the wall (fasteners not included).Note: This product may require up to 7 additional days for order processing prior to shipping