We all want to breathe clean air, but it can be hard to know which air filter is the best for our needs. Consumer Reports tests air filters for homes with forced air heating and cooling systems, and they have found that the best models are those that filter dust, pollen, and smoke from the air without impeding airflow. The CADR (Clean Air Delivery Rate) is a measure of how much clean air is produced by an air cleaner at its highest speed setting. The higher the CADR, the faster and more efficient the air cleaner will be.
Room air purifiers with HEPA filters typically achieve the highest CADR. In Consumer Reports' tests, a CADR greater than 240 receives a rating of Excellent; 240 to 180, Very Good; 179 to 120, Good; 119 to 60, Fair; and anyone below 60 scores a Poor rating. Ionized air molecules can bind to airborne particles and give them a charge, encouraging them to bind and create larger particles that may be easier to filter or large enough to deposit in air. However, Consumer Reports found that this type of purifier left the air loaded with particles in each configuration.
Activated carbon filters don't fight particles, so many air purifiers have an activated carbon filter and a pleated filter to trap particles. Thicker oven filters, some up to 5 inches, often provide superior air cleanliness and a long service life. Consumer Reports tests dust, pollen and smoke removal at the lowest speed setting to determine how well a model cleans the air of fine clay dust and cigarette smoke. Air purifiers with pleated filters use fans to force air through a dense network of fine fibers that trap particles.
It's worth considering separate machines for different rooms since air purifiers work best when cleaning one room at a time. They are especially good at quickly filtering common airborne allergens such as pollen and mold spores, pet dander, dust mites and their droppings, soot from cars, and tobacco, marijuana, and wildfire smoke. It is much more important to measure the effect of a filter on the total particle load in the room.