What is the best furnace filter for indoor air quality?

Installing the best furnace filter will significantly improve your indoor air quality. (Photo by Brandon Smith)

Installing the best furnace filter will significantly improve your indoor air quality. (Photo by Brandon Smith)

Indoor air pollutants rate among the top five environmental health risks today, according to the Environmental Protection Agency. Air-tight construction and home insulation contribute to poor indoor air quality. Although these home improvements stop drafts and save on energy costs, they stop fresh air from coming into your home and pollutants from leaving.

Consequently, you have two options to improve indoor air quality: allow clean exterior air into the residence to provide ventilation or use an air cleaning device that removes indoor pollutants.

You can choose between two types of air cleaning devices for the removal of airborne pollutants: electronic air cleaners and mechanical air filters. Air filters consist of porous membranes that allow air to flow through while trapping dust, pollen, dust mites, pet dander and some mold spores.

To help measure the efficiency of filters installed in the duct work system of heating and cooling units, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has a rating system called the minimum efficiency reporting value (MERV). These ratings range from 1 (lowest) to 20 (highest), and shows three things:

  • the ability of the air filter to remove particles
  • the ability of the air filter to resist airflow
  • the product's expected operating life

To choose the best furnace filter, you should familiarize yourself with the four main types.

Flat-paneled fiberglass air filters

Usually carrying ratings of 1 to 4, flat-paneled fiberglass air filters consist of a disposable filter made of layered fiberglass fibers. A metal-like grating reinforces and supports the fiberglass material and helps prevent the filter from collapsing.

Inexpensive air filters mostly provide protection for heating and cooling components and not for cleaning the air. The filters have a medium efficiency rating for capturing larger airborne particles and a low efficiency for filtering dust mites, viruses, bacteria and dander.

furnace technician installs filter
A technician with highly rated B&W Heating and Air Conditioning in Indianapolis installs a MERV 11 air filter. (Photo by Brandon Smith)

Pleated polyester filters

Similar to fiberglass filters, disposable pleated polyester filters have a sizable surface field and a rating of 5 to 13. The medium efficiency rating makes them efficient at filtering small to large particles. Filters with a rating of 7 to 13 provide a level of effectiveness compatible with absolute high-efficiency particulate air (HEPA) filters, but at a lower price point.

These filters also have less airflow resistance compared to HEPA filters and support quieter operation of the blower fan. Pleated filters also come in higher efficiency models with a rating of 14 to 16. They have the physical appearance of true HEPA filters and are often confused with HEPA products.

HEPA filters

HEPA filters are recognized by the Occupational Safety and Health Administration and EPA as the ultimate product for cleansing airborne particles. HEPA products filter air at a very fine level, blocking elements that are 0.3 microns or larger. These filters catch 99.97 percent of all particles.

HEPA filters have an efficiency rating of 17 to 20. Most residential heating and cooling systems can't accommodate HEPA filters because of the product's dimensions and resistance to airflow. Switching to HEPA filters will significantly improve your indoor air quality but probably require calling a heating and cooling professional to retrofit your furnace.

Washable air filters

Permanent and washable filters are fabricated from plastic or metal frames. These products have a few layers of polypropylene weave or wire mesh material that stops certain pollutants. The durability of the filtration material makes it cleanable and reusable. Daniel Sinclair, owner of highly rated Sinclair Heating, Cooling & Plumbing in Lubbock, Texas, says washable air filters come with some major drawbacks:

  • They're usually rated only 1 to 4 on the MERV scale. "If your house is exposed to smaller particles like pet dander, cigar smoke or hair spray, a washable air filter may not be as effective as a higher-rated disposable filter," Sinclair writes on his website.
  • Maintenance is a pain. "Once you’ve washed them, you’re not supposed to simply dump the water out," he writes. "Because that water was exposed to bacteria and other particulates, it’s considered a wastewater hazard and should be disposed of appropriately — creating extra work for you."
  • They can get moldy. When you wash these filters, they'll take a long time to dry. If you re-install them while they're still damp, they may develop fungi that your HVAC system can blow througout your home.
  • They cost more than a disposable filter. According to Sinclair, this means you're paying more for a filter that requires a lot of maintenance.

If you need more advice or are interested in switching to HEPA filters, talk to a highly rated heating service provider on Angie's List.

Editor's note: This is an updated version of a story originally published on April 22, 2013.

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A dirty or otherwise restrictive air filter can overwork your system, making it less efficient. (Photo courtesy of Top Notch Heating, Cooling & Plumbing)
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