What Are The Best Furnace Filters

The research

Who this is for
What is a MERV rating?
How to cull a filter past its MERV rating
A perfectly skilful HVAC filter: Nordic Pure MERV 12
Two other filters that should do a fine job
How ofttimes should I replace my filters during wildfire smoke events?
Footnotes

Who this is for

Almost HVAC systems apply a standard 1-inch-thick filter, so we focused exclusively on 1-inch medium-efficiency MERV filters. These are installed either in wall-mounted air-return vents (nigh common in the S), or at the air handler (more than common in the Mid-Atlantic and northern states, where the air handler is often placed in the basement, almost the furnace). A correctly sized one-inch MERV filter simply rests behind a bracket at the render annals; if you're not sure what size you need, check the narrow side of an existing filter for the dimensions (like "16 x 25 x 1").

If your HVAC system uses a thicker filter (usually in the four- to 5-inch range, and usually mounted at the air handler), information technology was likely designed specifically for medium-efficiency MERV filtration. You lot don't need our communication; but supersede the existing filter with one that has the aforementioned specs.

What is a MERV rating?

MERV stands for Minimum Efficiency Reporting Value, and is a measure of how well a filter removes particulates from the air. In that way it'southward akin to the more familiar HEPA rating used on air purifiers. And like the test for HEPA rating, MERV testing measure a filter's efficiency—the pct of particles it captures—in a single pass. Air is loaded with particulate thing, sent through the filter a unmarried time, and the results measured. In real-world use, with the air in your abode constantly recirculating through the ducts and passing through the filters each time, the cumulative effect of the filters rises.

Merely MERV is different in some key means. Commencement, instead of being a simple pass-fail measure like HEPA (a filter is either HEPA-rated or it's non), MERV ratings fall on a scale from 1 to 16, with higher numbers indicating better performance.

Also unlike HEPA, MERV tests measure particulates of different sizes, from 0.3 micron (very small and difficult to filter—the size HEPA tests measure out) up to 10 microns (relatively large and easy to filter). MERV besides doesn't take a target percentage for removal, the mode HEPA does. Instead, the actual percent removal is recorded for each of 12 particle sizes, and these numbers are referenced confronting a performance tabular array to determine the appropriate rating.

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

Ane more affair: Some companies, including major filter manufacturer 3M/Filtrete and major filter retailer Abode Depot, use their own rating conventions (MPR by Filtrete and FPR by Abode Depot). Both claim to exist based on the American Society of Heating, Refrigeration, and Air-conditioning Engineers's ASHRAE 52.2 standard that's used to fix MERV ratings, but neither visitor provides an hands accessible explanation of how its ain ratings differ from or compare with MERV. (Filtrete does print MPR and MERV equivalents on the frames of its filters, but you can't see that until you've really got one in your hands.)

Later nosotros inquired, Filtrete replied that its MPR filters capture more of the very small particles (0.3 to one 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 (1 to 10 or more than microns), MERV and MPR functioning was most identical. Filtrete said MPR 1900 is equivalent to MERV 13, MPR 1500 to MERV 12, and MPR 1000 to MERV eleven.

Dwelling Depot shared a bones comparative chart but no exam data or protocols; it equates FPR 9 and 10 to MERV 12, FPR 7 and eight to MERV 11, 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 make up one's mind what filter we'd buy, we needed a more pragmatic explanation of MERV, then we turned to Kathleen Owen, a enquiry 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'southward ASHRAE 52.2 standard that's used to set up the ratings. She later chaired the ASHRAE 52.two committee, which regularly updates the standard to address changes in filter applied science.

In a conversation nigh the most common filter levels for sale at retail, MERV 1 through sixteen, Owen said this range "gets you from filters that might catch a golf game ball—I'm exaggerating a little bit—up to filters that volition catch almost everything." Owen added, "I like to tell people that each of those filters has a purpose."

• MERV 1 to 4 (and unrated): Filters like the MERV 4 E-Z Flow, MERV 2 Truthful Blue, MERV 1 Filtrete Basic Cut-To-Fit, and the unrated Flanders, are the cheapest (some under $1 apiece) and most basic MERV-rated filters. Their purpose is to proceed particles larger than 10 microns—including pet pilus (but not dander), carpet fibers, and heavy dust—from bottleneck the heating/cooling coils and ducts in your HVAC system. They have little to no impact on fine particulates like pollen and smoke, then they will not practise much to ease respiratory issues. But even with their limitations, these filters aren't pointless. They prolong the life of your equipment and assistance keep it running efficiently in the heating and cooling seasons. "Think of how important your screen door is in summer when at that place's flies out," Owen said. If you are reading this guide, you lot probably care likewise much almost air quality to consider i of these filters, but if you're living (or vacationing) in a rental and don't want to invest much—specially if the existing filter is problematically old or muddied—replacing it with a MERV 1 to 4 filter would exist a fine quick fix.

• MERV 5 to 7: Owen said filters in this range (like this MERV 7 Nordic Pure) were created as an improvement on the bones MERV one to 4 filters and designed to also filter out midsize particles (iii to 10 microns, which includes most pollen and mold spores) that could encourage mold growth on heating/cooling coils. These filters are not every bit widely sold equally the lower and college MERV-rated filters in hardware stores, merely they can exist plant online easily. There's nil wrong with these types of filters; we just didn't focus on them as much equally we did those in the eight to 13 range more often than not because this course, past comparison, usually isn't any cheaper, doesn't perform quite every bit well, and often isn't equally easy to find.

• MERV 8 to xiii: This is the category nosotros'd recommend for people who care about indoor air quality, and in that location are many equally good examples, such equally the Nordic Pure MERV 10 and MERV 12, the Honeywell FPR 9, and the Filtrete 1500. (For more detail on these models, see the A perfectly proficient HVAC filter and Two other filters that are also fine sections.) Nosotros focused on filters in the MERV viii to 13 range considering they are skilful to excellent at removing fine particulates (as small-scale as 0.3 to 3.0 microns in diameter, including fume and frazzle particles and bacteria), plus anything larger. This MERV range, Owen said, "covers about of the stuff that people are likely to breathe in unless they're really close to the source." The EPA says filters rated MERV 7 to 13 "are likely to be nearly every bit effective every bit true HEPA filters at decision-making nigh airborne indoor particles." The higher end of the range, MERV 11 to 13, removes 20-plus to 50-plus percent of the very smallest, 0.3-to-1.0-micron particulates, and filters in this range are specially 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 14 through sixteen: These are specialized filters that require a purpose-built HVAC system; they're widely used in hospitals and some commercial and industrial environments, simply generally not in homes.

So why doesn't anybody get a MERV 8 to 13 filter? Beyond their college cost, there is besides a business your equipment might not be able to handle them, according 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 us MERV filters in this range restrict airflow more than low-MERV filters, as measured by the driblet in air pressure the filters create when installed. That can potentially strain your equipment.

Powell noted that, "You have a fair amount invested in your HVAC system, and unless you lot know how much pressure drop yous have in it and how much more information technology can handle, you could end up shortening the life of your blower. And a blower's not cheap." Ayers said, "That's the danger of looking at 1-inch filters and trying to become higher-efficiency and do the job that's needed for allergies: You lot run the risk of actually damaging your blower and your HVAC system." (If you lot are concerned about this, to exist absolutely punctilious you lot can rent an HVAC firm to mensurate pressure drop in your system.¹)

Confronting these warnings, however, is a mountain of owner testimony that MERV 11, 12, and fifty-fifty 13 filters accept worked just fine in their systems for years. Likewise, an often-cited comprehensive contained test of MERV 8 to 13 filters' effects on HVAC airflow and energy consumption (a proxy for how hard the equipment is working) concluded that fifty-fifty "if no accommodations are made for the greater pressure drop of high-MERV filters, air menstruum and energy penalties are not likely to be severe—at least, non until the filter is loaded with clay."

Nosotros feel the manufacturers' concerns are a bit overcautious, in part because a recent innovation in air filters permits loftier MERV ratings (11 to 13) with low pressure driblet.² So-chosen electret filters use a mat of fibers that are electrostatically charged. The charge helps concenter airborne particles (rather than just passively impeding them). As a result, the mat can be more than porous, causing ameliorate airflow and a smaller pressure level drop. All the same, Owen emphasized, electrets become less efficient over time, often significantly so. "Electret media volition drib in efficiency upon employ, sometimes by as much equally l percentage," she said. "Basically what happens is the tiny particles—nosotros're talking 40, fifty nanometers, which there are gazillions of in the air—will coat the charged fibers and keep them from attracting larger particles." That ways regularly replacing electrets is absolutely key to maintaining good filtration, and most come up with lx- or 90-twenty-four hours replacement schedules. If you run your organisation year-round, that's potentially vi filters a yr.

Given all this, nosotros decided that if we were ownership new filters today, we'd expect for an electret filter around the MERV viii to 13 level with a low pressure level drop that was both affordable and easy to find.

A perfectly skillful HVAC filter: Nordic Pure MERV 12

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

Nordic Pure MERV 12

Nordic Pure's MERV 12 filters are not the only products that meet all our criteria, only they are perfectly good examples, and they're usually competitively priced and easy to discover online. We similar that they're genuinely MERV-certified, because unlike the proprietary ratings used by some bigger-name brands, the MERV criteria are publicly available. 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 bacteria and fume; at least 80 percentage of 1.0-to-3.0-micron particles, which include fine grit and soot; and at least xc percent of larger pollen, grit, pet hair, and lint particles. Again, MERV stands for Minimum Efficiency Reporting Value, so this is the worst functioning measured during third-party testing to the ASHRAE 52.two standard. And again: the MERV exam measures a single pass of polluted air through the filter. In your habitation, the air will continuously recirculate when your HVAC organization 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 price than competitors—about $forty for a vi-pack of 16-by-25-by-one-inch filters, or almost $7 each (with some competitors you'll pay about double that toll for MERV eleven/12 or the equivalent). At the recommended three-calendar month replacement cycle, a Nordic Pure can relieve you about $thirty to $40 a twelvemonth.

Nordic Pure reports the filter's pressure level drop as 0.24 inch, which puts it a shade higher than the like, MERV 12–equivalent Filtrete 1500 at 0.22 inch. But most people seem to take had no issues with the Nordic Pures straining their HVAC organization—the vi-pack has an overall score of iv.3 stars (out of five) across more than 2,800 reviews at Amazon at this writing (we should note that the reviews once received an A rating from Fakespot; every bit of May 2019 that rating was downgraded to a C). The Nordic Pure MERV 12 filters are available in many sizes, so you should be able to find one that fits your return vent opening.

Two other filters that should do a fine job

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

If you can't find Nordic Pure in your size, or if you prefer to buy and pick upwardly a new filter in a store immediately, Honeywell'south FPR nine filters and Filtrete'south MPR 1500 filters are similar, and they're widely available at retail. (Dwelling Depot stocks Honeywell; Lowe'south and Ace stock Filtrete). These filters perform on a similar level as the Nordic Pure MERV 12, they are well-reviewed past 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 big advantage if yous need one ASAP.

Nosotros don't honey that neither Honeywell or Filtrete is MERV-certified, but their proprietary ratings are reportedly equivalent to MERV xi or 12. Nosotros couldn't notice force per unit area-drop information on the Honeywell, so that's a possible concern. The Filtrete'southward pressure drop is 0.22 inch, fractionally lower than the Nordic Pure MERV 12's at 0.24 inch. Data Filtrete shared with us indicates the the 1500 removed 54 percent of 0.3-to-i-micron particles in its own tests, versus a minimum of 35 percent for the MERV 12-certified Nordic Pure. On larger particles, the two filters performed very similarly.

A major reason nosotros'd expect for Nordic Pure as an option first comes downward to price: Both the Honeywell and Filtrete options usually cost more than than twice the cost of the Nordic Pure filters. As electret filters, all these models volition lose effectiveness every bit they capture particles, and should be replaced at least every three months, per the manufacturers' recommendation. Merely homes with certain challenging conditions—if y'all smoke, oftentimes use candles or fireplaces, or take pets—will significantly reduce that lifespan.³

Owen also offered a simple way to judge if it's time for a swap: "If you can get to your filter easily, i elementary thing you lot tin do is just become take a await. If you tin can't see the filter media anymore, it's been in in that location too long. Modify it!"

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

During a wildfire, you'll need to modify your filters more than ofttimes than y'all would nether normal air conditions, and at that place are a few indicators that can aid you lot know when it's time to replace one.

We asked Kathleen Owen, the filtration adept nosotros 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 cost prohibitive, I'd probably modify a iii-month filter every month during the season. Or possibly after each major event— say if a fire gets shut plenty to be a large deal (rather than simply you know almost information technology from the news)."

Owen too noted that wildfire fume is a circuitous mixture, incorporating both physical smoke particles (which filters trap permanently) and h2o vapor and volatile organic compounds (gases), which are non trapped—and the latter of which create the smoky scent. "The wet particles or ones with gases adsorbed on them tin be collected, then give off the evil-smelling stuff the next time the fan comes on," she wrote. "And so, one recommendation is that if folks feel like the air breathes easier or smells OK with the HVAC on only are gagging in the first minute or two the HVAC is on again, irresolute the filter could aid."

There are also visual cues you tin await for when judging whether to supersede your furnace filter, Owen wrote. Bottleneck increases the pressure level differential between the intake and outflow sides, and this can cause the filter'southward pleats to flatten out or the frame of the filter to buckle. Both are evidence that the smoky air is finding a path around the chock-full filter rather than through it, and that it'south fourth dimension to install a new one.

In improver to obvious steps like keeping windows and doors airtight, Owen too advised shutting off bathroom fans and range hoods, both of which vent direct to the outside and, as a result, draw an equal book 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 confronting an extreme load of ethanol vapors nosotros institute most of them ineffective, anecdotally we tin say that they seem to perform well under fairly heavy smoke conditions. Both in guide author Tim Heffernan's flat and in our New York test space, after running our top picks for a few hours, at that place was little olfactory evidence that hundreds of matches had been burned nearby.

Finally, Owen noted that the American Social club of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) has begun working on building-filtration guidelines specific to wildfire weather. Nosotros'll be following up on this equally it develops. For more than on this topic, delight see our reporting on how to clean wildfire smoke from your abode.