"[T]he so-called Rumford stove or fireplace... contracted the area of the fire-chamber, and gave the sides an angle of 135° with the back, or, which is the same thing, of 45° with the front of the fireplace, in order, as he said, to reflect the greatest possible amount of heat into the room. He considered the best proportions for the chimney recess to be when the width of the back was equal to the depth from front to back, and the width of the front or opening between the jambs three times the width of the back. These proportions are used today, and are undoubtedly the best. He objected to the use of iron for these surfaces on account of its great heat-conducting power, which wasted the heat and cooled off the fire; but advocated some non-conducting substance, such as fire-clay. He also objected to circular covings, on the ground that they produced eddies or currents, which would be likely to cause the chimney to smoke."