Re: Oil? Coal?

There are a couple of differences between coal and wood fireboxes as well.
While either fuel can be used, fireboxes will work best with the boxes they were designed for. Coal fireboxes usually are sloped somewhat toward the front and the grates have somewhat more air space. There must also be a provision for shaking down the ashes. Wood fireboxes are built with level grates, often with solid pieces on the sides and ends to prevent cold air from entering around the edges of the fire. The ash mostly goes up the stack and what is left easily falls through the grates, so that grate shakers are not needed.

SVRR's Heisler #3 was built as a wood burner, but during it's time in Idaho coal grates were installed. I don't know how it did as a coal burner, but burned wood better after we installed 6" plates around the edges of the firebox.