For the purpose of determining whether or not the temperature in any such room or apartment is in accordance with the provisions of the preceding section, temperature readings shall be made only by an inspector under the direction of the county health department by means of a standard fahrenheit thermometer approved by the health officer in not less than two (2) separate rooms in such apartment, or if the apartment consists of only one room, then in two (2) opposite parts of the room as near the extremes as practicable, such thermometer to be placed at a point not less than four feet (4') nor more than six feet (6') away from any door or window leading to the outer air nor more than four feet (4') above the floor. Failure to furnish the heat required in the preceding section shall not constitute an offense where it is due to a breakdown of the heating plant, if diligence is used to have such plant repaired (unless such breakdown has been caused by the violation of an existing ordinance relating to the operation of heating plants), nor where it is due to strikes, to general shortage of fuel, to any act of the tenant who makes the complaint, or to any cause beyond the owner's control, unless written notice of such failure to furnish the heat required shall first have been given to the owner or agent of the building by registered mail, and the temperature readings herein provided for shall not be made until after the delivery of such registered letter to the addressee thereof. (1965 Code §16-2.02)