Height of Chimney Flues For Masonry and Concrete

(1)  A chimney flue shall extend not less than,

    (a)   900 mm above the highest point at which the chimney comes in contact with the roof, and

    (b)   600 mm above the highest roof surface or structure within 3 m of the chimney.


Article Ontario Regulation 332/12 Building Code,   Information published by oncodes.ca for educational purposes only.

Figure 144

Chimney height above the ridge


A chimney is a structure containing a flue or flues, which route any smoke and gases produced by a fire or furnace to the outside. A flue is a sealed pipe or channel that may be contained within a chimney or a self-contained unit independent of the chimney.

Chimneys and flues must be capable of producing sufficient draft to maintain the fire and remove the products of combustion. Chimneys, flues and fireplaces must be carefully built to minimize fire hazards. Ideally, they should not be located on outside walls. Locating them within the house keeps the chimney, flue and fireplace warmer, giving a better draft and reducing condensation inside them.

Chimneys and flues must extend at least 900 mm (36 in.) above the highest point where the roof meets a chimney and must be at least 600 mm (24 in.) higher than any roof surface within 3 m (10 ft.) of the chimney (Figure 144). 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.

Source : Canada Mortgage and Housing Corporation (CMHC)