Performed preventative maintenance on a Lenox standard gas furnace. Inspected all electrical components. Cleaned flame sensor, burners and burner compartment. Tested the amp draw for the blower and inducer motor. Both are operating within manufacturer specs. Customer has two return trunks that go into the furnace on both sides. Customer was unaware of the other one on the right side and that it had a filter. Customer replaced the left side filter (16x20x1). I replaced the filter he was unaware of on the right side (20x20x1). Customer recently had a duct cleaning performed By another company and they found insulation within the ductwork. Customer is concerned of indoor air quality. Inspected the duct work to make sure that there was no major holes for insulation to be sucked in. Found no damage to the ductwork within the crawlspace. Attached will be estimates for the two media filter cabinets as well as a Reme halo air purifier. System is operating properly at this time.