Oil is nasty smelly *hit. My step mother in law called me last week to ask me about her furnace and I told her "I don't know nothing about no oil furnaces".
It's a simple rule of physics. The harder something is to burn, the more heat you will get out of it when you do burn it. In a wood stove you will get more heat out of the more dense green wood than the seasoned dry wood if you can maintain the fire hot enough to get it to burn. Larger oil consumers will use higher number fuel oils not only because less refining = lower cost per gallon but also because there are a few more BTU's. This is how it was explained to me many years ago in school. I'm sure if I'm wrong, someone will only be too happy to point it out.
In downtown Richmond there was a closed department store called Thalhimers. The boiler room was about 30 feet below ground and they had two coal boilers. The guy that bought the building had us convert the boiler to gas. Hanging all that 3" gas line must have been fun. I luckily was assigned elsewhere. They had to shovel out about 1500 lbs. of coal just to get started. There was a locker room with showers right at the entrance to the boiler room so the boiler guys could shower before leaving for the day. No thanks!