The owner, operator or agent in charge of a dwelling structure, who rents or leases any dwelling unit therein under an agreement, express or implied, to supply or furnish heat to the occupants thereof, shall supply heat adequate to maintain an inside temperature of not less than sixty-eight degrees Fahrenheit in all habitable rooms, bathrooms, water closet compartments and kitchens whenever the outside temperature falls below sixty degrees Fahrenheit. Such inside temperature shall be measured in the approximate center of each room, approximately three feet above the floor. The provisions of this section shall not apply where the failure to meet minimum standards is caused by a general shortage of fuel, negligent or malicious act of the occupant or any cause beyond the control of the owner or occupant.