After having a reliable oil burner for nearly 30 years, it was recommended to me last year to have a new one installed. I agreed because the blower was making a strange sound and my hvac tech said that, due to age, the blower would be difficult/ impossible to replace. Not only that but there was a strange smell coming from the ducts every time the heater was running. It's hard for me to describe since I don't have a good nose, but all I can say is that I could hardly stand the smell. I wouldn't say it was a soot smell exactly- more like "rotten" soot is the best way I could describe it. I figured a new oil burner installation would cure this. Before the cold set in this year, I had a new unit installed. Everything was replaced with new except my heater ducts. The heater runs great and is much quieter than my old unit, but the same strange smell has persisted and it has not become less over time. I have concerns about breathing whatever this is and I am posting here looking for solutions to cure it. Any idea what could be causing it and how do I get rid of the odor? As long as the furnace isn't running, I don't smell anything but the minute air starts coming from the vents, the odor is nearly overwhelming.