Re: Questions about operating the 493 as an oil burner

Regarding the tiny door to the firebox: The correct air/fuel ratio is important to the efficient combustion of the fuel oil. Most air is introduced at the bottom of the firebox such that it will mix with the fuel and support combustion. However there are times when the introduction of air over the top of the flame is advantageous. Air can be introduced in large volumes through the butterfly (if so equipped) in the door and extra air or a fine adjustment can be had by opening and closing the sanding port, a round opening in the firebox door. Introduction of air via the door is called introduction of secondary air. The air enters the firebox above the flame. The air aids in combustion (typically of carbon monoxide which burns to carbon dioxide and provides a significant heat source) and also helps cool the crown sheet (not much nor injuriously but sufficient to improve the operation of the boiler). It requires an astute fireman to know when to change the secondary air and recognize the change.