The SHAMI_SV-2120_8" VENTILATING FAN Exhaust Fan Swift comes in two sizes, 6 and 8 inches. It is simple to install on glass in a circular opening from the inside and is supported by string. The back cover can be closed and operated. Circular opening size: 248–250 mm Delivery by air 5% ± 2200 Speed rpm 10% ± 384 Source of power number 22