From §13-196-410 Residential buildings – Heat to be furnished:

Every family unit or rooming unit to which heat is furnished from a heating plant used in common for the purpose of heating the various rooms of the dwelling shall be supplied with heat from September 15th of each year to June 1st of the succeeding year so that the occupants of a family unit or rooming unit may secure, without such undue restriction of ventilation as to interfere with proper sanitary conditions, a minimum temperature of 68 degrees at 8:30 a.m. and thereafter until 10:30 p.m. and 66 degrees at 10:30 p.m. and thereafter until 8:30 a.m. averaged throughout the family unit or rooming unit.

If you are not receiving adequate heat per the Chicago Heat Ordinance, call 311.