Chimney Design Solutions, Inc. represents the leading manufacturers of chimneys and gas vents. For your specific project, please contact our design team to discuss.
Each product has its specific application. When specifying chimneys or gas vents always require that the submittal confirms that the shop drawings’ proposed exhaust system complies with the appliance manufacturers’ listing and written instructions and that the chimney or vent system will safely exhaust the connected appliances.
For Listed Category I appliances, Listed appliances equipped with a draft hood, or Appliances listed for use with Type B gas vent, the gas vent system design shall be based upon the requirements set forth in the latest edition of ANSI Z223.1/NFPA 54, National Fuel Gas Code, including NFPA 54’s ‘Sizing of Category I Venting Systems’ and NFPA 54’s Vent Tables.
For all other Categories and types of appliances, the chimney or gas vent system design shall be based upon data provided by the appliance manufacturers’ written instructions. The draft calculation shall be based upon ASHRAE’s Steady-State Chimney Design Equations and submitted with the appliance manufacturers’ requirements for review and approval by the engineer.
UL 441 Type B Vent
UL 441 Type B Vent can only be specified for three types of appliances:
– Listed Category I appliances
– Listed appliances equipped with a draft hood
– Appliances listed for use with Type B gas vent
Gas vent systems are designed in accordance with NFPA 54. The typical gas vent has an aluminum inner wall and a galvanized or galvalume outer jacket. The air space between the walls varies from ¼” to 1″ depending upon the diameter of the gas vent.
UL 1738 Special Gas Vent
UL 1738 Special Gas Vent is specified for gas vent systems serving Category II, III, or IV appliances. Category II, III and IV vent systems are designed in accordance with the appliance manufacturer’s listing and written instructions. Special gas vents are available in single- or double-wall construction. Double-wall special gas vents are fabricated with a ferritic stainless steel inner wall, stainless steel outer jacket and a 1″ air space in between the walls. Most special gas vents require silicone sealant or gaskets at each joint; however, modern special gas vents use Viton or graphite to seal the joints. Viton and graphite do not deteriorate as rapidly as silicone in the presence of acid condensate.
Special gas vents are not intended for other condensing applications such as exhausting turbines or cogeneration systems.
UL 2561 1400°F Chimney
UL 2561 1400°F Chimney is typically specified for chimneys serving non-condensing commercial and industrial boilers where temperatures do not exceed 1400°F continuous and pressures do not exceed 60″W.C. These chimney systems are designed in accordance with the ASHRAE Steady-State Chimney Design Equations and the appliance manufacturer’s written instructions. The chimney is available with a 304 (for natural gas) or 316 (for fuel oil) stainless steel inner wall and an aluminized steel or stainless steel outer jacket. Various insulations are available which range from a 1″ air space to 4″ inches of fiber insulation, but most applications are specified with 1″ of fiber insulation.