Every person leasing or renting to another, space in any building under an agreement, express or implied, which includes the furnishing of heat by such person, shall at any time that the outside temperature is below 68 degrees Fahrenheit furnish heat in such space so leased or rented, heat sufficient to maintain a temperature of not less than 68 degrees Fahrenheit at a height of 3 feet from the floor, between the hours of 7:00 a.m. and 10:30 p.m. of each day; except in buildings which are regularly and customarily occupied only during the day by the lessees or tenants thereof, said minimum heat shall be furnished between the hours of 8:00 a.m. and 5:30 p.m. of each day except Sundays, and in buildings occupied at irregular intervals, the minimum heat shall be furnished during the period of occupancy.