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• Vertical Direct Venting System Installation
These installations utilize the boiler mounted blower to draw combustion air from outdoors and uses the natural buoyancy
of the heated flue products to create a thermal driving head that expels the exhaust gases from the flue. The negative draft
must be within the range of 0.01 to 0.08” negative W.C. to insure proper operation. The vent material must be in accor-
dance with the above instructions for vent materials. Vent material must be listed by a nationally recognized test agency.
The maximum and minimum venting length for Category I appliance shall be determined per the latest edition of the National
Fuel Gas Code (U.S.) and CAN/CGA-B149.1 and .2 Installation Code (Canada).
The diameter of vent flue pipe should be sized according to part 11 of the latest edition of the National Fuel Gas Code (U.S.)
and part 7 and Appendix B of CAN/CGA-B149.1 and .2 installation code (Canada). The minimum flue pipe diameter for
conventional negative draft venting using double-wall B type vent is 7” for ADB 500, 8" for the ADB 750, and 9" for the ADB
1000.
NOTICE: Vent Adapter may have to be used to connect B vent to the unit. (For ADB 500, a 6" diameter to 7"
diameter adapter is needed).
The connection from the appliance vent to the stack must be as direct as possible and should be the same as or larger than
the vent outlet. The vent must be installed to prevent accumulation of condensate and, where necessary, have means
provided for drainage of condensate. The horizontal breaching of a vent must have an upward slope of not less than 1/4
inch per linear foot from the boiler to the vent terminal. The horizontal portions of the vent shall also be supported for the
design and weight of the material employed to maintain clearances and to prevent physical damage or separation of joints.
• Vertical Direct Vent Termination
The vent terminal should be vertical and should terminate outside the building at least two (2) feet above the highest
point of the roof within 10 feet. The vent cap should have a minimum clearance of four (4) feet horizontally from and
in no case above or below (unless a four (4) foot horizontal distance is maintained) electric meters, gas meters,
regulators and relief equipment. The distance of the vent terminal from adjacent public walkways, adjacent buildings,
open windows and building openings must be consistent with the National Fuel Gas Code, or in Canada, the latest
edition of CAN/CGA-B149.1 and .2. Installation Code for Gas Burning Appliances and Equipment. Gas vents supported
only by flashing and extended above the roof more than five feet should be securely guyed or braced to withstand snow
and wind loads.
The vertical direct vent cap is designed for roof top mounting only. The air inlet opening MUST be installed one (1) foot
above the roof line or above normal snow levels that might obstruct combustion air flow. This dimension is critical to the
correct operation of the boiler and venting system and reduces the chance of blockage from snow. The vent cap must have
a minimum 3 foot vertical clearance above the air inlet opening.
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