How to vent combustion gases from a gas appliance?

Combustion gas venting (flue gas) is essential for safety and must comply with CSA B149.1:

Venting methods:

• Type B (standard chimney): Single-wall metal duct that exhausts hot gases outside. For natural draft appliances (atmospheric water heater, standard furnace). Terminates at least 300 mm above the roof
• Type C (concentric/coaxial): Double wall — fresh air enters through the outer ring, combustion gases exit through the center. For high-efficiency (condensing) appliances. More efficient, can terminate on an exterior wall (horizontal)
• Direct vent: Sealed system that takes air from outside and exhausts directly outside. Very safe for bedrooms

Important rules:

• Minimum distance from a window, door, or air intake: 1 meter for concentric venting
• Distance from ground: 300 mm minimum for wall termination
• Prohibited from terminating under a balcony, porch, or overhang
• The vent must be inspected annually and cleaned if obstructed

A carbon monoxide (CO) detector is mandatory in any room containing a gas appliance.