M3
CONDENSING WATER BOILER
22
34-1115 12/15
8.2.2 Vertical or Horizontal Vent Termination:
1. The vent terminal must have a minimum clearance of 4 feet (1.22 m) horizontally from, and in no case be
located above or below, unless a 4 foot (1.22 m) horizontal distance is maintained from electric meters, gas
meters, regulators and relief equipment.
2. The vent cap must terminate at least 3 feet (0.91 m) above any forced air inlet within 10 feet (3.05 m).
3. The vent shall terminate at least 4 feet (1.22 m) below, 4 feet (1.22 m) horizontally from or 1 foot (0.3 m) above
any door, window or building air inlet to the building.
4. The vent system shall terminate at least 1 foot (0.3 m) above grade and at least 1 foot (0.3m) above possible
snow accumulation levels and shall terminate at least 7 feet (2.13 m) above grade when located adjacent to
public walkways or gathering areas.
5. To avoid a blocked flue condition, keep the vent cap clear of snow, ice, leaves, debris, etc.
6. The vent must not exit over a public walkway, near soffit vents or crawl space vents or other areas where
condensate or vapor could create a nuisance or hazard or cause property or could be detrimental to the
operation of regulators, relief valves or other equipment.
7. A horizontal vent must extend one foot beyond the wall.
8. A horizontal vent terminal must not be installed closer than 3 feet (0.91m) from an inside corner of an L-shaped
structure.
9. A vertical vent must exhaust outside the building at least 3 feet (0.91m) above the point of the exit and at least 2
feet (0.61 m) above the highest point of the roof within a 10-foot (3.05 m) radius of the termination.
10. A vertical termination less than 10 feet (0.91 m) from a parapet wall must be a minimum of 2 feet (0.61 m)
higher than the parapet wall.
8.2.3 Combining Category IV Vents
Combined M3 Category IV gas vent systems must incorporate an Exhausto, Tjernlund or US Draft variable speed,
modulating, mechanical draft inducer capable of maintaining the appropriate negative draft at the end of the common
flue, to assure that all boilers in the combined vent system operate with a negative draft. Do not exceed negative
0.25” W.C. See the “Combining Vents with a Draft Inducer” illustration below.
Combining the exhaust vents of multiple M3 condensing boilers into a common, unpowered or “gravity” vent is never
recommended (i.e. venting as Category II). M3 boilers are too efficient and their flue products are too cold to
generate the natural buoyancy required for such combined vent systems to function reliably and safely.
WARNING: Do not connect multiple boilers vents into a single unpowered or fixed speed powered vent. This
could cause unsafe operation and the potential for poisonous carbon monoxide to enter occupied areas.
Such improper installation can cause property damage, personal injury, exposure to hazardous materials or
death.
Conventional Venting Through the Wall Venting Combining Vents with a Draft Inducer
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