Gas Engineering Guide

Venting – Vent Connectors

Connectors shall be used to connect fuel-burning appliances of a vertical chimney or vent unless the chimney or vent is attached directly to the appliance. (NFPA 54, 12.11.1). Such connectors shall be installed within the space or area in which the appliance is located and shall be connected to a chimney or vent in such a manner as to maintain the clearance to combustibles as required by the listing and the manufacturer’s installation instructions.

EXCEPTION: Listed appliances with integral venting systems such as direct vent appliances need not comply.

Every portion of a vent connector shall have a rise of not less than 1/4-inch per linear foot from the appliance to the vertical vent, or chimney. (NFPA 54, 12.11.7).

Exception: Vent connectors attached to a mechanical draft system installed in accordance with appliance and the draft system manufacturers’ instructions.

A connector shall be as short and straight as possible.

The horizontal run of an un-insulated connector to a natural draft chimney shall not be more than 75 percent of the height of the vertical portion of the chimney above the connector, unless part of an engineered system. (NFPA 54,

The horizontal run of an insulated connector to a natural draft chimney serving a single fuel-fired appliance shall not be more than 100 percent of the height of the vertical portion of the chimney above the connector, unless part of an engineered system. The horizontal length, design and construction of combined connectors, or connectors to a manifold joining two or more appliances to a chimney, shall be determined in accordance with approved engineering methods. (NFPA 54,

An appliance shall be located as close as practical to the venting system. Connectors shall not pass through an area or occupancy separation. (NFPA 54, A.12.11.8).

When the connector used for gas appliance must be located or pass through a crawl space or other cold area, that portion of the connector shall be listed Type “B” or Type “L” vent material or be provided with an equivalent means of insulation.

Connectors shall be installed so as to avoid sharp turns or other construction features that would create excessive resistance to the flow of flue gases. No device that will obstruct the free flow of flue gases shall be installed in a connector. This shall not be construed to prohibit the use of devices specifically listed or approved for installation in a connector, such as heat reclaimers, draft regulators, and safety controls.

Connectors shall be securely supported and joints fastened with sheet metal screws, rivets, or other approved means. (NFPA 54, 12.11.6). At the point of connection of the single-wall connector to the double-wall gas vent, three sheet metal screws or rivets may be used as an approved means.

NOTE: Screws shall not penetrate inner liner on “B” vents. “B” vents shall not be cut to accommodate vent connectors – use factory “B” vent fittings.

Manually operated dampers shall not be placed in connectors of gas-burning appliances. Fixed baffles on the appliance side of draft hoods and draft regulators shall not be classified as dampers. Automatically operated dampers shall be listed and installed in accordance with the terms of the listing and arranged to prevent the initiation or increase of firing unless the damper is opened to a safe position.

Connectors shall be adequately supported for the design and weight of the materials employed to maintain proper clearances, to prevent physical damage and to prevent separation of the joints. (NFPA 54, 12.11.9).

The entire length of vent connectors shall be accessible for inspection, cleaning, and replacement, unless listed materials are used and approval has been obtained from the building official. (NFPA 54, 12.11.11).

A connector entering a masonry chimney shall extend through the wall to the inner face of the liner, but not beyond, and shall be firmly cemented to masonry. A thimble may be used to facilitate removal of the connector for cleaning, in which case the thimble shall be permanently cemented in place with high temperature cement. The chimney connector shall enter the chimney not less than 6 inches from the bottom of the chimney. The chimney shall be provided with a clean out. If 6 inches are not available, installing a capped tee in the connector next to the chimney shall provide a clean out.

On Type “B” listed systems, an inspection tee is not required, provided that the listed vent cap is of the type that will not allow entrance of birds or debris.

Vent connectors serving gravity vent type appliances shall not be connected to a venting system served by a power exhauster unless the connection is made on the negative pressure side of the power exhauster.

When a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance.

The venting system on all gas appliances shall be examined to see that they are properly installed, and have adequate draft and the products of combustion are going up the vent connector and vent properly. A match test will be made at the appliance draft hood, when the appliance is equipped with a draft hood, to insure proper draft.

When the appliance is not equipped with a draft hood, the vent safeguard switches shall be checked for proper wiring.

Vent connectors made of Type “B” or Type “L” material may be enclosed following inspection.

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