Which side is a hot shot furnace's "front?" The end into which cannonballs are deposited, with the chimney above, or the end from whence the reason for that edifice's being is issued, in the form of those same cannonballs, heated red-hot? The end into which the balls are entered seems like the furnace's front to me, in that it has steps to assist the soldier in his mission (as the opening on that end is naturally higher than the other, as the balls roll down to be removed once ready for firing)...

Regardless, as we approach Fort Niagara's hot shot furnace, we see the sliding iron doors that would have been opened with a shovel or similar tool, exposing the channel into which a ball would be deposited. Rest assured that in the 21st century, these doors' sliding days are long over.