What Merv Filter Is Best For Hvac?

The enquiry

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 frequently should I replace my filters during wildfire fume events?
Footnotes

Who this is for

Nearly HVAC systems use a standard 1-inch-thick filter, and then we focused exclusively on 1-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 common in the Mid-Atlantic and northern states, where the air handler is oftentimes placed in the basement, well-nigh the furnace). A correctly sized 1-inch MERV filter merely rests behind a bracket at the render register; 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 (ordinarily in the four- to 5-inch range, and normally mounted at the air handler), information technology was likely designed specifically for medium-efficiency MERV filtration. You don't need our advice; simply supersede 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 out 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 examination for HEPA rating, MERV testing measure a filter's efficiency—the pct of particles information technology captures—in a single laissez passer. Air is loaded with particulate affair, sent through the filter a single time, and the results measured. In real-world 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 different in some primal means. First, instead of being a elementary pass-fail measure out like HEPA (a filter is either HEPA-rated or it's not), MERV ratings fall on a scale from 1 to sixteen, with higher numbers indicating meliorate functioning.

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) upwards to x microns (relatively large and easy to filter). MERV likewise doesn't take a target percentage for removal, the way HEPA does. Instead, the actual per centum removal is recorded for each of 12 particle sizes, and these numbers are referenced against a performance table to determine the appropriate rating.

So when you look at the full spectrum of what'south floating around in the air in your house, MERV ratings reverberate a filter'south operation 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 nosotros would become—can 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 than affair: Some companies, including major filter manufacturer 3M/Filtrete and major filter retailer Dwelling house Depot, use their ain rating conventions (MPR by Filtrete and FPR past Domicile Depot). Both claim to be based on the American Society of Heating, Refrigeration, and Ac Engineers's ASHRAE 52.2 standard that's used to fix MERV ratings, but neither visitor provides an easily accessible explanation of how its own ratings differ from or compare with MERV. (Filtrete does impress MPR and MERV equivalents on the frames of its filters, but y'all can't meet that until you've really got one in your hands.)

After nosotros inquired, Filtrete replied that its MPR filters capture more of the very small particles (0.3 to 1 micron) than equivalent MERV-rated filters when tested to ASHRAE 52.two protocol, and shared a test summary that backs this up; on the larger particles (1 to 10 or more microns), MERV and MPR performance was almost identical. Filtrete said MPR 1900 is equivalent to MERV thirteen, MPR 1500 to MERV 12, and MPR g to MERV 11.

Dwelling Depot shared a bones comparative nautical chart simply no test data or protocols; it equates FPR 9 and x to MERV 12, FPR vii and 8 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 — Photo: Michael Hession

To determine what filter we'd buy, nosotros needed a more pragmatic explanation of MERV, and then we turned to Kathleen Owen, a research engineer specializing in air filtration. Owen almost literally wrote the book on MERV: In the 1990s she helped ascertain the American Society of Heating, Refrigeration, and Air-Conditioning Engineers's ASHRAE 52.2 standard that's used to gear up the ratings. She subsequently chaired the ASHRAE 52.two commission, which regularly updates the standard to accost changes in filter engineering science.

In a conversation about the near common filter levels for sale at retail, MERV i through sixteen, Owen said this range "gets you from filters that might take hold of a golf ball—I'thousand exaggerating a little bit—up to filters that will catch almost everything." Owen added, "I similar to tell people that each of those filters has a purpose."

• MERV i to 4 (and unrated): Filters like the MERV 4 E-Z Catamenia, MERV ii True Blue, MERV 1 Filtrete Bones Cut-To-Fit, and the unrated Flemish region, are the cheapest (some under $one apiece) and most basic MERV-rated filters. Their purpose is to keep particles larger than 10 microns—including pet hair (but not dander), carpet fibers, and heavy grit—from clogging the heating/cooling coils and ducts in your HVAC system. They have piddling to no impact on fine particulates like pollen and smoke, and so they will not do much to ease respiratory bug. 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. "Recall of how important your screen door is in summer when at that place's flies out," Owen said. If you are reading this guide, y'all probably care likewise much about air quality to consider one of these filters, but if you're living (or vacationing) in a rental and don't want to invest much—especially if the existing filter is problematically quondam or dirty—replacing it with a MERV i to 4 filter would be a fine quick set.

• MERV five to 7: Owen said filters in this range (similar this MERV vii Nordic Pure) were created as an comeback on the basic MERV 1 to iv filters and designed to also filter out midsize particles (3 to ten microns, which includes well-nigh 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, only they can exist institute online hands. There's cipher wrong with these types of filters; we just didn't focus on them every bit much as we did those in the viii to 13 range by and large because this class, past comparison, usually isn't any cheaper, doesn't perform quite too, and frequently isn't as piece of cake to find.

• MERV eight to 13: This is the category we'd recommend for people who intendance most indoor air quality, and there are many equally proficient 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 Ii other filters that are besides fine sections.) Nosotros focused on filters in the MERV 8 to 13 range because they are good to excellent at removing fine particulates (as small equally 0.3 to iii.0 microns in diameter, including fume and exhaust particles and bacteria), plus anything larger. This MERV range, Owen said, "covers well-nigh of the stuff that people are likely to breathe in unless they're actually close to the source." The EPA says filters rated MERV vii to xiii "are likely to be nearly as effective every bit truthful HEPA filters at controlling about airborne indoor particles." The higher cease of the range, MERV eleven to 13, removes xx-plus to 50-plus per centum of the very smallest, 0.3-to-1.0-micron particulates, and filters in this range are especially pop. 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-congenital HVAC system; they're widely used in hospitals and some commercial and industrial environments, but generally not in homes.

Then why doesn't anybody get a MERV 8 to thirteen filter? Across their higher cost, there is also a concern your equipment might not be able to handle them, according to engineers nosotros interviewed from 2 of the major HVAC manufacturers: Jay Ayers of Trane and Doug Powell of Carrier. They (and Owen) all told the states MERV filters in this range restrict airflow more low-MERV filters, as measured by the drop in air force per unit area the filters create when installed. That can potentially strain your equipment.

Powell noted that, "You have a off-white amount invested in your HVAC system, and unless you know how much pressure drib y'all accept in it and how much more it tin handle, you could end up shortening the life of your blower. And a blower'south non cheap." Ayers said, "That'south the danger of looking at ane-inch filters and trying to go higher-efficiency and do the task that'southward needed for allergies: Yous run the risk of really damaging your blower and your HVAC system." (If yous are concerned well-nigh this, to be absolutely punctilious you can rent an HVAC business firm to measure pressure drop in your system.^one)

Confronting these warnings, however, is a mountain of owner testimony that MERV 11, 12, and even xiii filters have worked only fine in their systems for years. Every bit well, an often-cited comprehensive independent 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 even "if no accommodations are made for the greater pressure drop of high-MERV filters, air flow and energy penalties are not likely to be astringent—at least, not until the filter is loaded with dirt."

Nosotros feel the manufacturers' concerns are a scrap overcautious, in part because a recent innovation in air filters permits high MERV ratings (11 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 just passively impeding them). Equally a event, the mat can be more porous, causing better airflow and a smaller pressure driblet. Still, Owen emphasized, electrets become less efficient over time, often significantly and so. "Electret media will drop in efficiency upon use, sometimes by as much equally 50 per centum," she said. "Basically what happens is the tiny particles—nosotros're talking xl, fifty nanometers, which at that place are gazillions of in the air—will coat the charged fibers and keep them from alluring larger particles." That means regularly replacing electrets is admittedly key to maintaining good filtration, and almost come with 60- or 90-day replacement schedules. If you lot run your system twelvemonth-round, that'southward potentially six filters a year.

Given all this, nosotros decided that if we were buying new filters today, nosotros'd wait for an electret filter around the MERV 8 to 13 level with a low pressure drop that was both affordable and easy 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's MERV 12 filters are not the simply products that meet all our criteria, simply they are perfectly good examples, and they're usually competitively priced and easy to find online. We like 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 pct of particles in the 0.3-to-1.0-micron range, which includes bacteria and smoke; at to the lowest degree fourscore per centum of i.0-to-3.0-micron particles, which include fine dust and soot; and at to the lowest degree 90 percent 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 tertiary-party testing to the ASHRAE 52.2 standard. And once again: the MERV test measures a single pass of polluted air through the filter. In your home, the air volition 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—nigh $40 for a six-pack of sixteen-past-25-past-1-inch filters, or nigh $7 each (with some competitors you lot'll pay almost double that price for MERV 11/12 or the equivalent). At the recommended iii-month replacement wheel, a Nordic Pure can save you well-nigh $xxx to $xl a year.

Nordic Pure reports the filter'southward pressure drop equally 0.24 inch, which puts it a shade higher than the similar, MERV 12–equivalent Filtrete 1500 at 0.22 inch. Only most people seem to have had no issues with the Nordic Pures straining their HVAC organisation—the six-pack has an overall score of 4.three stars (out of 5) across more than 2,800 reviews at Amazon at this writing (we should notation that the reviews once received an A rating from Fakespot; equally of May 2019 that rating was downgraded to a C). The Nordic Pure MERV 12 filters are available in many sizes, so y'all should be able to notice ane 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 yous can't find Nordic Pure in your size, or if y'all prefer to buy and pick up 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 past many owners, they come in a broad range of sizes, and the high likelihood that they're in stock at a nearby hardware store is a big advantage if you need one ASAP.

We don't love that neither Honeywell or Filtrete is MERV-certified, but their proprietary ratings are reportedly equivalent to MERV 11 or 12. We couldn't find pressure level-drop data on the Honeywell, so that'southward a possible business. The Filtrete's force per unit area drop is 0.22 inch, fractionally lower than the Nordic Pure MERV 12'southward at 0.24 inch. Data Filtrete shared with the states indicates the the 1500 removed 54 pct 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 ii filters performed very similarly.

A major reason we'd look for Nordic Pure as an option starting time comes downwards to price: Both the Honeywell and Filtrete options usually cost more twice the price of the Nordic Pure filters. As electret filters, all these models will lose effectiveness every bit they capture particles, and should be replaced at least every three months, per the manufacturers' recommendation. Only homes with certain challenging conditions—if you fume, frequently use candles or fireplaces, or have pets—will significantly reduce that lifespan.³

Owen also offered a simple style to gauge if information technology's time for a swap: "If you can get to your filter easily, i unproblematic thing you tin can do is just get take a look. If you can't meet the filter media anymore, it'southward been in there as well long. Change it!"

How frequently should I replace my filters during wildfire fume events?

During a wildfire, you'll need to change your filters more often than you would nether normal air conditions, and at that place are a few indicators that can help you know when it's time to replace ane.

Nosotros asked Kathleen Owen, the filtration expert we spoke with for this guide, for her communication. She replied in an email: "If I lived near the wildfires and didn't find the cost prohibitive, I'd probably change a three-month filter every month during the season. Or mayhap subsequently each major upshot— say if a fire gets close plenty to be a big deal (rather than simply y'all know nearly information technology from the news)."

Owen also noted that wildfire smoke is a circuitous mixture, incorporating both physical smoke particles (which filters trap permanently) and h2o vapor and volatile organic compounds (gases), which are not trapped—and the latter of which create the smoky odor. "The wet particles or ones with gases adsorbed on them can be nerveless, then give off the smelly stuff the side by side time 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 commencement minute or 2 the HVAC is on again, changing the filter could assistance."

At that place are also visual cues you tin can expect for when judging whether to supercede your furnace filter, Owen wrote. Clogging increases the pressure level differential between the intake and outflow sides, and this tin can crusade 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 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 as well advised shutting off bathroom fans and range hoods, both of which vent directly to the outside and, as a result, draw 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 accept them, and though in our tests against an extreme load of ethanol vapors we institute about of them ineffective, anecdotally nosotros can say that they seem to perform well under fairly heavy smoke conditions. Both in guide author Tim Heffernan's apartment and in our New York test space, after running our height picks for a few hours, there was little olfactory show 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 upwardly on this equally it develops. For more than on this topic, please see our reporting on how to clean wildfire fume from your home.