Oil burning furnaces have the burner mostly on the exterior of the furnace due to its size. The blast tube goes into the heat exchanger where a mist of fuel oil is sprayed from a hose that goes to the tip of the blast tube called the nozzle. The nozzle contains electrodes which ignite the mist of fuel oil. The oil burner has a motor on it that is side mounted. This pumps oil into the nozzle as well as operates the fan that blows air across the flame and moves the air through the heat exchanger and through the exhaust system. One common issue with oil burners is clogged openings of the fan housing. Make sure these are free of debris, because the fan needs the air circulation to keep the brushes from overheating. If the furnace is calling for heat and the burner is not igniting, the ignition transformer that sends an electrical charge to the electrodes in the nozzle may be bad. This is located on the top of the burner. If it is extremely hot or loose, this may need to be replaced.
The barometric damper is a damper with a small weight on it that is normally closed when the furnace is off. When the furnace kicks on, the damper opens to suck in extra air to aid in the exhaust process. This damper is very important to prevent carbon monoxide buildup inside the home. Barometric dampers can get stuck open once in a while. Simply move it back and forth a few times to loosen up the damper.
Even though all furnaces have an area where you can inspect the heat exchanger, none are like an oil furnace. Because the heat exchanger get so hot, the inspection port is actually a metal cover that simply slides up, or is a peep port, meaning that there is a round metal piece that covers the port and has a screw in the top. To open the port, simply push it to the side. This is not recommended when the furnace is going, because flames and sparks can shoot out of the inspection port.