Having central air conditioning and heating is certainly a perk in many homeowners’ eyes, but like all major appliances in the house, your HVAC system should be well maintained to ensure its maximum efficiency. One of the most important — yet sometimes confusing — parts of an HVAC system is the air filter.

At its most basic function, an air filter removes impurities such as dust, pet dander or even bacteria from the air flowing through the system. Not only does this improve the air quality within your home, but it also protects your HVAC system from damage.

“Research indicates that people spend approximately 90 percent of their time indoors,” says HGTV star and Trane Residential partner Anthony Carrino, citing Environmental Protection Agency data. “Today’s homes are better insulated, more tightly sealed and more energy efficient; however, these factors can trap indoor pollutants, making indoor air up to five times less healthy than outdoor air.”

To help you master the ins and outs of air filters, we’ve put together a handy guide with everything you need to know.

What are the different types of air filters?

Air filters come in a number of shapes and materials, each with different capabilities and price points.

Flat-panel: Typically the most affordable type of air filter, traditional flat-panel models have fibers — most commonly fiberglass — stretched over a framework. They’re disposable and easy to install, but they aren’t necessarily the highest quality, allowing many particles to get through.

Pleated: Disposable pleated filters use dense screens of cotton or plastic fibers to remove particles from the air. Unlike their flat-panel cousins, they have pleats, which provide more surface area for filtration and allow the filter to catch more debris. The price point is slightly higher than that of flat-panel filters.

Electrostatic: Some air filters are electrostatically charged to trap more (and smaller) particles such as pollen, smoke or bacteria within their screens. They can be flat or pleated, and they can be disposable or washable.

Washable: Washable or reusable filters come in both ­flat-panel and pleated options, and they can be hosed down with water or vacuumed to remove any ­particle buildup. They are more eco-friendly than disposable filters, but there is somewhat of a catch, especially if you have an electrostatically charged filter. “Reusable filters will lose their electrostatic charge over time, which causes the filter to lose the ability to capture smaller particles,” says Scott Blackwell, merchandising vice president of rough plumbing and electrical at Lowe’s. So even washable filters have a life span — usually a handful of years.

High-efficiency particulate air (HEPA): The title of “HEPA” is assigned to any filter that consistently removes at least 99.97 percent of particles in the air that are 0.3 microns or larger. It’s a title endorsed by the Energy Department. Though they’re most commonly used in commercial settings that require ­extremely clean air, such as hospitals and laboratories, they can be used in households where people suffer from allergies or have a compromised immune system. Not all HVAC systems are ­designed to handle the super-dense HEPA filters, however.

What's the meaning of all those numbers?

All air filters are rated for their ability to remove particles from the air. The industry standard is the Minimum Efficiency Reporting Value (MERV), a scale from one to 16 developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers. It designates weaker filters with lower numbers and stronger ones with higher values. Some brands have created their own rating systems, such as Home Depot’s Filter Performance Rating and 3M’s Microparticle Performance Rating.

Another rating method is the Clean Air Delivery Rate (CADR), a scale recognized by the Federal Trade Commission and the Environmental Protection Agency that also measures air purifier efficiency. As with MERV, higher numbers equal better overall performance in terms of particle removal. Most filters fall between the 12 CADR and 240 CADR range, though some high-performance ones can go up to 1,200 CADR.

How do I choose the best air filter for my home?

Start by determining the specific needs of the occupants in your home, which should ­directly correlate with the CADR or MERV ratings of your air filters.

“Filters with a higher CADR rating are the best choice for families who suffer from allergies, have pets in the home, deal with excessive dust or want to capture airborne bacteria,” Carrino says. The same concept applies to MERV ratings: Using a more restrictive filter (one with a higher MERV rating) reduces the number of particles and allergens that end up in your home’s air.

But be careful of going too far with your filters. Some HVAC systems are not strong enough to push air through more restrictive filters that block the smallest particles — that is, ones with a higher MERV or CADR rating — which can reduce airflow and cause your home to be heated and cooled less efficiently. Overworking an HVAC system can also lead to hardware damage — and an expensive repair. Consult your HVAC system’s manual to determine how strong your model is, or call an HVAC technician.

Once you’ve narrowed down what rating range you’re looking for, you can factor in your budget. In general, disposable fiberglass filters are the most affordable upfront, starting at roughly $5, while washable filters start around $9, but they might save you more money over their lifetime.

Finally, you’ll need to take into consideration the dimensions of your ventilation openings and the spaces your HVAC system is servicing, which will determine what filter size and thickness you’ll need. (Keep in mind that thickness isn’t correlated with CADR or MERV ratings.)

How do I maintain an air filter?

Proper maintenance of air filters — either replacing or washing them regularly — is crucial not only to providing clean air in your home, but also to keeping your HVAC system functioning properly. “Maintaining your air filter is easy,” Carrino says. “Most filters are easy to slide or swap out, and it’s one of the few things you can do to maintain your filter without the help of a trained specialist.”

Although you should check the instructions for both your HVAC system and your specific filter for maintenance guidelines, you typically should change filters at least every season, if not once a month. “Even a high-quality filter can’t do its job right if it’s clogged with debris,” Blackwell says. “If you live in a brand new home or have remodeling or construction going on at your house, you’ll need to change your air filter more frequently to compensate for the extra dust and residue in the air.”

Blackwell suggests that you write the date you changed your filter on its spine so you can keep track of your maintenance schedule. Or, thanks to today’s smart-home technology, you can even buy smart filters such as 3M’s Filtrete Smart Air Filters that use sensors to monitor air flow. Such filters will send an alert to a mobile app to let you know when you need to change it.

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