2 Layers of Furnace Air Filtration Keep House Cleaner with 20 x 24 x 1 Inch Filter This Safe Home TM Duo air purifier filter combination combines two filter medias. MERV 8 for dust, dirt and pollen allergens plus a second layer for odors and chemicals. MERV 8 air purifier furnace filter fits any standard 1 inch filter slot for a 20x24 filter. Note Check with your HVAC technician to verify that your system is able enough to handle the density of a MERV 8 filter before purchasing this or any other MERV 8 filter. Install this MERV 8 with Air Flow First Going through the White Media. Made in USA Safe Home Duo Filter Features Dimensions Fits 20 x 24 x 1 slot Captures up to 95% of common household allergens Eliminates odors from pets, paint, cooking, and more Uses high density carbon and advanced compounds 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. Highlyeffective and affordable. 2 stage air filter one MERV 8 rated polyester white allergen filter plus the activated carbon filter pad. Internal metal frame nothing goes around filter Made in USA. 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, painting or smoking may produce more pollutants and require more frequent changes. How does the Duo work? The polyester outer layers remove pollen, mold spores, and other common allergens. The inner layer features FormaldaSorb TM and activated carbon that traps a variety of odors an This item ships from a separate warehouse and may require extra time for delivery.