Chilly Aprtments in winter

[Peter Morgan]

Hello,

I recently closed on a triplex and the apartments feels very chilly in winter weather proofing with a plastic cover sealing the windows  mitigated the issue little bit but I would like to get to the root of cause since even when thermostat is set at 80 it feels chilly,especially my lower two units are very cold despite a centralized ac system.Unfortunately I couldn't catch this during inspections since it was warmer weather around that time.I am now dealing with higher utility bills who are some professionals that I can get in touch with for solid weather proofing ?appreciate your feedback