Importance

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Abstract

Each longitudinal section of a concentric direct vent duct structure for a fuel-fired appliance, such as a furnace, is formed using a tubular outer duct having an axially spaced pair of triangular stand-off frame members anchored therein, and a smaller diameter inner duct having an axially spaced pair of ramped external annular locking projections thereon. To assemble the concentric duct section, the inner duct is simply axially inserted into the outer duct. As the inner duct is inserted into the outer duct, a ramped annular side surface on the leading inner duct locking projection resiliently and radially outwardly deflects side wall portions of the stand-off frame members and then permits them to snap back to their original undeflected positions. When the inner duct reaches its operative position within the outer duct, facing radially extending side surfaces on the locking projections straddle the stand-off frame members and act as abutments therewith to prevent removal of the inserted inner duct from the outer duct in either axial direction. The cooperation between the inner duct locking projections and the resiliently deflectable side wall portions of the stand-off frame members thus provides for a convenient snap-locking installation of the inner duct within the outer duct.

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First Claim