Show proper design helps chimney remove smoke shape size of flue control I 1 it is curious that so many fireplaces smoke when it is so simple to build one that dont the recipe according to an expert in the washington post is about as follows determine the size of opening desired S and then select a flue lining that has an area equal to at least 10 per cent of that opening use either a square or a round flue preferably a round one as that is the more efficient do not use rectangular flues unless absolutely necessary and in that case increase the size so that the area will equal at least 12 per cent of the opening build the fireplace with a depth of between 18 and 24 inches more than that depth robs the fireplace of a good deal of its heating efficiency install a cast iron damper for the full width of the opening this should be set so that the curving back of the fireplace makes a continuous line with the back of the damper opening above the damper at the back flush with the top edge of the opening build a horizontal smoke shelf about eight inches deep and for the full width of the opening also above the damper build a smoke charn cham ber with the front rising as a continuation of the front piece of the damper opening and the back rising perpendicular to the smoke shelf the sides should slope up at an angle of about 60 degrees with the horizontal this smoke chamber must be perfectly symmetrical and the first tile of the hue flue lining must start at its apex directly over the center of the fireplace this first tile must be perpendicular but succeeding ones may be set at an angle to pull the flue over as the exigencies of the situation may demand turns should be made as gradual as possible and slopes in the flue should be at an angle of not less than 45 degrees each flue must be absolutely independent inde pendent from fireplace to chimney top |