Furnace filter buying guide - Everything you need to know to buy the best filter for your furnace

Your home's furnace is a multitasking powerhouse. In addition to keeping your home warm and comfortable on cold days, it can clean your air as well. Keep allergies under control and breath easy by installing a purifying air filter in your furnace. When shopping for a furnace filter, there are a number of factors to take into consideration. Your first step is to decide what you want your filter to do for you. Do you want it to just do the basics, trapping just dirt and lint? Or do you have allergies and want a filter that removes allergens from your home's air? Learning about the different filter rating systems will help you choose the best filter. From there, choose the filter type and size that will fit your furnace, and you'll be able to breathe easy, knowing you've purchased the best furnace filter.


MERV, MPR, FPR, HEPA, what do these terms mean? When the filters on the shelves are labeled with so many different ratings, it's hard to know what filter to choose. But while brands brands have created their own rating systems, at the end of the day, they are all rating the same filter and using similar measurement methods. Each system takes into consideration the percent of particles trapped and the size of the particles.


Filter Performance Rating is a rating system developed by The Home Depot for brands sold through their stores to indicate whether a filter's performance is considered good, better, best or premium.


High Efficiency Particulate Air filters must remove 99.97% of particles as small as 0.3 microns to meet filter guidelines set by the US Department of Energy. The HEPA rating only applies to air purifiers; it's not used for furnace or air conditioner filters.


The minimum efficiency reporting value or MERV is a rating system developed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers out of a need to evaluate the effectiveness of air filters. Using a scale of one to 20, MERV measures a filter's ability to capture unwanted airborne particles, as well as the size of the particles. The greater the percent of unwanted particles captured, and the smaller their size, the higher the rating. For example, a MERV 3-rated filter can remove only a small percent of the largest airborne particles, while a MERV 15 filter can trap some of the tiniest airborne particles.


Micro-Particle Performance Rating is a metric developed by 3M Filtrete indicating how effectively a filter can capture particles between 0.3 and 1 micron in size. MPR is a metric indicating good, better and best, with filters containing the highest MPR (1900 or greater) being the most effective at filtering airborne particles.


Disposable Fiberglass

The most basic of all filters, industry insiders call these Bugs and birds air filters. Made of thick-spun fiberglass with a coarse composition and wide spacing, they prevent large particles like dust, link and debris from entering the furnace but they do not clean or purify your air. Because they do not have the ability to trap things like pollen or dander, they are nor recommended if you have allergies or asthma. These inexpensive filters are commonly used in apartments.

Pleated filter

The most common distinction of a pleated air filter is also the most obvious. A pleated air filter, unlike its flat fiberglass style, doubles the amount of fabric to provide more surface area to capture airborne pollutants. As a result, it will have a naturally higher MERV rating, helping to reduce more pollutants from making it into your air. A cost-effective, high-efficiency filter, pleated filters can trap some small particles making them a good option if you have allergies. An added benefit of the extra surface area: less frequent replacement, saving you time and money.

Disposable electrostatic

Electrostatically charged fibers attract airborne particles like dust and lint, as well as smaller particles like smoke, resulting in cleaner air in your home. These filters are typically affordable in price, and are recommended for homes with kids, pets or smokers.

Permanent electrostatic

A relative of the disposable electrostatic, this permanent type contains self-charging cotton fibers that attract particles. The removable, machine-washable filter can be removed, washed and reused for up to 8 years.

High-efficiency pleated

The king of furnace filters. Made from pleated synthetic cotton that's attached to a very rigid metal grid to prevent leaks. This type of filter is commonly used in hospitals because of its ability to trap even the smallest of particles. Due to its extreme filtering ability, high-efficiency pleated filters can be expensive and require a special housing in order to handle its thick size.


The model number and size of your air filter will likely be printed on the filter itself. If not, some quick measurements will tell you what size replacement to buy. In addition to length and width, filters come with different thicknesses, typically ranging from one to four inches. A thicker air filter will help to trap more particles, but it may not fit your furnace or air conditioner. And in some cases, a thicker air filter may also impede airflow. Check the thickness of your current filter or look at the user manual to find out what the system can support. If your furnace will only accommodate a one-inch sized filter, you can maximize its effectiveness by checking it at least every 30 days and replacing it when it's getting dirty.


Determining what brand to use in your heating and cooling system is ultimately about function and performance not brand name. The difference between air filter brands is skin deep. Frequently made from the same types of raw material and designed to perform the same task, look beyond the brand. Choose the air filter that's best for your needs by considering the filter's rating, reading the product specs and knowing the particles you want removed from your air.


The lifespan of a filter depends on the type of media its made of, your air quality and the contaminants within your home, and where you live. While the general rule of thumb is to replace filters every 3 months, the best thing to do is check your air filter at least once per month. If it's getting dirty and clogged, replace it with a new one.
Pro tip: Whenever you buy a replacement filter, get at least two. That way you'll always have a clean filter on hand.


As the filter reaches the end of its life, the clogging makes the fan work harder and harder to push the air through the filter. This restriction can reduce the airflow through the house, and may affect the performance of the heating and cooling system. Resist the temptation to just wash your filter. While washing and reusing is often an eco-friendly and cost-saving option, it's not a safe or effective alternative to filter replacement. The unique filter fibers are not meant to get wet, and can be damaged or destroyed when washed. Additionally, exposure to water can significantly increase the presence of mold and bacteria in the filter, which would then be released into the air. Vacuuming isn't recommended because the delicate filter fibers can be easily torn or ripped. Because a vacuum isn't powerful enough to remove all the impurities trapped in a filter, it won't truly be clean and may release the unwanted particles into the heating or cooling system.