"[T]he height to which the new back and covings ought to be carried... will depend not only on the height of the mantle, but also, and more especially, on the height of the breast of the Chimney, or of that part of the Chimney where the breast ends and the upright canal begins.—The back and covings must rise a few inches, five or six... higher than this part, otherwise the throat of the Chimney will not be properly formed;—but I know of no advantages that would be gained by carrying them up still higher."