My Library

Chimneys may be used to vent oil- and gas-burning equipment, provided the flue lining complies with oil and gas appliance installation codes. Alternatively, the equipment may be vented through special gas vents approved for this purpose. A flue that serves a fireplace or wood stove cannot also serve as a flue for a gas- or propane-fired furnace. A furnace and hot water tank or a fireplace and wood stove can be connected to the same flue but there are limitations that should be checked with the local building department. A flue should be as vertical as possible and cannot be sloped at an angle of more than 45° from the vertical.
There are two types of chimneys and flues commonly used in residential construction: masonry chimneys and factory-built flues.
Masonry Chimneys A masonry chimney consists of a liner and an outer wall (Figure 145). Masonry chimneys must be built on a concrete footing designed to support the load. The size of the chimney depends on the number, size and arrangement of flues. The outer wall of a masonry chimney must not be less than 75 mm (3 in.) and must consist of solid masonry units. The NBC provides minimum sizes for round and rectangular flues for fireplace chimneys.
145 Installation of flue linings
sealant around flue 75 mm (3 in.) minimum solid masonry between linings
75 mm (3 in.) minimum