Type B vent is a double-wall metal pipe designed for venting natural draft appliances like gas furnaces and water heaters that do not require forced ventilation. The double-wall construction provides insulation to prevent condensation and maintain draft efficiency. Type B pipe meets UL 441 standards and is the most common residential venting solution.
Construction and Materials
Type B vent consists of an inner aluminum or steel pipe surrounded by an outer steel jacket with an air space between them. The insulation layer reduces exterior surface temperature to approximately 140 to 160 degrees Fahrenheit, minimizing fire hazards. Common diameters range from 3 inches to 8 inches, with 4 inches being standard for most residential furnaces.
Installation Requirements
Type B vent must maintain proper rise and slope during installation, typically 1/4 inch of vertical rise per 12 inches of horizontal run. It requires clearance of at least 1 inch from combustible materials and cannot be used in attics or crawlspaces. Type B vent is cost-effective and relatively easy to install, making it the preferred choice for retrofit applications and new construction in residential settings.