The Metal-Fab Model M gas vent system is designed for use with approved gas appliances burning only gas. This document details installation instructions, safety precautions, and component specifications based on the provided documentation. The system utilizes a double-wall construction with an aluminum alloy inner flue and a galvanized steel or galvalume steel outer casing. Proper installation, adhering to local codes and the guidelines outlined herein, is crucial for safe and effective operation. The documentation emphasizes the importance of using Metal-Fab supplied components to maintain UL approval and ensure performance.
System Components and Materials
The Metal-Fab Model M gas vent system consists of sections and components that are interconnected using a slip fit and secured with sheet metal screws (#8 x ½ inch or 13mm). The vent is constructed from aluminum alloy for the inner flue, chosen for its rapid warm-up and improved draft capabilities, and galvanized steel or galvalume steel for the outer casing. The system is intended for use with gas appliances specifically designed to burn only gas. It is not approved for use with unlisted gas appliances, incinerators, recessed heaters, conversion burners, gas/oil burners, or appliances convertible to solid or liquid fuels.
Installation Procedures
Installation of the Model M gas vent system begins at the appliance outlet or the top of the drafthood. Each section or component is secured with the provided screws. When running the vent through insulated areas, headers must be installed to prevent insulation from contacting the vent itself. For installations penetrating floors, ceilings, or roofs, the surrounding materials must have a fire rating equal to or greater than those structural elements. Penetration of the flue with screws is limited to attaching the drafthood to the appliance outlet or the vent to a single-wall connector. A vent cap should be installed on all systems to prevent back drafts and to exclude rain and debris.
Clearance to Combustibles
Maintaining appropriate clearance to combustible materials is a critical safety consideration. For vent sizes 16-inch through 24-inch, a one-inch clearance to combustibles is required. For vent sizes 26-inch through 30-inch, a two-inch clearance to combustibles is required. These clearances apply to all other materials surrounding the vent.
Vent Support Requirements
For vertical vent heights exceeding 30 feet (9144mm), a vent support plate (MSP or MHS) is required at intervals along the vent’s length. The documentation does not specify the exact intervals between supports beyond this 30-foot threshold.
Considerations for Masonry Chimneys
When venting into an unlined masonry chimney, condensation may occur. To mitigate this, the documentation recommends installing the Type B vent inside the chimney. This provides an insulated barrier against temperature differences that contribute to condensation.
Limitations and Prohibited Uses
The Metal-Fab Type B gas vent system has specific limitations regarding its application. It is not to be used with appliances that can be converted to burn solid or liquid fuels. The use of draft increasers is restricted to the exhaust end of the vent system to maintain negative flue pressure. Vent sizing must be determined using tables found in NFPA54 (ANSI Z223.1, 2002) or by consulting with a Metal-Fab supplier. Installation must comply with both these guidelines and all applicable local code requirements. The vent is not intended for outdoor installation except when absolutely necessary, and in such cases, proper design must be verified using appropriate venting tables.
Safety Precautions
The documentation includes a caution regarding UL approval. UL approval is contingent upon using only Metal-Fab supplied components. Using non-approved parts may compromise performance and create a safety hazard. The vent must maintain the specified clearances to combustible materials. It is also cautioned that installing the vent outside should be avoided unless absolutely necessary, and proper design must be verified.
Temperature Considerations
The documentation notes the importance of maintaining a vent temperature that avoids excessive condensate production. This suggests that proper appliance operation and vent sizing are crucial for preventing moisture buildup within the vent system.
Component Assembly
The Model M gas vent sections and components are assembled by inserting one section into another and securing them with sheet metal screws. Figure 1 (not provided in the source data) illustrates this assembly process.
Additional Notes
The documentation states that in areas where solid or liquid fuels are common, the vent should be enclosed with materials having a fire rating equal to or greater than the floor, ceiling, or roof.
The provided source material is insufficient to produce a 2000-word article. Below is a factual summary based on available data.