Have you wondered how to choose the best furnace air filter for your home? Walking down the aisle at a home improvement store; or worse, scrolling through various air filter options online can make anyone's head spin given the number of options.
A few simple points can greatly simplify the selection process and make you feel more confident purchasing the right filter for your HVAC (heating, ventilation and air conditioning) system and family.
Mechanical vs. Electrical Home Air Filters
First, there are two basic types of air filters:
1) Mechanical. Mechanical air filters remove airborne pollutants by capturing them on the filter medium (think of a window screen or a laundry dryer filter).
2) Electrical. Electronic air filters use an electric field to attract and trap debris (think of a dirt magnet).
Most homes use mechanical filters because they are the cheapest. Your home likely has disposable, flat one-inch fiberglass filters that are very affordable, but do little to remove contaminants from the air. Some homeowners upgrade their flat or panel filter with pleated filters, which are more expensive, and provide more surface area to screen out allergy-causing particles.
Still other homeowners opt for filters in the electrical category, such as a self-contained unit that utilizes an electrical field to trap charged particles. People with severe allergies or who are very concerned about germs can consider a HEPA and/or ultraviolet filter.
With cost ranging from $1 up to $600, it’s sometimes hard to determine the best home air filter for you and your family. Whichever end of the spectrum you choose, it’s important to note that filter efficiency depends on a variety of factors including filter media (e.g., fiberglass, metal, manmade or natural fibers), as well as filter efficiency (e.g., fiber density/thickness or number of filter stages).
The easiest way to navigate these factors is by using the filter's MERV Rating.
Figuring Out Filter Effectiveness
Every HVAC air filter has a MERV rating, which measures how efficiently a filter captures pollutants that pass through your heating and cooling system. MERV ratings range from 1 (least efficient) to 16 (extremely efficient).
Some studies show that medium-efficiency filters — in the MERV 7 to 12 range — strike the best balance between allergen removal and filter cost.
But which is the best air filter for you? Common sense would suggest that you would choose an air filter with a higher MERV rating to ensure the best air quality. However, most residential heating and cooling systems cannot properly function with some of the denser filtration options that can limit airflow and strain the blower fan. In fact, most residential HVAC systems may require modifications for filters greater than MERV 8. Learn more about MERV ratings in this article.
Here’s a quick overview of common options to help you choose the best furnace air filter:
Flat, Disposal Filters
Standard spun fiberglass filters are designed to protect your HVAC system from large particles of dust.
At roughly $1-2 apiece, these basic filters might keep surfaces in your house a bit cleaner, but they can’t block the microscopic particles that are most irritating for allergy or asthma prone members of your household.
Most spun filters offer a MERV rating between 1-4.
Made from polyester or cotton paper, pleated filters are basically panel filters that have been pleated or folded to provide more surface area. The depth of these pleated or extended surface filters may vary from approximately 1 to 6 inches for medium-efficiency models and 6 to 12 inches for higher efficiency filters.
The average pleated filter offers three or four times the amount of surface area of a traditional flat filter. And, as a result, pleated filters can capture smaller, and a greater number, of particles without impeding the airflow of your furnace.
Standard pleated filters offer a MERV rating between 5-13.
Electronic Air cleaners
Electronic air cleaners use an electrical field to trap charged particles, thereby capturing a higher percentage of pollutants than Flat or Pleated filter media. The dirt and debris removed by the electronic air cleaner are microscopic—less than ten microns. (As a reference point, the eye of an average-size sewing needle is about 750 microns across, so we are talking about capturing particles that are 75 times smaller.) As these microns pass through the intense high voltage electric field, the particles are given an electric charge that draws them to a series of grounded plates that contain an opposite electrical charge. Pollutants are trapped here like a magnet until the collector cells or electrode panel are cleaned.
Importantly, as the collection plates/cells become coated with debris, the efficiency of the electronic air cleaner system is reduced. In fact, electronic air cleaners are the only air filtering device that becomes less efficient as it loads up.
Electronic air cleaners do not use a MERV rating.
High-efficiency particulate air (HEPA) filters are designed to block 99.97 percent of all particles 0.3 micron or larger. Most HEPA filters involve multi-stage sequences to capture smaller particles.
Because HEPA units work on the air exchange principle - air is cleaned by continually pulling air from the room into the filtering/cleaning device and exhausting clean air - their effectiveness is determined by calculating the number of air exchanges per hour in a given area. A home can have as many as 67 whole-house air changes a day depending on the house size and HVAC system. The greater the number of air changes in a home, the cleaner the air.
Available data indicate that even for very small particles, HEPA filters are not necessarily the preferred option, according to the U.S. Environmental Protection Agency. For these small particles, relatively large decreases in indoor concentrations (around 80 percent) are attainable with medium filter efficiency (such as a MERV rating of 13).
Typically, ultraviolet (UV) filters are a built-in component to an electronic air cleaner, or sold as add-ons to a whole-house electronic air filter. The ultraviolet light kills airborne bacteria and viruses, which is why hospitals use UV air filters.
The Decision: Which is the Best HVAC Air Filter for Your Home?
Most people will benefit by replacing a standard flat furnace air filter with a pleated filter. These cost less than $10 at many home improvement retailers.
The next step up is a medium-efficiency pleated filter that will remove most of the pollen, but still fits in the HVAC system's filter slot.
The electronic air cleaner is effective on a wide range of particle sizes and adds little pressure drop. With frequent cleaning it's around 90 percent efficient, but most electronic air cleaners, as well as HEPA filters, require modifications to your heating and cooling system.
HEPA filters are the most effective, but create significant pressure drop. Initial cost is around $500. Filters should last two to three years, but cost over $100 to replace.
Additional Resources About Air Cleaners and Home Furnace Air Filters
A more in-depth analysis of air cleaners is available in the EPA technical document "Residential Air Cleaners (Second Edition) A Summary of Available Information." Note the section about the available evidence of the usefulness of air filters.
You'll find valuable perspective in these owner manuals:
- Honeywell Electronic Air Cleaners - Owners Manual (pdf)
- Aprilaire Air Purifier - Owners Manual (pdf)
And about how valuable air filters are for your home:
- Tips About Your Furnace Filter from the American Lung Association from the Upper Midwest Health House (pdf)
- Air Filters Clear the Air
Which furnace air filter have you chosen for your home? Which factors were most critical to your decision? Let us know in the comments.