Venting is dictated by where the mechanical room sits and the home's structure, not by a preference between options.
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Quick answer
A condensing Triangle Tube boiler vents through sealed PVC or polypropylene pipe, routed either horizontally through an exterior wall or vertically through the roof, pulling combustion air from outside rather than the mechanical room. Which option applies depends on the mechanical room's location relative to an exterior wall or roof access, and on meeting code-required clearances from windows, doors, and air intakes.
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Older, non-condensing boilers typically vented into a metal B-vent or a masonry chimney and drew combustion air from inside the mechanical room. A condensing boiler uses sealed combustion instead — a two-pipe system where one pipe draws outside air directly to the burner and the other exhausts flue gas outside, independent of room air. This removes any risk of a mechanical room depleting its own air supply and allows the vent to run through a wall or a smaller roof penetration rather than needing a full chimney.
An old masonry chimney that served a previous non-condensing boiler is typically oversized and poorly suited to a condensing unit's cooler, moister flue gas, which can lead to condensation problems inside the liner. Most condensing boiler installs abandon the old chimney for the boiler and vent through sealed pipe instead, leaving the chimney available for another appliance if one still uses it.
Sidewall venting routes intake and exhaust pipes horizontally through an exterior wall near the mechanical room, terminating a short distance outside. It's generally the simplest option when the mechanical room already backs onto an exterior wall, since it avoids running pipe up through multiple floors. Technical Safety BC's clearance requirements set minimum distances from windows, doors, soffit vents, and property lines, and in denser Metro Vancouver lots, particularly narrower infill and character home lots, those clearances often become the deciding factor in exactly where the termination lands.
Vertical venting sends the pipe up through the roof, which becomes necessary when the mechanical room is in a basement or interior location with no nearby exterior wall, or when sidewall clearance requirements can't be met. It generally means a longer pipe run, a roof penetration that needs proper flashing for Metro Vancouver's wet winters, and more labour than a sidewall vent, but it's sometimes the only workable path in an older character home with a centrally located mechanical room.
Roof terminations also need to clear nearby windows and maintain distance from adjacent structures, and in a home with a complex roofline, finding a penetration point that doesn't compromise water shedding takes planning before the install starts.
The choice follows from the mechanical room's location and the home's structure rather than personal preference. A technician walks the space, identifies the shortest code-compliant run to either an exterior wall or the roof, and factors in condensate drainage and winter freeze risk on any exposed exterior pipe run before finalizing the plan. In a cold snap, an improperly insulated or pitched condensate line can freeze and back up, which is one of the more common post-install issues in this climate when routing wasn't planned carefully the first time.
Safety note
Any work on the gas line, burner, venting, or combustion chamber of this unit must be done or verified by a licensed gas fitter. If you ever smell gas near the appliance, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location before doing anything else.
Sometimes, but code clearances from windows, doors, and intakes have to be met regardless of which option is shorter, so a technician checks both before recommending one.
Not directly — efficiency comes from the boiler's combustion design, not the vent path. Venting choice is about what's physically and code-achievable in your specific home.
It's typically capped or abandoned for the boiler and may still serve another appliance like a fireplace if applicable. A technician confirms it's properly sealed afterward.
It can if the condensate line runs through an unheated space or along an exterior wall without adequate pitch or insulation. Proper routing, and heat tape where needed, addresses this.
Generally yes, due to the longer pipe run and roof penetration work, though the exact difference depends on the specific home's layout.
Yes, venting changes on a gas appliance require a permit and inspection through the local municipality, and the work must be done by a licensed gas fitter.
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