What Is Fpr Rating On Air Filters

As much as I've written about filters and filtration in this blog, I accept to confess there'due south one aspect of filter efficiency I've resisted learning about. Every article I've written that mentions filter efficiency talks virtually simply one rating calibration: Minimum Efficiency Reporting Value (MERV). A couple of other scales are in mutual employ, likewise, but I only didn't want to know anything well-nigh them because I purchase and recommend MERV rated filters. Only I took the plunge recently, and here's what yous ought to know about the three main filter rating systems.

Minimum Efficiency Reporting Value – MERV

The standard rating arrangement for filters is called Minimum Efficiency Reporting Value, or MERV. When I say information technology'southward the "standard" rating system, I mean it. This rating arrangement is defined in an ASHRAE standard (52.2), which specifies the performance required to meet each MERV level and the testing required. Higher-MERV filters remove more than particles from your air. They also remove smaller particles. A standard fiberglass one-inch filter is typically a MERV two. The high finish of the calibration is MERV-16. (It used to be 20, merely ASHRAE dropped information technology to 16 years ago.)

Before nosotros go further, we need to define the iii general size ranges of particulate matter (PM).

Range 1: 3.0 to 10.0 microns (includes PM10)
Range 2: 1.0 to 3.0 microns (includes PM2.5)
Range 3: 0.iii to one.0 micron

The words making up the MERV acronym are a bit unwieldy – What did y'all expect from engineers? – but the "minimum efficiency" part is the most of import. For a filter to get the MERV-13 rating, for instance, information technology must filter out a minimum of 90% of the Range one particles (PM10), a minimum of 85% of the Range ii particles (PM2.5), and a minimum of l% of the Range 3 particles. Beneath is a chart from John Semmelhack showing the percentage of particles removed by size range of particle and the MERV rating of the filter.

As you can see, you've got to stride upwardly your filter game to at least MERV-x to get even half of the PM2.v. Only you actually should think of MERV-thirteen as the minimum because it removes more than 85% of those item lilliputian bitty invisible pieces of stuff. For the COVID-xix pandemic of 2020, ASHRAE has started recommending at least MERV-fourteen.

Filter Performance Rating – FPR

The Home Depot sells a lot of filters. Rather than use MERV ratings, though, they decided to create their own rating arrangement. The details of their testing are a flake murky, as their website explains it in wide strokes only. They await at how well a filter catches both large and pocket-size particles and rank the filters on a 1 to ten scale. From that, they reduce the scale to four numbers (four, vii, 9, or 10), based on a weighted average calculated according to these percentages:

Sixty percentage of the rating is determined by the filter's ability to capture big particles, thirty pct is determined by its ability to capture small particles and weight proceeds over the filter's lifetime determines the final ten percent.

Here are the four FPR ratings you'll find on filters at Home Depot:

four Good
7 Better
ix All-time
x Premium

They must be using a different definition for the word "all-time" than the one I'm familiar with because their premium is amend than best. If yous're wondering how FPR compares to MERV, the Dwelling Depot website has a department on that. They outset by saying, "FPR 10 is similar in strength to MERV twenty, since they are both the highest rating value." They're a bit out of appointment, all the same, because the MERV rating goes up to a maximum of 16 now, not 20. Some filters on their website have both an FPR and a MERV rating, and at least one with an FPR of 10 is shown as equivalent to either MERV-8 or MERV-13. (See screenshot below.) Conspicuously, this isn't clear. Is an FPR-10 the aforementioned every bit MERV-16 or MERV-13 or MERV-8?

They don't provide easily available information on the sizes of what they call large and small-scale particles, and then information technology'due south hard to know what you're getting with a particular FPR rating. When you combine that with the difficulty of comparing FPR to MERV, it seems the best yous tin do with this scale is to utilise it every bit a rough guide. And if you want to filter out as much of the PM2.v as yous tin, stick with the FPR-x or find one with that also has a MERV rating and become with MERV-16.

Microparticle Operation Rating – MPR

As with Dwelling Depot's Filtration Performance Rating, the Microparticle Performance Rating was developed by a company with a financial involvement in the auction of filters. In this case, it'south 3M, the maker of the Filtrete line of filters. Different the FPR, though, the MPR measures the effectiveness of a filter'south capturing simply the smallest particles on the MERV scale: 0.3 to ane.0 microns. Their website says, "Your filter'southward MPR (Microparticle Performance Rating) indicates its ability to capture tiny particles between 0.iii and 1 micron in size."

Chances are good, though, that if a filter captures a lot of the minor particles, it volition capture even more of the larger particles. The scale just won't tell you anything about how well it does with particles larger than 1.0 micron. And nosotros should annotation that two.5 microns, the upper limit of PM2.5, is in the group of larger particles not covered by MPR. Patently they practise measure the larger particles, however, because they have a folio comparing MPR to MERV, and at that place y'all tin download a table of capture efficiency data showing the three ranges of particle sizes used in the MERV scale.

The MPR organization, like the other ii, uses a numerical calibration on which higher numbers signal better filtration. The MPR scale, all the same, uses much larger numbers. Their basic filter is rated at 100 and their most efficient filter is rated at 2800. The MPR-2800 would qualify equally a MERV-fourteen, so even though 3M emphasizes the smallest size range of particles, their best filter doesn't authorize for the highest MERV rating.

My recommendation is to buy filters with a MERV rating whenever possible. All 3 ratings have their bug just even Home Depot and 3M admit on their websites that MERV is the industry standard for rating filters. Also, if you desire the filter to improve your indoor air quality and not but protect the heating and air-conditioning system, go with MERV-13, FPR-10, MPR-1900, or higher. But make sure you can do that without reducing air menses and mayhap damaging your arrangement.

Allison Bailes of Atlanta, Georgia, is a speaker, writer, building science consultant, and founder of Energy Vanguard. He is likewise the author of the Free energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.

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