6. Neglect of the connection between smoke pipe and flue or of the flue
itself. The connection should be tight; rusted pipe should be replaced;
the chimney should be kept clean and the joints in the brickwork properly
pointed.
7. Lack of a tight flue. A flue free from leakage is unusual. Every
flue should be tight enough to prevent escape of smoke when tested as
described on page 14. A leaky flue is the most frequent cause of heating
troubles, high fuel bills, and destructive fires.
8. Failure to maintain the full sectional area at the bend when a flue is
offset.
9. Use of the main heating apparatus flue for water heater or other
auxiliary equipment. The furnace or heater should have a separate flue.
10. Failure to provide a separate tight cleanout for each flue. Two or
more otherwise good flues may be rendered inefficient if led into one
cleanout, since air may be drawn from one into another and the draft in
all affected.
11. Presence of deep pockets leading to cleanouts. They may cause eddying
currents that are detrimental. Pockets should be only deep enough to
permit installing a cast-iron cleanout frame and door just below the
smoke pipe entrance. Deep pockets allow soot accumulation that may take
fire.