Natural Draft Vertical Venting System Installation
Natural draft venting uses the natural buoyancy of the heated flue products to create a thermal driving head that expels the exhaust gases from the flue. The neg- ative draft must be within the range of 0.01 in. to 0.08 in. WC negative to ensure proper operation. The vent material must be in accordance with the above instruc- tions 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 lat- est edition of the National Fuel Gas Code (U.S.) or B149 Installation Code (Canada).
The diameter of vent flue pipe should be sized accord- ing to Part 11 of the latest edition of the National Fuel Gas Code (U.S.) and part 7 and appendix B of the CSA B149 Installation Code (Canada). The flue pipe diameter for conventional negative draft venting using
NOTE: Vent Adapter will have to be used to connect B vent to the unit.
The connection from the appliance vent to the stack must be as direct as possible and shall be the same diameter 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.
Natural Draft Vertical Vent
Termination
The vent terminal should be vertical and should termi- nate outside the building at least two (2) feet above the highest point of the roof that is 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 main- tained) 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 the CSA B149 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 with- stand snow and wind loads.
CAUTION: Listed vent cap terminal must be used and sized adequately to evacuate the flue products from the boilers.
Natural Draft Vertical Venting with Common Venting System, Category I Appliance Only
(NOT to be Utilized with
Manifolds that connect more than one boiler to a com- mon chimney must be sized to handle the combined load. Consult available guides for proper sizing of the manifold and the chimney. At no time should the area of the vent be less than the area of the largest boiler exhaust outlet.
WARNING: Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under a positive pressure.
CAUTION: Vent connectors for natural draft venting systems must be type “B” vent or better.
Common venting systems may be too large when an existing unit is removed. At the time of removal of an existing appliance, the following steps must be fol- lowed with each appliance remaining connected to the common venting system placed in operation, while the other appliances remaining connected to the common venting system are not in operation.
a)Seal any unused opening in the common venting system.
b)Visually inspect the venting system for proper size and horizontal pitch and determine there is no blockage or restriction, leakage, corrosion or other unsafe condition.
c)Insofar as is practical, close all building doors and windows and all doors between the space in which the appliances remaining connected to the com- mon venting system are located and other spaces of the building. Turn on clothes dryers and any
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