What Is The Best 20x25x1 Air Filter For A Home Air Conditioner That Has Everything

The research

Who this is for
What is a MERV rating?
How to choose a filter by its MERV rating
A perfectly good HVAC filter: Nordic Pure MERV 12
Two other filters that should do a fine job
How often should I replace my filters during wildfire fume events?
Footnotes

Who this is for

Almost HVAC systems apply a standard 1-inch-thick filter, then we focused exclusively on 1-inch medium-efficiency MERV filters. These are installed either in wall-mounted air-return vents (most mutual in the South), or at the air handler (more than mutual in the Mid-Atlantic and northern states, where the air handler is oft placed in the basement, about the furnace). A correctly sized 1-inch MERV filter simply rests behind a bracket at the render register; if you're not sure what size you need, cheque the narrow side of an existing filter for the dimensions (similar "16 x 25 ten 1").

If your HVAC organisation uses a thicker filter (usually in the 4- to 5-inch range, and ordinarily mounted at the air handler), it was likely designed specifically for medium-efficiency MERV filtration. Y'all don't need our communication; simply replace the existing filter with one that has the same specs.

What is a MERV rating?

MERV stands for Minimum Efficiency Reporting Value, and is a mensurate of how well a filter removes particulates from the air. In that manner it's akin to the more familiar HEPA rating used on air purifiers. And similar the examination for HEPA rating, MERV testing mensurate a filter'south efficiency—the percentage of particles information technology captures—in a unmarried laissez passer. Air is loaded with particulate thing, sent through the filter a single time, and the results measured. In real-globe utilise, with the air in your home constantly recirculating through the ducts and passing through the filters each time, the cumulative effect of the filters rises.

But MERV is dissimilar in some key means. First, instead of being a uncomplicated pass-neglect measure like HEPA (a filter is either HEPA-rated or it's not), MERV ratings autumn on a scale from i to sixteen, with college numbers indicating better functioning.

Too unlike HEPA, MERV tests measure particulates of different sizes, from 0.three micron (very small and hard to filter—the size HEPA tests measure) up to 10 microns (relatively big and like shooting fish in a barrel to filter). MERV too doesn't take a target pct for removal, the way HEPA does. Instead, the actual pct removal is recorded for each of 12 particle sizes, and these numbers are referenced against a performance table to make up one's mind the appropriate rating.

So when you expect at the total spectrum of what's floating around in the air in your house, MERV ratings reflect a filter's functioning on all of it. Higher numbers indicate a better filtration of the smaller particles, like pollen and smoke, that cause many respiratory bug. And medium-efficiency MERV filters in the 8 to xiii range—the kind nosotros would get—tin remove 90 percent or more of these. (For a really thorough explanation of how MERV ratings are calculated, visit the website of the National Air Filtration Association.)

One more matter: Some companies, including major filter manufacturer 3M/Filtrete and major filter retailer Abode Depot, use their ain rating conventions (MPR past Filtrete and FPR by Home Depot). Both claim to be based on the American Society of Heating, Refrigeration, and Ac Engineers'due south ASHRAE 52.2 standard that's used to set MERV ratings, but neither company provides an hands accessible explanation of how its own ratings differ from or compare with MERV. (Filtrete does print MPR and MERV equivalents on the frames of its filters, but you can't come across that until you lot've actually got one in your hands.)

Afterwards we inquired, Filtrete replied that its MPR filters capture more than of the very small-scale particles (0.3 to 1 micron) than equivalent MERV-rated filters when tested to ASHRAE 52.2 protocol, and shared a test summary that backs this up; on the larger particles (ane to 10 or more microns), MERV and MPR performance was nearly identical. Filtrete said MPR 1900 is equivalent to MERV thirteen, MPR 1500 to MERV 12, and MPR thou to MERV eleven.

Home Depot shared a basic comparative chart just no test information or protocols; it equates FPR 9 and 10 to MERV 12, FPR vii and 8 to MERV eleven, and FPR 6 to MERV 10.

How to choose a filter by its MERV rating

A stack of the filters we tested — Photograph: Michael Hession

To decide what filter nosotros'd buy, nosotros needed a more businesslike explanation of MERV, and so we turned to Kathleen Owen, a inquiry engineer specializing in air filtration. Owen almost literally wrote the book on MERV: In the 1990s she helped define the American Society of Heating, Refrigeration, and Air-Conditioning Engineers's ASHRAE 52.ii standard that's used to set the ratings. She later chaired the ASHRAE 52.2 commission, which regularly updates the standard to address changes in filter applied science.

In a chat about the almost common filter levels for sale at retail, MERV ane through 16, Owen said this range "gets you from filters that might catch a golf ball—I'k exaggerating a petty bit—upward to filters that will catch almost everything." Owen added, "I like to tell people that each of those filters has a purpose."

• MERV i to 4 (and unrated): Filters similar the MERV 4 E-Z Menstruation, MERV 2 True Bluish, MERV i Filtrete Bones Cut-To-Fit, and the unrated Flanders, are the cheapest (some under $i apiece) and almost basic MERV-rated filters. Their purpose is to go on particles larger than 10 microns—including pet hair (just not dander), rug fibers, and heavy dust—from bottleneck the heating/cooling coils and ducts in your HVAC organization. They take footling to no impact on fine particulates like pollen and fume, so they will not practice much to ease respiratory issues. But even with their limitations, these filters aren't pointless. They prolong the life of your equipment and help keep it running efficiently in the heating and cooling seasons. "Think of how important your screen door is in summertime when there's flies out," Owen said. If y'all are reading this guide, you probably care too much virtually air quality to consider one of these filters, simply if you're living (or vacationing) in a rental and don't want to invest much—peculiarly if the existing filter is problematically old or dirty—replacing it with a MERV i to iv filter would be a fine quick gear up.

• MERV 5 to 7: Owen said filters in this range (like this MERV 7 Nordic Pure) were created every bit an comeback on the basic MERV 1 to 4 filters and designed to also filter out midsize particles (3 to 10 microns, which includes most pollen and mold spores) that could encourage mold growth on heating/cooling coils. These filters are non as widely sold as the lower and higher MERV-rated filters in hardware stores, but they can be found online easily. At that place'south goose egg wrong with these types of filters; we just didn't focus on them as much as we did those in the eight to xiii range generally because this class, by comparison, usually isn't any cheaper, doesn't perform quite also, and often isn't as easy to detect.

• MERV eight to 13: This is the category we'd recommend for people who care about indoor air quality, and there are many equally good examples, such equally the Nordic Pure MERV x and MERV 12, the Honeywell FPR 9, and the Filtrete 1500. (For more particular on these models, see the A perfectly good HVAC filter and Two other filters that are too fine sections.) We focused on filters in the MERV 8 to xiii range because they are proficient to fantabulous at removing fine particulates (as small every bit 0.three to 3.0 microns in diameter, including smoke and exhaust particles and bacteria), plus annihilation larger. This MERV range, Owen said, "covers most of the stuff that people are probable to breathe in unless they're really shut to the source." The EPA says filters rated MERV 7 to 13 "are likely to be nearly equally constructive every bit truthful HEPA filters at controlling most airborne indoor particles." The higher cease of the range, MERV 11 to 13, removes twenty-plus to l-plus percent of the very smallest, 0.three-to-1.0-micron particulates, and filters in this range are especially popular. An NIH literature review indicates that filters in this range tin can significantly reduce indoor fine-particulate pollution and convalesce some respiratory ailments.

• MERV fourteen through sixteen: These are specialized filters that crave a purpose-built HVAC system; they're widely used in hospitals and some commercial and industrial environments, but mostly not in homes.

And then why doesn't everyone get a MERV eight to 13 filter? Across their higher toll, there is besides a concern your equipment might non be able to handle them, co-ordinate to engineers we interviewed from two of the major HVAC manufacturers: Jay Ayers of Trane and Doug Powell of Carrier. They (and Owen) all told usa MERV filters in this range restrict airflow more than than depression-MERV filters, as measured by the drop in air pressure the filters create when installed. That tin can potentially strain your equipment.

Powell noted that, "You accept a fair amount invested in your HVAC system, and unless y'all know how much pressure driblet you have in it and how much more it can handle, you could end up shortening the life of your blower. And a blower'due south not cheap." Ayers said, "That'southward the danger of looking at 1-inch filters and trying to go higher-efficiency and do the chore that's needed for allergies: You run the run a risk of really dissentious your blower and your HVAC arrangement." (If y'all are concerned virtually this, to be absolutely punctilious you can hire an HVAC firm to measure pressure drop in your system.¹)

Confronting these warnings, still, is a mountain of owner testimony that MERV 11, 12, and even 13 filters have worked just fine in their systems for years. Besides, an ofttimes-cited comprehensive contained test of MERV eight to thirteen filters' furnishings on HVAC airflow and energy consumption (a proxy for how difficult the equipment is working) concluded that even "if no accommodations are made for the greater pressure drop of high-MERV filters, air flow and energy penalties are not probable to be severe—at least, non until the filter is loaded with clay."

We feel the manufacturers' concerns are a scrap overcautious, in function because a contempo innovation in air filters permits high MERV ratings (eleven to thirteen) with low pressure drop.² And so-chosen electret filters use a mat of fibers that are electrostatically charged. The charge helps attract airborne particles (rather than but passively impeding them). Equally a result, the mat tin exist more than porous, causing better airflow and a smaller pressure level driblet. However, Owen emphasized, electrets become less efficient over time, often significantly and so. "Electret media will drop in efficiency upon use, sometimes by as much every bit 50 percent," she said. "Basically what happens is the tiny particles—we're talking forty, 50 nanometers, which there are gazillions of in the air—will coat the charged fibers and go along them from attracting larger particles." That ways regularly replacing electrets is absolutely key to maintaining practiced filtration, and almost come up with threescore- or xc-day replacement schedules. If you run your system twelvemonth-round, that's potentially six filters a year.

Given all this, we decided that if nosotros were buying new filters today, nosotros'd look for an electret filter effectually the MERV eight to 13 level with a low pressure drop that was both affordable and like shooting fish in a barrel to find.

A perfectly expert HVAC filter: Nordic Pure MERV 12

Nordic Pure's MERV 12 filter, a white corrugated fabric-looking material. — Photo: Michael Hession

Nordic Pure MERV 12

Nordic Pure's MERV 12 filters are not the only products that meet all our criteria, simply they are perfectly good examples, and they're usually competitively priced and easy to detect online. We similar that they're genuinely MERV-certified, considering unlike the proprietary ratings used by some bigger-proper name brands, the MERV criteria are publicly bachelor. Being rated MERV 12, the Nordic Pures will remove at least 35 percent of particles in the 0.three-to-1.0-micron range, which includes leaner and smoke; at least 80 percent of 1.0-to-3.0-micron particles, which include fine grit and soot; and at least 90 per centum of larger pollen, dust, pet hair, and lint particles. Once more, MERV stands for Minimum Efficiency Reporting Value, so this is the worst performance measured during third-party testing to the ASHRAE 52.2 standard. And again: the MERV test measures a single pass of polluted air through the filter. In your home, the air will continuously recirculate when your HVAC system is, leading to cumulatively greater filtration with each trip through the return registers.

Nordic Pure filters are mostly sold online, and the MERV 12s typically retail for a much lower cost than competitors—about $twoscore for a half-dozen-pack of 16-by-25-by-1-inch filters, or almost $vii each (with some competitors you'll pay nigh double that price for MERV xi/12 or the equivalent). At the recommended three-month replacement bike, a Nordic Pure can salve you well-nigh $thirty to $forty a year.

Nordic Pure reports the filter's force per unit area drop as 0.24 inch, which puts information technology a shade higher than the similar, MERV 12–equivalent Filtrete 1500 at 0.22 inch. But about people seem to have had no issues with the Nordic Pures straining their HVAC system—the half-dozen-pack has an overall score of 4.three stars (out of five) across more than than two,800 reviews at Amazon at this writing (we should note that the reviews once received an A rating from Fakespot; as of May 2019 that rating was downgraded to a C). The Nordic Pure MERV 12 filters are available in many sizes, then you should exist able to notice 1 that fits your return vent opening.

Two other filters that should do a fine job

A tester holding two 16 by 25 inch filters — Photograph: Michael Hession

If you can't discover Nordic Pure in your size, or if y'all adopt to purchase and pick up a new filter in a store immediately, Honeywell'south FPR nine filters and Filtrete'southward MPR 1500 filters are similar, and they're widely available at retail. (Home Depot stocks Honeywell; Lowe's and Ace stock Filtrete). These filters perform on a like level every bit the Nordic Pure MERV 12, they are well-reviewed by many owners, they come in a wide range of sizes, and the high likelihood that they're in stock at a nearby hardware store is a large advantage if you need one ASAP.

We don't beloved that neither Honeywell or Filtrete is MERV-certified, only their proprietary ratings are reportedly equivalent to MERV 11 or 12. We couldn't find pressure-drop information on the Honeywell, so that'south a possible business concern. The Filtrete'southward pressure driblet is 0.22 inch, fractionally lower than the Nordic Pure MERV 12's at 0.24 inch. Information Filtrete shared with us indicates the the 1500 removed 54 percentage of 0.3-to-1-micron particles in its ain tests, versus a minimum of 35 pct for the MERV 12-certified Nordic Pure. On larger particles, the two filters performed very similarly.

A major reason nosotros'd look for Nordic Pure as an selection get-go comes downward to price: Both the Honeywell and Filtrete options usually cost more than than twice the cost of the Nordic Pure filters. Every bit electret filters, all these models will lose effectiveness as they capture particles, and should be replaced at least every three months, per the manufacturers' recommendation. But homes with certain challenging conditions—if you smoke, frequently use candles or fireplaces, or have pets—will significantly reduce that lifespan.³

Owen also offered a unproblematic way to judge if it's time for a bandy: "If you can get to your filter hands, one unproblematic matter you tin can do is but go take a look. If you lot tin can't see the filter media anymore, it'south been in there too long. Change information technology!"

How oftentimes should I replace my filters during wildfire smoke events?

During a wildfire, you'll need to modify your filters more ofttimes than you would under normal air weather, and there are a few indicators that can help you know when information technology's fourth dimension to supplant one.

Nosotros asked Kathleen Owen, the filtration expert we spoke with for this guide, for her advice. She replied in an email: "If I lived well-nigh the wildfires and didn't find the toll prohibitive, I'd probably change a iii-month filter every calendar month during the season. Or possibly after each major consequence— say if a fire gets close enough to be a big deal (rather than simply yous know virtually information technology from the news)."

Owen likewise noted that wildfire smoke is a complex mixture, incorporating both physical smoke particles (which filters trap permanently) and water vapor and volatile organic compounds (gases), which are non trapped—and the latter of which create the smoky scent. "The moisture particles or ones with gases adsorbed on them can be collected, then give off the smelly stuff the adjacent time the fan comes on," she wrote. "Then, one recommendation is that if folks experience similar the air breathes easier or smells OK with the HVAC on but are gagging in the first infinitesimal or two the HVAC is on again, changing the filter could help."

There are likewise visual cues you can wait for when judging whether to supplant your furnace filter, Owen wrote. Bottleneck increases the pressure differential between the intake and outflow sides, and this can cause the filter's pleats to flatten out or the frame of the filter to buckle. Both are bear witness that the smoky air is finding a path around the clogged filter rather than through it, and that it's time to install a new one.

In addition to obvious steps like keeping windows and doors closed, Owen also advised shutting off bath fans and range hoods, both of which vent direct to the outside and, as a result, depict an equal volume of smoky outdoor air in through window frames and other leaky spots.

Owen added that she'd also consider adding a portable air purifier with a VOC filter. All our purifier picks have them, and though in our tests against an extreme load of ethanol vapors we plant most of them ineffective, anecdotally we tin say that they seem to perform well nether fairly heavy smoke conditions. Both in guide author Tim Heffernan's flat and in our New York exam space, after running our top picks for a few hours, in that location was little olfactory evidence that hundreds of matches had been burned nearby.

Finally, Owen noted that the American Club of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) has begun working on building-filtration guidelines specific to wildfire weather condition. We'll be post-obit up on this as information technology develops. For more on this topic, please run across our reporting on how to clean wildfire fume from your home.