What Does Furnace Manufactures Recommend On Merv Rating Filters For Equipment

The research

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

Who this is for

Virtually HVAC systems use a standard 1-inch-thick filter, so nosotros focused exclusively on 1-inch medium-efficiency MERV filters. These are installed either in wall-mounted air-return vents (most common in the S), or at the air handler (more common in the Mid-Atlantic and northern states, where the air handler is ofttimes placed in the basement, near the furnace). A correctly sized i-inch MERV filter simply rests behind a subclass at the render register; if you're not certain what size you demand, bank check the narrow side of an existing filter for the dimensions (like "16 x 25 x i").

If your HVAC arrangement uses a thicker filter (normally in the four- to 5-inch range, and normally mounted at the air handler), it was likely designed specifically for medium-efficiency MERV filtration. You don't need our advice; only 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's 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 percentage of particles it captures—in a unmarried pass. Air is loaded with particulate matter, sent through the filter a single time, and the results measured. In real-world use, 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.

Simply MERV is different in some central means. First, instead of being a simple pass-fail measure like HEPA (a filter is either HEPA-rated or information technology's not), MERV ratings fall on a calibration from 1 to 16, with higher numbers indicating better operation.

Likewise unlike HEPA, MERV tests measure particulates of different sizes, from 0.iii micron (very minor and difficult to filter—the size HEPA tests measure out) upwards to 10 microns (relatively large and like shooting fish in a barrel to filter). MERV as well doesn't have a target pct for removal, the style HEPA does. Instead, the bodily percent removal is recorded for each of 12 particle sizes, and these numbers are referenced against a performance tabular array to make up one's mind the advisable rating.

So when you look at the full spectrum of what's floating around in the air in your house, MERV ratings reflect a filter'southward operation on all of it. Higher numbers indicate a better filtration of the smaller particles, like pollen and smoke, that crusade many respiratory bug. And medium-efficiency MERV filters in the viii to 13 range—the kind we would get—can remove 90 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.)

Ane 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 past Abode Depot). Both merits to be based on the American Order of Heating, Refrigeration, and Ac Engineers's ASHRAE 52.ii standard that's used to set MERV ratings, but neither company provides an easily attainable 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 actually got 1 in your hands.)

After we inquired, Filtrete replied that its MPR filters capture more than of the very small particles (0.3 to 1 micron) than equivalent MERV-rated filters when tested to ASHRAE 52.ii protocol, and shared a exam summary that backs this upward; on the larger particles (1 to 10 or more microns), MERV and MPR performance was nearly identical. Filtrete said MPR 1900 is equivalent to MERV 13, MPR 1500 to MERV 12, and MPR chiliad to MERV 11.

Home Depot shared a basic comparative chart but no test information or protocols; it equates FPR 9 and 10 to MERV 12, FPR 7 and viii to MERV xi, and FPR half dozen to MERV 10.

How to choose a filter by its MERV rating

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

To make up one's mind what filter we'd buy, we needed a more businesslike caption of MERV, so we turned to Kathleen Owen, a research engineer specializing in air filtration. Owen almost literally wrote the volume on MERV: In the 1990s she helped define the American Social club of Heating, Refrigeration, and Air-Workout Engineers's ASHRAE 52.2 standard that's used to set up the ratings. She afterward chaired the ASHRAE 52.ii committee, which regularly updates the standard to address changes in filter technology.

In a conversation most the near common filter levels for auction at retail, MERV 1 through xvi, Owen said this range "gets you from filters that might take hold of a golf ball—I'yard exaggerating a petty bit—upwardly to filters that will grab almost everything." Owen added, "I like to tell people that each of those filters has a purpose."

• MERV 1 to 4 (and unrated): Filters similar the MERV 4 East-Z Flow, MERV 2 True Blue, MERV 1 Filtrete Bones Cut-To-Fit, and the unrated Flanders, are the cheapest (some under $1 apiece) and most bones MERV-rated filters. Their purpose is to keep particles larger than 10 microns—including pet hair (but not dander), rug fibers, and heavy grit—from bottleneck the heating/cooling coils and ducts in your HVAC system. They have little to no impact on fine particulates similar pollen and fume, then they will not do much to ease respiratory problems. But even with their limitations, these filters aren't pointless. They prolong the life of your equipment and aid keep it running efficiently in the heating and cooling seasons. "Think of how of import your screen door is in summer when there's flies out," Owen said. If you are reading this guide, yous probably care too much about air quality to consider one of these filters, only if you're living (or vacationing) in a rental and don't want to invest much—especially if the existing filter is problematically old or muddied—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 (like this MERV vii Nordic Pure) were created equally an comeback on the bones MERV 1 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 not as widely sold equally the lower and higher MERV-rated filters in hardware stores, but they tin can exist found online hands. In that location'south nothing wrong with these types of filters; we only didn't focus on them as much every bit we did those in the viii to 13 range generally because this form, by comparison, ordinarily isn't whatever cheaper, doesn't perform quite every bit well, and often isn't as piece of cake to find.

• MERV eight to 13: This is the category nosotros'd recommend for people who care about indoor air quality, and there are many equally good examples, such every bit 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 good HVAC filter and Two other filters that are too fine sections.) We focused on filters in the MERV viii to 13 range because they are good to excellent at removing fine particulates (equally small every bit 0.3 to 3.0 microns in diameter, including fume and exhaust particles and leaner), plus anything larger. This MERV range, Owen said, "covers most of the stuff that people are likely to breathe in unless they're really shut to the source." The EPA says filters rated MERV 7 to thirteen "are probable to exist well-nigh as effective as true HEPA filters at decision-making nigh airborne indoor particles." The higher end of the range, MERV 11 to 13, removes 20-plus to l-plus percent of the very smallest, 0.iii-to-1.0-micron particulates, and filters in this range are specially 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 require a purpose-built HVAC organisation; they're widely used in hospitals and some commercial and industrial environments, but mostly not in homes.

So why doesn't everyone get a MERV 8 to thirteen filter? Across their higher cost, in that location is as well a concern 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 usa MERV filters in this range restrict airflow more than low-MERV filters, as measured by the drop in air pressure level the filters create when installed. That tin can potentially strain your equipment.

Powell noted that, "You have a fair amount invested in your HVAC system, and unless yous know how much pressure drib you lot take in it and how much more it tin handle, you could cease up shortening the life of your blower. And a blower'south non cheap." Ayers said, "That'southward the danger of looking at 1-inch filters and trying to go higher-efficiency and practise the task that's needed for allergies: Yous run the risk of really damaging your blower and your HVAC system." (If you are concerned about this, to be absolutely punctilious you can hire an HVAC firm to mensurate pressure drib in your organisation.¹)

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 often-cited comprehensive independent exam of MERV 8 to 13 filters' effects on HVAC airflow and energy consumption (a proxy for how hard the equipment is working) concluded that even "if no accommodations are fabricated for the greater pressure drop of high-MERV filters, air flow and energy penalties are non probable to be severe—at to the lowest degree, not until the filter is loaded with clay."

We feel the manufacturers' concerns are a chip overcautious, in part considering a recent innovation in air filters permits high MERV ratings (xi to 13) with low pressure level drib.^two Then-called electret filters use a mat of fibers that are electrostatically charged. The charge helps attract airborne particles (rather than just passively impeding them). As a issue, the mat can be more porous, causing improve airflow and a smaller pressure level drop. All the same, Owen emphasized, electrets get less efficient over time, often significantly then. "Electret media will drop in efficiency upon use, sometimes past as much as 50 percent," she said. "Basically what happens is the tiny particles—we're talking twoscore, 50 nanometers, which at that place are gazillions of in the air—volition coat the charged fibers and keep them from attracting larger particles." That ways regularly replacing electrets is absolutely fundamental to maintaining adept filtration, and nigh come up with 60- or ninety-day replacement schedules. If you run your system yr-round, that's potentially half dozen filters a yr.

Given all this, nosotros decided that if we were ownership new filters today, nosotros'd look for an electret filter around the MERV 8 to 13 level with a depression pressure drop that was both affordable and easy to find.

A perfectly skilful 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, simply they are perfectly good examples, and they're normally competitively priced and easy to find online. We like 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.iii-to-ane.0-micron range, which includes leaner and smoke; at least eighty percent of one.0-to-iii.0-micron particles, which include fine dust and soot; and at to the lowest degree 90 pct of larger pollen, dust, pet hair, and lint particles. Again, MERV stands for Minimum Efficiency Reporting Value, so this is the worst operation 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 habitation, the air will continuously recirculate when your HVAC arrangement is, leading to cumulatively greater filtration with each trip through the render registers.

Nordic Pure filters are by and large sold online, and the MERV 12s typically retail for a much lower price than competitors—almost $40 for a half dozen-pack of 16-by-25-past-one-inch filters, or about $seven each (with some competitors you'll pay about double that price for MERV 11/12 or the equivalent). At the recommended iii-month replacement wheel, a Nordic Pure can save you almost $30 to $40 a yr.

Nordic Pure reports the filter's force per unit area drop every bit 0.24 inch, which puts information technology a shade higher than the similar, MERV 12–equivalent Filtrete 1500 at 0.22 inch. But most people seem to have had no issues with the Nordic Pures straining their HVAC system—the six-pack has an overall score of 4.3 stars (out of five) beyond more than than ii,800 reviews at Amazon at this writing (nosotros should annotation that the reviews in one case 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, so you lot should be able to find i that fits your return vent opening.

2 other filters that should exercise a fine chore

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

If you can't detect Nordic Pure in your size, or if you prefer to buy and pick up a new filter in a shop immediately, Honeywell's FPR 9 filters and Filtrete's MPR 1500 filters are like, and they're widely bachelor at retail. (Home Depot stocks Honeywell; Lowe'southward 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 up 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 ane ASAP.

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

A major reason we'd look for Nordic Pure as an option first comes down to price: Both the Honeywell and Filtrete options usually cost more than twice the price of the Nordic Pure filters. As electret filters, all these models will lose effectiveness as they capture particles, and should exist replaced at to the lowest degree every iii months, per the manufacturers' recommendation. But homes with certain challenging conditions—if yous smoke, oftentimes use candles or fireplaces, or take pets—will significantly reduce that lifespan.³

Owen likewise offered a simple way to estimate if information technology's fourth dimension for a swap: "If you can become to your filter easily, one elementary thing you can do is just go have a look. If you can't come across the filter media anymore, it's been in there too long. Change information technology!"

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

During a wildfire, you lot'll need to change your filters more often than you would under normal air conditions, and there are a few indicators that can assistance you know when it's time to supercede ane.

Nosotros asked Kathleen Owen, the filtration expert nosotros spoke with for this guide, for her communication. She replied in an e-mail: "If I lived near the wildfires and didn't observe the cost prohibitive, I'd probably alter a 3-month filter every month during the flavor. Or perhaps after each major event— say if a burn gets close enough to be a big deal (rather than simply you lot know about information technology from the news)."

Owen also 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 not trapped—and the latter of which create the smoky scent. "The wet particles or ones with gases adsorbed on them tin be collected, and so give off the smelly 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 just are gagging in the beginning minute or two the HVAC is on over again, changing the filter could assistance."

There are also visual cues you lot can expect for when judging whether to replace your furnace filter, Owen wrote. Bottleneck increases the pressure differential between the intake and outflow sides, and this tin can cause the filter's 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 clogged filter rather than through information technology, 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 directly to the outside and, as a consequence, describe 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 against an extreme load of ethanol vapors we establish virtually of them ineffective, anecdotally nosotros can say that they seem to perform well nether adequately heavy smoke weather. Both in guide writer Tim Heffernan'due south flat and in our New York test space, after running our meridian 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 Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) has begun working on building-filtration guidelines specific to wildfire conditions. We'll be following upwards on this as it develops. For more than on this topic, please see our reporting on how to make clean wildfire smoke from your home.

Footnotes