Most notable is the 3M Filtrete line of furnace filters that uses the MPR rating system, then you have Home Depot that uses the FPR rating system and so on. So everyone is a little different and we are left to clear the air. We will give everyone credit as they are all attempts to simplify the buying process but only within that store or specific brand. The main thing to remember is the larger the number whether it be an MPR 2200, MERV 8 or an FPR of 4 the larger the number the better that filter will do at improving your indoor air quality within that specific furnace filter manufacturers filters or if the store you are shopping at uses a special rating scale...but then again shouldn't you just get your filters at www.rememberthefilter.com!
For more info on ratings and a buyers guide on purchasing furnace filters visit our FAQ section for more info.