A strong chemical odor emanates from my air vents, whether the heater is on or not. It is strongest in the master bedroom. Even after having the ducts professionally cleaned, I can still smell it. The duct cleaner says it smells like "a bottle of vitamin pills". Sometimes it is there, sometimes it isn't. I sealed off the vents to block out the smell. The furnace inspector says it is from the oils on the heat exchanger which is coated to preserve it. I have a CO detector in my home and it hasn't gone off. My question is if it is really from the heat exchanger, why don't the vents close to the furnace smell as strongly as the vents far away from the furnace (like my bedroom)? Is there anything else at all as to what this smell could be? Thanks.