Filter Out Allergens, Odors and Chemicals with Disposable Safe Home Duo Filter Safe Home TM Duo furnace filters for 18 x 18 x 1 inch slots combine two filters for furnace filter efficiency for dust, dirt and pollen allergens and odors and chemicals. MERV 8 air purifier furnace filter with internal steel frame first filters out allergens and then odors and chemicals. Self sealing edges means dirt cannot go around it. Always check with your HVAC technician before changing from your current furnace filter. This unit is a MERV 8. Made in USA . Always install with the air going through the white pre-filter first. Change every 3 months for maximum efficiency. Use for furnace filter slots, temporary needs, or custom sizes in air return grills. The Duo replaces any 1 inch thick home air filter in any location and can last up to 3 months. Safe Home Duo Filter captures up to 95 per cent of common household allergens. Eliminates odors from pets, paint, cooking, and more.Uses high density carbonand advanced compounds including FormaldaSorb TM , a patented potassium permanganate product plus the activated carbon in the second layer of the filter trap gasses that can cause health issues. 2 stage air filter one MERV 8 rated polyester white allergen filter plus the activated carbon filter pad. Made in USA. Limited Warranty Free of manufacturing and material defects . If product is found defective within 30 days of purchase, it will be replaced at no additional charge. Safe Home Duo One Inch Thick Filter Installation Determine direction of air flow through your furnace. Fold excess filter media around internal steel frame. Slide Duo Furnace Filter into the one inch slot so air goes first through the white pre-filter. Tuck in any excess so you can place cover, if any, over the end of the filter slot. Note excess material helps seal edges to force all air through the filter. Change the Duo air filter at least every 3 months. Some conditions that feature pets, construction work,