Every dwelling unit to which heat is furnished from a heating plant used in common for the purpose of heating the building shall be supplied with heat without such undue restriction of ventilation as to interfere with proper sanitary conditions, to provide a minimum temperature of sixty five degrees Fahrenheit (65°F) at six thirty o'clock (6:30) A.M., and seventy degrees Fahrenheit (70°F) at eight thirty o'clock (8:30) A.M. and thereafter until ten thirty o'clock (10:30) P.M., and a minimum temperature of sixty degrees Fahrenheit (60°F) thereafter until six thirty o'clock (6:30) A.M. average through the dwelling unit. It shall be unlawful in any dwelling or building heated by a central forced hot air system to run a heating duct or cold air return to or from a garage whether attached or unattached. (1975 Code § 11.04)