The category 3 horizontal 6-in vent kit provides class 3 single wall ducting for use with Mr. Heater Big Maxx unit heaters, ranging from 250,000 to 400,000 BTUs. Complies with US standard (UL1738) and Canadian standard (S636). Designed for horizontal installation only. Kit includes a 6-in male connector, a 45-degree elbow, a 6-in to 19-in long adjustable 6-in diameter vent pipe, a 12-in long 6-in diameter vent pipe, a 24-in long 6-in diameter vent pipe, 6-in INS wall penetration, screened termination, screws, and silicone sealant. Stainless steel is required for horizontal installations per new category 3 certifications. Other parts may also be required for your specific installation needs. Please check and adhere to all state and local codes before installation.