There are three standard chimney installations for factory built chimneys. Some components are common to all three. Each type of installation should use flashing and a sealed storm collar at the roofline to prevent water from entering the house. Manufacturers require that chimneys extending beyond a certain height above the roof (frequently, 5 ft. or more) must also be braced. A chimney cap helps keep out rain, birds and other animals, and may reduce downdrafts. If a chimney cap includes a spark arrester, it should be inspected and cleaned regularly.

Beyond these common components, the three standard installations call for different parts and installation. This page will focus on the Standard Flat Ceiling installation. Click the names for information on Cathedral Ceiling and Through the Wall installations.

Standard Flat Ceiling installation

When the chimney connector extends to a standard flat ceiling as show in the above illustration, a support package and sometimes a chimney connector adapter are installed at the ceiling. The exact location of the ceiling support package is, of course, determined by the location of the appliance and connector, which must be situated to meet minimum clearances to combustibles.

Working from the attic or roof, sufficient sections of factory-built chimney (available in different lengths) are installed to go through the space above the ceiling, then through and above the roof to the correct height above the roofline. The chimney sections should be stacked and locked and securely as specified by the manufacturer. The illustration show the use of a chimney support package, attic radiation (or insulation) shield, roof radiation shield, roof flashing, sealed storm collar, roof bracing system, and chimney cap.

A minimum clearance of 2 inches is typically required between the outside surface of the factory-built chimney and any combustibles or insulation; the air space around the chimney must never be filled with insulation or any other material. (Maintaining this air space is one of the purposes of the attic radiation shield, also referred to as attic insulation shield.)

On a flat ceiling, the support package is designed so that the required opening automatically establishes clearances to the combustible adjacent ceiling joists, as well as determines the length of chimney extending below the ceiling. The roof is more complex and calls for careful calculation and installation. The clearance distance between the outside surface of a chimney and combustibles is measured horizontally, at right angles to it. (The rationale and importance of this point is clear remembering that radiant energy travels in a straight line and delivers maximum heat to a surface perpendicular, or at a right angle to it.) By definition a pitched roof will not be at right angles to a vertical pipe. The pitch of the roof must therefore be considered in determining or calculating the size of the hole that is cut.

Carefully read the specifications, as outside diameters of the piping vary, and minimum clearances other than 2 inches are sometimes required by the manufacturer. The manufacturer's specified clearances must be adhered to at all times.