Can I Use 20x20x1 Furnace Filters To Replace

The inquiry

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
2 other filters that should exercise a fine job
How oft should I supplant my filters during wildfire smoke events?
Footnotes

Who this is for

Most HVAC systems employ a standard one-inch-thick filter, then nosotros focused exclusively on one-inch medium-efficiency MERV filters. These are installed either in wall-mounted air-return vents (most common in the Southward), or at the air handler (more mutual in the Mid-Atlantic and northern states, where the air handler is oftentimes placed in the basement, near the furnace). A correctly sized 1-inch MERV filter simply rests backside a bracket at the return register; if you're not sure what size you need, check the narrow side of an existing filter for the dimensions (like "16 10 25 10 one").

If your HVAC arrangement uses a thicker filter (usually in the 4- to 5-inch range, and commonly mounted at the air handler), it was likely designed specifically for medium-efficiency MERV filtration. You lot don't need our advice; just 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 measure of how well a filter removes particulates from the air. In that way it'south alike 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 percentage of particles information technology captures—in a unmarried pass. Air is loaded with particulate matter, sent through the filter a single fourth dimension, and the results measured. In real-earth use, with the air in your dwelling house 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 fundamental ways. Commencement, instead of being a simple pass-fail measure like HEPA (a filter is either HEPA-rated or it's not), MERV ratings fall on a calibration from 1 to 16, with higher numbers indicating better functioning.

Besides dissimilar HEPA, MERV tests mensurate particulates of different sizes, from 0.iii micron (very small and difficult to filter—the size HEPA tests measure) up to 10 microns (relatively large and easy to filter). MERV besides doesn't accept a target percentage for removal, the style HEPA does. Instead, the actual percent removal is recorded for each of 12 particle sizes, and these numbers are referenced confronting a operation tabular array to determine the appropriate rating.

So when you wait at the full spectrum of what's floating effectually in the air in your house, MERV ratings reflect a filter'due south operation on all of information technology. College numbers signal a better filtration of the smaller particles, like pollen and fume, that cause many respiratory issues. And medium-efficiency MERV filters in the eight to 13 range—the kind we would go—can remove xc percent or more of these. (For a actually thorough explanation of how MERV ratings are calculated, visit the website of the National Air Filtration Association.)

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

Subsequently we inquired, Filtrete replied that its MPR filters capture more of the very minor particles (0.three 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 (1 to 10 or more microns), MERV and MPR operation was about identical. Filtrete said MPR 1900 is equivalent to MERV 13, MPR 1500 to MERV 12, and MPR 1000 to MERV xi.

Dwelling Depot shared a basic comparative chart just no test data or protocols; it equates FPR 9 and 10 to MERV 12, FPR vii and 8 to MERV 11, and FPR half-dozen to MERV ten.

How to choose a filter by its MERV rating

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

To decide what filter we'd buy, nosotros needed a more pragmatic caption of MERV, then we turned to Kathleen Owen, a research engineer specializing in air filtration. Owen most literally wrote the volume on MERV: In the 1990s she helped define the American Club of Heating, Refrigeration, and Ac Engineers's ASHRAE 52.2 standard that'due south used to set the ratings. She after chaired the ASHRAE 52.2 committee, which regularly updates the standard to accost changes in filter applied science.

In a conversation almost the virtually common filter levels for sale at retail, MERV 1 through 16, Owen said this range "gets y'all from filters that might grab a golf ball—I'm exaggerating a little bit—up to filters that will 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 two True Blue, MERV 1 Filtrete Basic Cut-To-Fit, and the unrated Flanders, are the cheapest (some under $1 apiece) and most bones MERV-rated filters. Their purpose is to go on particles larger than 10 microns—including pet hair (only non dander), carpet fibers, and heavy dust—from clogging the heating/cooling coils and ducts in your HVAC organization. They have little to no impact on fine particulates like pollen and smoke, so they will not do 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. "Call up of how important your screen door is in summer when there's flies out," Owen said. If you are reading this guide, y'all probably care too much nigh 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—peculiarly if the existing filter is problematically old or dingy—replacing it with a MERV 1 to 4 filter would be a fine quick fix.

• MERV v to 7: Owen said filters in this range (similar this MERV vii Nordic Pure) were created as an improvement on the basic MERV i to 4 filters and designed to also filter out midsize particles (3 to x microns, which includes most pollen and mold spores) that could encourage mold growth on heating/cooling coils. These filters are non as widely sold equally the lower and college MERV-rated filters in hardware stores, but they can exist found online easily. At that place'due south cypher wrong with these types of filters; nosotros just didn't focus on them as much as nosotros did those in the eight to xiii range mostly considering this class, past comparison, usually isn't any cheaper, doesn't perform quite also, and often isn't as easy to find.

• MERV 8 to 13: This is the category nosotros'd recommend for people who intendance nearly indoor air quality, and in that location are many equally proficient examples, such as the Nordic Pure MERV 10 and MERV 12, the Honeywell FPR ix, and the Filtrete 1500. (For more detail on these models, see the A perfectly good HVAC filter and Ii other filters that are also fine sections.) We focused on filters in the MERV eight to 13 range because they are skilful to fantabulous at removing fine particulates (every bit minor as 0.3 to 3.0 microns in diameter, including fume and exhaust particles and bacteria), plus anything larger. This MERV range, Owen said, "covers most of the stuff that people are probable to exhale in unless they're really close to the source." The EPA says filters rated MERV 7 to 13 "are likely to be well-nigh equally effective as true HEPA filters at controlling virtually 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.three-to-ane.0-micron particulates, and filters in this range are especially popular. An NIH literature review indicates that filters in this range can significantly reduce indoor fine-particulate pollution and alleviate some respiratory ailments.

• MERV 14 through 16: These are specialized filters that crave a purpose-congenital HVAC organization; they're widely used in hospitals and some commercial and industrial environments, but generally not in homes.

So why doesn't anybody get a MERV 8 to xiii filter? Across their higher toll, there is likewise a concern your equipment might non be able to handle them, according to engineers nosotros 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 drop in air pressure the filters create when installed. That can potentially strain your equipment.

Powell noted that, "You have a fair corporeality invested in your HVAC system, and unless y'all know how much pressure drop you have in it and how much more information technology can handle, yous could terminate upwards shortening the life of your blower. And a blower's not inexpensive." Ayers said, "That's the danger of looking at 1-inch filters and trying to go higher-efficiency and do the job that's needed for allergies: You run the risk of really damaging your blower and your HVAC system." (If yous are concerned about this, to exist absolutely punctilious you tin can hire an HVAC firm to measure pressure drop in your system.ⁱ)

Confronting these warnings, however, is a mountain of owner testimony that MERV 11, 12, and even 13 filters have worked just fine in their systems for years. As well, an oft-cited comprehensive independent test of MERV viii to thirteen 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 driblet of high-MERV filters, air flow and energy penalties are non likely to be severe—at to the lowest degree, non until the filter is loaded with dirt."

We feel the manufacturers' concerns are a bit overcautious, in role because a recent innovation in air filters permits high MERV ratings (11 to thirteen) with low force per unit area drop.ⁱⁱ So-called electret filters employ 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 porous, causing better airflow and a smaller pressure drop. Withal, Owen emphasized, electrets go less efficient over fourth dimension, often significantly so. "Electret media volition drop in efficiency upon use, sometimes by as much as 50 percent," she said. "Basically what happens is the tiny particles—we're talking 40, 50 nanometers, which there are gazillions of in the air—volition coat the charged fibers and keep them from attracting larger particles." That means regularly replacing electrets is admittedly central to maintaining good filtration, and most come with lx- or ninety-twenty-four hours replacement schedules. If you run your arrangement yr-round, that'south potentially six filters a year.

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

A perfectly good 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'south MERV 12 filters are not the only products that meet all our criteria, but they are perfectly good examples, and they're usually competitively priced and easy to find 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 volition remove at to the lowest degree 35 pct of particles in the 0.3-to-1.0-micron range, which includes bacteria and fume; at least 80 percent of 1.0-to-iii.0-micron particles, which include fine dust and soot; and at least 90 pct of larger pollen, dust, pet hair, and lint particles. Again, MERV stands for Minimum Efficiency Reporting Value, so this is the worst performance measured during 3rd-political party testing to the ASHRAE 52.2 standard. And again: the MERV test measures a unmarried pass of polluted air through the filter. In your dwelling, 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 price than competitors—near $40 for a six-pack of 16-by-25-by-1-inch filters, or about $seven each (with some competitors you'll pay about double that price for MERV eleven/12 or the equivalent). At the recommended 3-month replacement bike, a Nordic Pure can save you about $30 to $40 a year.

Nordic Pure reports the filter's pressure drop as 0.24 inch, which puts it a shade college than the similar, MERV 12–equivalent Filtrete 1500 at 0.22 inch. But nearly people seem to have had no problems with the Nordic Pures straining their HVAC system—the six-pack has an overall score of 4.3 stars (out of five) across more than than ii,800 reviews at Amazon at this writing (we should note that the reviews one time received an A rating from Fakespot; as of May 2019 that rating was downgraded to a C). The Nordic Pure MERV 12 filters are bachelor in many sizes, and 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 discover Nordic Pure in your size, or if yous prefer to buy and pick upward a new filter in a store immediately, Honeywell's FPR 9 filters and Filtrete's 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 similar level as the Nordic Pure MERV 12, they are well-reviewed by many owners, they come in a wide range of sizes, and the loftier likelihood that they're in stock at a nearby hardware store is a big advantage if you demand one ASAP.

We don't love that neither Honeywell or Filtrete is MERV-certified, simply their proprietary ratings are reportedly equivalent to MERV xi or 12. We couldn't find pressure-driblet information on the Honeywell, so that'due south a possible concern. The Filtrete'south pressure drop is 0.22 inch, fractionally lower than the Nordic Pure MERV 12's at 0.24 inch. Data Filtrete shared with usa indicates the the 1500 removed 54 percentage of 0.three-to-1-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 look for Nordic Pure equally an option starting time comes down to cost: Both the Honeywell and Filtrete options ordinarily toll more than than twice the price of the Nordic Pure filters. Every bit electret filters, all these models will lose effectiveness as they capture particles, and should exist replaced at least every 3 months, per the manufacturers' recommendation. But homes with certain challenging weather—if you smoke, frequently use candles or fireplaces, or have pets—will significantly reduce that lifespan.³

Owen also offered a unproblematic way to gauge if it'due south time for a swap: "If you can get to your filter easily, i elementary thing you tin can do is simply go take a expect. If you can't run into the filter media anymore, it'south been in there too long. Change it!"

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

During a wildfire, y'all'll demand to change your filters more than often than you would under normal air conditions, and there are a few indicators that tin help you know when information technology'south time to replace one.

We asked Kathleen Owen, the filtration expert we spoke with for this guide, for her advice. She replied in an email: "If I lived most the wildfires and didn't find the toll prohibitive, I'd probably modify a 3-month filter every month during the flavor. Or possibly after each major consequence— say if a fire gets close enough to exist a big deal (rather than merely you know about information technology from the news)."

Owen as well noted that wildfire smoke is a complex mixture, incorporating both physical fume particles (which filters trap permanently) and water vapor and volatile organic compounds (gases), which are not trapped—and the latter of which create the smoky odour. "The wet particles or ones with gases adsorbed on them can be collected, then give off the smelly stuff the next fourth dimension the fan comes on," she wrote. "So, one recommendation is that if folks feel like the air breathes easier or smells OK with the HVAC on but are gagging in the first minute or two the HVAC is on again, irresolute the filter could help."

At that place are besides visual cues you can look for when judging whether to supplant your furnace filter, Owen wrote. Clogging increases the pressure differential betwixt the intake and outflow sides, and this tin can crusade the filter'south pleats to flatten out or the frame of the filter to buckle. Both are prove 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 1.

In addition to obvious steps like keeping windows and doors closed, Owen also brash shutting off bathroom fans and range hoods, both of which vent direct to the outside and, equally a effect, describe 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 found about of them ineffective, anecdotally we can say that they seem to perform well under fairly heavy smoke conditions. Both in guide writer Tim Heffernan'due south apartment and in our New York test space, later running our top picks for a few hours, there was lilliputian olfactory evidence that hundreds of matches had been burned nearby.

Finally, Owen noted that the American Gild of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) has begun working on building-filtration guidelines specific to wildfire conditions. We'll be following upwardly on this equally it develops. For more than on this topic, please come across our reporting on how to clean wildfire smoke from your home.

Footnotes