How to Vent Out a Chimneyless Boiler

Determine the routing for your boiler vents. There should be no more than three elbows in the vent-pipe route. The run from the outside vent outlet to the boiler should not exceed the boiler manufacturer’s specification or 100 feet, whichever is lesser. Vent piping should be of the type and diameter specified by the boiler manufacturer, typically 3-inch or 4-inch pipe.

Select the exact spots on the exterior wall to pass through the vent pipes. In general, the combustion air intake and exhaust vents should be on the same wall, away from prevailing winds, with the air intake at least 8 inches below and 8 inches to the side of the exhaust. The boiler’s exhaust vent must be at least 3 feet away from a house ventilation intake. The pipes must be at least 1 foot above average winter snow levels. Drill a starter hole in the wall to fit in the blade of the reciprocating saw. Cut a hole in the wall with the reciprocating saw large enough to pass the vent pipe through. The chosen place should be between studs and not have any pipes or wiring running through it.

Measure the horizontal distance from the center of the boiler vent openings to the outside of the wall. Add 12 inches to the horizontal measurement. This is how far the vent must protrude from the wall. Measure the vertical distance from the boiler vent openings to the centers of the holes in the wall. For the exhaust vent, subtract at least 1/4 inch from the vertical measurement for each foot of horizontal distance. This slope will allow condensed moisture from the exhaust vent pipe to drain back into the boiler.

Cut PVC or metal pipe sections to the lengths indicated by your horizontal and vertical measurements. For PVC, paint the connection points with PVC primer. Apply PVC cement according to manufacturer’s directions and fit the pipes and elbows together. For metal pipe, connect pipe pieces and elbows with the connector systems specified by the vent pipe manufacturer and fit the pieces together. Build the vent pipe in sections if necessary and assemble them at final installation.

Pass the horizontal intake and exhaust vent pipes through the wall. Fit the vertical pipes to the boiler’s vent outlets using the connection method specified by the boiler manufacturer. Install vent pipe hangers every 4 horizontal feet for long runs of vent pipe. Install exterior wall shielding and cap fittings specified by the vent pipe or boiler manufacturer.