In commercial boiler rooms the breeching is usually a large round or rectangular sheet metal duct, sometimes common to several boilers, with access doors, a draft control and test ports. Its size, rise and connections affect draft. Residential techs more often call the same thing the flue pipe or smoke pipe. Breeching joints that leak can pull in air and spoil draft or push flue gas into the room.
Drill a test port in the breeching 18 inches off the boiler outlet, before the barometric, and seal it after.
Also heard as
- flue connector
- smoke pipe
- flue pipe
- vent connector
Related terms
Draft
The pressure difference that pulls or pushes combustion gases through the boiler and out the chimney.
Flue gas
The hot exhaust that leaves the boiler after combustion, made up mostly of nitrogen, carbon dioxide, water vapor and leftover oxygen.
Barometric damper
A weighted swinging gate on the flue pipe that lets room air in to hold chimney draft steady.
Stack temperature
The temperature of the flue gas as it leaves the boiler, a direct measure of how much heat is going up the chimney.