No person shall sell or offer for sale at retail in the city any heating appliance constructed to burn gas or oil fuel, unless such heating appliance bears the seal or other indication of approval of the American Gas Association or Underwriters’ Laboratories, Inc. or is of a type and construction approved by the Building Department as meeting recognized safety standards as promulgated by said American Gas Association or Underwriters’ Laboratories, Inc.
(`78 Code, § 5.22.010.)