In 1987, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) designed a measurement scale known as MERV (Minimum Efficiency Reporting Value) to rate the effectiveness of air filters. The scale ranges with MERV ratings between 1 and 20, with 1 representing the least filtration and 20 the most effective filtration. The list below exhibits samples of MERV ratings, the likely use of filter rankings, and the particle size in micrometers that filters with corresponding MERV ratings are effective in capturing. MERV 20: Cleanroom (less than 0.3 um) MERV 16: General Surgery (0.3 – 1.0 um) MERV 12: Superior Residential (1.0 – 3.0 um) MERV 8: General Commercial (3.0 – 10.0 um) MERV 4: Minimal Filtration (greater than 10.0 um) The highest MERV ratings are rarely needed for “normal” homes and businesses. The smallest mold and Penicillium spores are trapped by filters with ratings between 8 and 16. Pollen, pet hair and dander, and insects are captured by filters with even lower ratings. Disposable, low-cost fiberglass filters are readily identified by their cardboard frames that expose the spun blue or green-colored glass. These filters have low MERV ratings of 1-to-4 and perform poorly at filtering even the largest particles. Medium-efficiency filters with MERV ratings of 5 to 13 perform better than their lower-cost counterparts by filtering small to large particles. Higher-efficiency filters with MERV ratings of 13-to-16 can capture even smaller particles at about 75 percent efficiency. Many filters advertise as HEPA or HEPA-like but fail when it comes down to removing airborne contaminants and pollutants from indoor air. True HEPA filters have MERV ratings between 17 and 20. True HEPA filtration provides the best indoor air quality by removing up to 99.97 percent of particles and bioaerosols. Using MERV as a guide to selecting the right air filter for your home or business is smart. The NATE-certified professionals at Pipe Works Services are ready to help you choose the filter that’s right for your home or business. Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information, click here to download our free Home Comfort Resource guide. Pipe Works Services serves Chatham, NJ, and the surrounding areas. To get started, check out our website.