Tucked away in your basement or attic, the air filter in your HVAC system is something you probably don’t think about much. But a good air filter will keep your oven and central air conditioning system running by protecting the mechanics from dust and dirt. And the best filters trap indoor pollutants like dust, pet hair and pollen, helping to purify the air in your home.

This is important because, according to the Environmental Protection Agency, the concentration of air pollutants in your home can be two to five times higher than what is normally found outdoors.

Below are the top air filters from the CR tests (grouped by thickness and listed in alphabetical order). We measure how well an air filter removes dust, pollen and smoke from the air and see how unhindered the air flows through the filter at every fan speed. We also calculate the annual cost of replacement filters based on the manufacturer’s recommendations for when to change them (remember, prices may vary by retailer; buying filters in bulk may also be cheaper).

“Different filters do better in our tests, and we’ve found that they don’t need to be replaced as often,” says Dave Trezza, who oversees CR’s air filter tests. But not every HVAC system can accommodate a thicker filter – the most common size is 1 inch thick – although you can upgrade some systems’ ducts to accommodate thicker filters.

Another thing to consider when shopping is the filter level specified by the manufacturer. The most commonly used system assigns each filter a MERV (Minimum Efficiency Report Value) number developed by ASHRAE (formerly the American Society of Heating, Refrigerating and Air-Conditioning Engineers). However, 3M and Home Depot have each developed their own classification systems called MPR (microparticle performance rating) and FPR (filter performance rating), respectively. “Regardless of the classification system, the higher the number, the better the filter can remove air pollutants,” says Trezza.

For more information on air filters, including some models to avoid, see our full air filter reviews and air filter buying guide.