Raypak 399B-2339B Venting Configurations, Natural Draft Vertical Venting Category

Venting Configurations

For heaters connected to gas vents or chimneys, vent installations shall be in accordance with the NFGC (U.S.), or B149 (Canada), or applicable provisions of local building codes.

Natural Draft Vertical Venting (Category I)

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 nega- tive draft must be within the range of -.01 to -.08 in. WC as measured 12 in. above the appliance flue out- let to ensure proper operation. Vent material must be listed by a nationally recognized test agency.

The maximum and minimum venting length for Cate- gory I appliances shall be determined per the NFGC (U.S.) or B149 (Canada).

The diameter of vent flue pipe should be sized accord- ing to the NFGC (U.S.) and B149 (Canada). The minimum flue pipe diameter for conventional negative draft venting using double-wall Type B vent is: 6 in. for Models 399B and 499B, 8 in. for Models 649B, 749B and 899B, 10 in. for Model 989B, 12 in. for Models 1259B and 1529B, 14 in. for Models 1799B, 1999B and 2069B, and 16 in. for 2339B.

NOTE: A vent adapter (field-supplied) must be used to connect Type 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 di- ameter as, or larger than, the vent outlet. The horizontal breaching of a vent must have an upward slope of not less than 1/4 inch per linear foot from the heater 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 clear- ances and to prevent physical damage or separation of joints.

Fig. 25: Natural Draft Vertical Venting

(Category I)

Termination

The vent terminal should be vertical and should termi- nate outside the building at least 2 ft above the highest point of the roof that is within 10 ft. The vent cap should have a minimum clearance of 4 ft horizontally from and in no case above or below (unless a 4 ft hori- zontal 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 open- ings must be consistent with the NFGC (U.S.) or B149 (Canada). Gas vents supported only by flashing and extended above the roof more than 5 ft should be se- curely guyed or braced to withstand snow and wind loads.

CAUTION: A listed vent cap terminal, adequately sized, must be used to evacuate the flue products from the heaters.

Common Venting System

Manifolds that connect more than one heater to a com- mon chimney must be sized to handle the combined

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