AC Infinity Air Filter Box with High Efficacy Filter, 4"A duct filter box designed for use with inline fans to circulate fresh air and block dust and odors. Built with 1mm thick cold rolled steel and aluminum duct flanges, able to withstand extreme weather. Slide lock door gives easy access to inner chamber while soft neoprene layer creates dust free seal. Includes a standard high efficacy filter that traps particles like dust, dirt, lint, and odor. A whole house air filtration system designed for use with