If I may ask a dumb question, coming from a country where residential central heating is not common, (certainly not this oil fired kind), what stops the flames and/or carbon monoxide going into the ducts? Is there some kind of heat exchanger? If so, what if it leaks?
In Australia, oil heaters were popular from the 1960's up until the mid 70's, but they were installed in the living room, like a gas heater or enclosed fire place. The oil seemed to be more like kerosene, and I discovered it burnt just as well in hurricane lamps. There was a tank mounted on the side of the house that would need filling about once a year. Used to be a common sight around suburbia to see an oil truck parked outside someone's house with its black hose trailing down the driveway.
We had a late 60's model in the first house I lived in, which burst into flames in the middle of the night. It had a burner much like a gas ring, and you opened the door to light it with a match. It was replaced by a more modern version that looked more like a gas heater, with ceramic panels to radiate the heat from the burner underneath. Ignition was from a heating element; after a few minutes it would suddenly burst into flame.
