The AllerAir® 4000 Series is the smallest, most compact series available for chemicals, gases, odors and particulate matter. It provides wide spectrum protection at an outstanding price. The 4000 Series is recommended for areas where space is a primary concern. It features a more compact design than the 5000 Series, while still offering reliable chemical, gas, odor and particle filtration. The AllerAir® 4000 Series utilizes a specialized carbon stage which contains between 12 lbs. and 18 lbs. of activated carbon in addition to a medical-grade HEPA filtration stage and an easy-clean pre-filter.