I just moved into an apartment in a very old building that has a heating system of unknown vintage. It appears to be forced air with vents on the first floor and one in the hallway on the second that blow air. The upstairs rooms have floor vents that open to the rooms below so rising hot air can heat those rooms. I have not been able to locate a return air vent. My question is how often the filters and duct work need to be cleaned. I tried out the system and found I could hardly breathe after a few minutes. I need to approach the property manager, but want to have my facts straight first. Thank you.