20 x 20 x 1 in (Actual Size: 19-5/8 x 19-5/8 x 3/4 in). Preferred. 37 times more effective than fiberglass filters. Pleated, electronically charged media is designed to provide peak performance up to 3 full months, removing airborne particles such as micro-allergens; dust mite debris; animal dander; plant spores; lint; dust; smoke; pollen. For furnace or central air. Pleated design provides maximum dirt-grabbing filter area with minimum resistance to airflow. The Ace Microparticle Air Filter provides more filter surface area by pleating the filter medium. And the more surface area you have, the greater the filter's ability to trap dirt, pollen and other particles while keeping airflow resistance low. Merv 11 Efficiency: The Ace Microparticle filter is rated as a Merv 11 according to ASHRAE test standard 52.2. Merv (Minimum Efficiency Reporting Value) is the minimum efficiency observed during testing of the filter. Filters typically are rated in the range of Merv 1-12. Higher ratings indicate more efficient filters. Compatible with your heating and air conditioning system. Ace air filters for furnace and central air are designed to fit and perform with most systems. Simply find the size that's right for you. Unlike washable filters, Ace Microparticle Air Filters are convenient to use and easy to replace. They are totally disposable. Under normal conditions, this filter will provide up to three months of thorough cleaning of your air. Electrostatic charge traps & holds tiny airborne particles. 99% of the particles in the air you breathe are smaller than 1 micron in size. By comparison, a human hair is 40 microns in diameter. Other filters allow these submicron sized particles to pass right through. But the Ace Microparticle filter's manufacturing process electrostatically charges the filter medium, creating an attraction that pulls these tiny particles from the air and holds them tightly to the filter. Ace Microparticle provides the best performance on the smallest airborne particles including bacteria, smoke and other allergens. UL listed - air filter units classified by Underwriters Laboratories, Inc. as to flammability only class II.