Rev. Rul. 55-146

An electric belt-driven fan which is designed for use as an exhaust or intake ventilating fan to be operated as an independent unit and which has a blade diameter of less than 40 inches, is considered to be of the `household type,' unless it has other features of construction by which it may be identified definitely as being primarily adapted for commercial or industrial use. Therefore, such fans are subject to the manufacturers' excise tax imposed by section 3406(a)(3) of the Internal Revenue Code of 1939