Flue Size
Flue size for the ordinary fireplace, enclosed on three sides, can be estimated by rule-of-thumb methods as an area proportionate to the size of the fireplace opening. However, cross drafts
and other problems encountered in
multi-opening fireplaces must be overcome by a stronger draft, and therefore larger flues are required. Since the fireplace opening size can vary not only vertically and horizontally, as in a single opening, but also by the number of sides open (two, three, four, or a complete circle), the flue must vary in proportion. Suggested flue sizes for different styles of fireplaces are listed elsewhere in these instructions.
General
Inspect the damper, making sure the valve plate is undamaged and free to operate, Check to see that the pull chains are securely fastened to the valve, with the "C" pull hanging from the side that opens above the damper body and the "O" from the valve side that opens down into the dome. Test the tension adjusting bolt I see diagram I and readjust if necessary for proper operation. Tighten the nut against the tension arm to hold the tension bolt in the set position.
Installation
Lay up the fireplace according to your plans until the desired opening height is reached i see specifications). The damper is now set in place, taking advantage of any built-up masonry sides as supporting ledges for the damper flanges. Any projecting corner should be supported by a suitable post of adequate strength. With the damper perfectly level, accurately measure and cut the post to the length needed and set in place. Now pad the corners of the damper body with the ½” glass wool provided, and continue laying up the masonry. Keep bricks and mortar at least ½” away from the damper to allow for expansion and contraction of the metal.
Smoke Shelf
The flue tile should never be set directly above the damper opening, but should be offset to one side. A smoke shelf, horizontal with the top of the damper, should be provided to impede and deflect downdrafts. It should be located directly beneath the flue tile, on any of the four sides of the damper. Actually, eight positions for the shelf and the chimney above it) are available, since the damper can be reversed. The smoke chamber above the damper and the shelf should be generous in size, high enough not to impede the movement of the damper valve, and should be corbelled steeply to meet the bottom of the flue lining. For a smooth surface and better draft, the walls should be given a coat of cement mortar. From this point on, the mason should follow the best recommended practices for good chimney construction.
