Oil burning devices use flames, as do other types of heaters. These flames can be changed by making simple adjustments to the air intake on the burner itself. With the right knowledge, the air adjustments can be made at home. However, because it does involve a flame, it is important to consider your level of experience when making this sort of repair. If any concerns or questions arise, consult a professional immediately.
Remove the cover on the air intake valve, and check to see if it is clean. Dirt can reduce the amount of air that is flowing through the valve. Clean the air intake with a soft cloth or cotton swabs if any dirt or other contaminants are present.
Check the amount of soot that has accumulated from the burner. An increased amount of soot will be generated if the oil burner is receiving low air flow. The amount of carbon monoxide produced will also increase.
Find the air intake on the fan, which should be located on the left side of the burner. Adjust the squirrel cage baffles by loosening the screw that holds them to the heating unit. The baffles will be on left side of the burner near the pump. Slide the collar next to the baffles to the left or right. Each direction will adjust the amount of air moving through the heater, either increasing it or decreasing it.
Look at the flame colour on the oil burner as the collar is being moved. This will indicate if there is a lack of air. A flame that is dark yellow indicates less air. A flame that is receiving the right mixture of air should have a white, chrome or blue colour. Depending on the brand of oil burner, the flame could also appear light yellow. Refer to the owner's manual for specifics on the burner's flame colour. Make small adjustments while moving the collar until the appropriate flame colour is reached.
Have the user's manual readily available for any specific questions related to your specific model of oil burner. Make adjustments with the burner running. This will show immediate results as to what the air flow is doing to the flame.
If you do not have experience with adjusting oil burners, hire a professional.