Nothing in the regulations contained in this Chapter shall prohibit the installation of other types of permanently placed electrical heat‑generating and emission units not presently covered herein when such units are approved by the Underwriters’ Laboratories, Inc., and installed in a manner approved by such Laboratories providing they meet the general provisions of this Chapter and further that a separate disconnect shall be provided in each heated space, except that no individual thermostatic control shall switch any combination of heaters totaling more than 7 kilowatts.