The flue is, of course, a very important factor. Its cross section should be at least one-tenth of the area of the front opening of the fireplace. A flue having an area greater than one-tenth of the area of the finished opening is not objectionable, but one having less dooms the fireplace to unsuccessful operation.
The flue should be lined with a fireclay flue lining properly bonded together and to the masonry of the chimney. The area of the flue should be maintained for the entire height of the chimney and not contracted at the top. All turns and bends should be as gradual as possible, with no angle more than 30 degrees from the vertical. And every fireplace should have its own flue. Never connect any other heating apparatus to a fireplace flue.
The chimney should project at least three feet above any flat roof and two feet above the ridge of a hiproof.
In the table below are shown all the essential dimensions needed in the construction of a successful fireplace. The dimensions are worked out on a basis of the width of the fireplace opening. Slight variations in this dimension will alter the other dimensions somewhat, but the proportions may be easily worked out.
