Filters rated MERV 7-12 are typically considered to be suitable for residential HVAC systems. The mid-MERV is twice as much and the high-MERV is three times as much. A MERV rating of between 6 and 13 generally meets the needs of most residences. MERV and Pressure Drop What Makes the Difference? The chart displays the static pressure drop curves for filters at four MERV ratings. Readers with specific questions should refer to the applicable standards or consult with an attorney. This is an industry standard rating system. Firstly, MERV ratings range between a 1 and 20 scale, which denotes the effectiveness and efficiency of filters to catch specific air-particle sizes. The higher the filtering efficiency rating (MERV rating), the higher the pressure drop. Install the test filter in the test duct and obtain clean air filter resistance or initial pressure drop. Secure .gov websites use HTTPS FPR 10 is the same as MERV Ratings 13; MPR vs. MERV Air Filter Ratings. 3. (1000-3000+ Sq Ft Homes), Thermostat Says Heat On But No Heat? "name": "What is filter pressure drop? But what is MERVrating, exactly? } MERV rating ranges between 10 and 12 are suitable for removing a broad range of particles. 3.0-10.0 greater than or equal to 95%, 0.30-1.0 greater than or equal to 95% [CDATA[ Filter Rating: MERV 8-10 | FPR 5| MPR 600.MERV 8 air flow & pressure drop Sold in Packs of 624x24x4 MERV 8 furnace A/C filters are made with electrostatically charged synthetic media. Just dont leave it out for more than a day, as we advise in our FAQ post, Can I Temporarily Run My Furnace Without a Filter. Airflow through the vents is lower: Is the new filter causing low airflow? Depending on the design [] Their cost is often moderate and are within many budgets. When a filter is in use, it traps and gathers particles, the more particles that are trapped the harder it is for air to pass through; when this occurs the filters pressure drop rises. Generally, filters with higher MERV ratings have less airflow. Get Started With a New Filtration Strategy. The Air Conditioning Contractors of America assumes that the pressure drop across a . It is 75% efficient on particles 0.3 -1.0 microns, 85% efficient on particles 1-3 microns and 95% efficient on particle larger than 3 microns. On the other hand, a merv 13 filter can sift all the particles that a. They also found that air flow in the high-MERV filters dropped by 7% and 11% in the two HVAC systems compared to the low-MERV filters. "@type": "Question", In fact, some MERV 8 and MERV 9 filters have similar or higher pressure drops than the MERV 13 filters. They remove the bulk of dust we see in homes and offices. NEC 310.16 Table: Copper And Aluminum Wire Ampacity Chart, NEC 310.12 Table: Wire Sizes For 100-400 Amp Services (83% Rule), kWh To Therms Calculator + Conversion Chart (1 kWh = 0.03412 Therms), MMBTU To Therms Calculator + Chart (1 MMBTU = 10 Therms), Therms To MMBTU Calculator + Chart (1 Therm = 1/10 MMBTU), AWG To Circular Mils Chart (For 4/0 AWG To 20 AWG). Tankless Water Heater Wire Size Calculator: What Gauge Wire (AWG)? The chart below shows the MERV ratings. The performance ratings given above are adapted from equivalent EU and MERV ratings and test classifications for filters as outlined in AS1324.1, EN779 and ASHRAE52. The M in MERV rating stands for Minimum. As you can see, the HEPA filters surpass the most restrictive 0.3-1.0 micron particle size interval MERV rating is based upon. "@type": "Question", Efficiency is measured by the percentage of particles captured. The COVID-19 pandemic has caused concerns about data center HVAC (heating, ventilation and air conditioning) filtration. Grainger Editorial Staff. Frankly, that can happen with about any filter higher than a MERV 5 if it gets dirty and clogged. These air filters are used to protect people or products from airborne contaminants. They will not hook up to your furnace or HVAC system. Just make the filter bigger and you get a lower pressure drop. Save my name, email, and website in this browser for the next time I comment. The pressure drop of a MERV 8 pleated air filter is around 0.12 inches of water, which is almost exactly the same as the 0.10 of the fiberglass. For reference, a typical dust particle is between .2 and 8 microns, while pollen starts at 7 microns and can get up to 70 microns in size. The more tightly woven or thick a filters media is, the more particles and contaminates the filter can trap. A .gov website belongs to an official government organization in the United States. The range is from 1 (lowest efficiency) to 20 (highest efficiency). 3.0-10.0 greater than or equal to 90%, 0.30-1.0 greater than or equal to 75% "mainEntity": [{ The MERV 5 is an excellent entry into the pleated filter lineup because it is low cost, readily available, and will . The majority of residential HVAC systems use a 1 thick filter, but filters are available at 2, 4 and 5 thick. Dust Mites. The poorest performance of the filter on all three particles sizes during each of the 6 cycles is used to determine the filters MERV rating. Low initial resistance and high dust holding capacity requires less energy consumption, resulting in lower operating costs and energy savings. Frequent filter changeoutsare necessary to reduce the possible negative effects a loaded filter can have on your HVAC equipment. This value is helpful in comparing the performance of different filters The air filter's efficiency has an indirect impact on airflow. As air moves through a buildings HVAC system, air filters trap and collect large and small particles such as dust, allergens and microorganisms. We recommendMERV 11 filtersas our better air filter. MERV Rating Chart Understanding MERV Ratings All filters have a MERV rating that falls between 1 and 16. For example, if bacteria ranges from 0.3 microns to 4 microns, the chart indicates a MERV 13 would be the minimum rating to select, and higher MERV-rated filters should be selected with the end users' level of comfort and Two 14X14 filter grilles are way too small. The good news is that institutions and other commercial/industrial facilities can take steps to lower their operating costs by adjusting their air filter strategy, namely by using higher quality filters to save money in the long run. "@type": "Question", Again, it has a pleated design. . Want to work for Air Filters Inc.? This rating system reports how well the filter captures and holds dust. "text": "As dirt and debris gets trapped by the filter, there is less space for air to pass through, causing the pressure drop to rise throughout the filters life. Because the pleated design creates more surface area, which is a less restrictive design. This chart shows their stated resistance to air flow in inches of water column (IWC/i.w.c.) Their average efficiency from 3 to 10 micron is less than 20. Simple use of MERV rating chart for air purifier filters: The higher the MERV rating, the better the filter. It ensures reliable and consistent testing of air filter performance. Welding fumes and milled flour are this size. About Us | Contact Us | Privacy Policy| Cookie Policy| Terms of Use| Do Not Sell My Info. ", They used a 20 x 20 filter. These values are shown to reflect the common vernacular used by many players in the filtration industry, Generally, the higher the MERV (M), you get better filter performance. I know that filter may look pretty dirty, but the light . "text": "An air filters pressure drop is the measurement of resistance to air that passes through the filter. build your custom filter now, Send us a message below or call us at 1.800.667.8563. This is your main concern. "acceptedAnswer": { The higher the MERV rating, the more a filter can capture and the cleaner the air will be. Pros. MERV rating. They are washable. 1994-2021, W.W. Grainger, Inc. All Rights Reserved. The filters initial pressure drop (initial resistance) will vary by the filter type, MERV rating, and size. Heres one example: We compared three filters of a popular brand and the same size (20x25x1) with MERV 5, MERV 11 and MERV 13 ratings. "@type": "Question", "@type": "Answer", The rating system is called ASHRAE Standard 52.2-2007. "name": "What are the signs of unhealthy static pressure in an HVAC system? Air conditioning air ducts air filter air filters air filtration air purifier air purifiers air quality airborne particles airfilters airflow asthma dust filter filters filtration filtration and disinfection filtrete flu heating and air conditioning hepa filter hepa filters history of merv indoor air quality made in the usa merv microparticle performance rating. "acceptedAnswer": { An air filter's minimum efficiency reporting value (MERV) rating measures how effectively the filter stops dust and other contaminants from passing through the filter and into the air stream. "@type": "Question", These filters capture particles at 10.0 microns in size, including pollen, dust mites, and carpet fibers. Camfil makes the best filters on the market: they are the most energy-efficient, have a longer and more effective service life than other filters, and feature a lower pressure drop than competing brands. How efficient the filter is against all three size ranges is compared against a MERV chart and the final MERV value is the highest value where the filter meets all three requirements of MERV. According to the standard's application guidelines, particles in this size range include pollen, dust mites, mold spores, hair spray, powdered milk, and of course, snuff. This value is used at the filters lowest efficiency. In other words: HEPA filters are better than anything MERV rating can measure. Always refer to your air handler manufacturers guide before changing your air filter. M values 1 through 4 are designed to remove large particles. Arrestanceis a measure of the ability of an air filtration device to dust from the air. (std. We will help you understand your best air filtration options. This will NEVER affect our opinion of a product or service! This also means that as the MERV rating goes up, the more particles and contaminants the filter can capture. With finer filtration, fewer airborne contaminates & dust particles are allowed to pass through the filter. For facility managers this has provided a variety of challenges, including considerations around increased pressure drop in HVAC systems due to the more restrictive nature of filters with higher MERV ratings. Likewise, the mid-MERV filters also showed decreased air flow relative to the low-MERV filters, this time 3% and 8% lower in the two systems. Filters with higher MERV ratings are more restrictive because they are capable of filtering more particles than filters with lower MERV ratings. It was about 0.08 inches of water column (20.7 Pascals). This often coincides with a higher MERV rating; however, this also means that the filter is slightly more restrictive and the airflow rate through the filter is lower. The "dirt" on the filters adds resistance. Ultimately a dirty filter will have the same impact on an HVAC system as using a filter with a MERV level that is too high for the equipment. They offer good airflow. Since MERV 13 filters (https://www.rpfedder.com/filtration/merv-13-filters/) are on the higher end of the rating scale, they can be susceptible to excessive pressure drop. What are 'Dark Factories,' and Do They Really Exist? They specify a minimum MERV of a filter to use, but not the IR. Pleats look like an accordion, and can more than double the face area of a filter. "acceptedAnswer": { The most prevalent MERV ratings are MERV 4, 6, 8, 10, 12, 14, and 16: A Higher MERV rating automatically means a better filter. air), Sensible Heat (BTU/hr) = 1.1 x CFM x t (std. 99.97% of particles in the 0.3-micron range. When your HVAC system is running the filter slows and limits the air that is being pulled through your vents and ducts. The manometer below shows my reading across one of the clean MERV-13 filters. Spun fiberglass almost always has a lower IR than other materials. "@type": "Answer", This guideline determines a filters performance by particle size. What Are All Those Gadgets On A Multitool? in the Inch-Pound system of measurement. LakeAir Products are really made in the USA. This system is designed by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). There is still a common misconception that having a high MERV rated filter will be too restrictive and strain your unit. "text": "The accepted pressure drop is different for each air conditioning or air handling system, and you should always refer to your manufacturers guide prior to inserting replacing your air filter to ensure you are using the appropriate filter. Building technology group ASHRAE has compiled recommendations for filtration, humidity set points, automation and more. MERV stands for Minimum Efficiency Reporting Value. What guidelines are available to compare air cleaners? The higher the MERV rating, the more particles the filter will remove. You can also reach us by phone at (585) 288-1600 or send an email to hello@rpfedder.com to get started. Here is Ron Wilkinsons (P.E.) MERV ratings 1 to 4 are generally only used as pre-filters but can be found in many typical applications like commercial buildings, furnaces, and window AC units. Many of our competitors claim read more. 99.97% or better for all particle sizes). We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. The accepted pressure drop is different for each air conditioning or air handling system, and you should always refer to your manufacturers guide prior to inserting replacing your air filter to ensure you are using the appropriate filter. Filters with higher MERV ratings trap small particles more effectively than filters with lower MERV ratings. We do not recommend M 12 or higher 13 filters. These filters are installed in two air handling units (AHUs) in the Delaware Biotechnology Institute. Take it out and run the system for a couple minutes. } Restrictive filters are one of many causes for low airflow, but if youve just installed a high-MERV filter and now air isnt flowing very well, this is likely the reason in this instance. Changing your air filters regularly will prevent filters from being loaded and overly restrictive. The E3 arrestance describes how well an air filter removes larger particles such as dirt, lint, hair, and dust. As the MERV rating increases the media typically becomes loftier and thicker, to capture more air pollutants, with this you could see slightly more air restriction." I normally see a product spec sheet with ASHRAE 52.2 testing, but I dont normally see Appendix J associated with it. MERV ratings are derived from the ASHRAE 52.2-2012 test which groups the particles sizes into three categories. Most current household HVAC units/handlers can handle a MERV 6-13 pleated filter with ease." A filter's MERVnumber indicates how it's rated to remove these particles. Rooms will be too hot or too cold: This is a symptom of low airflow. At the lower end of the efficiency spectrum a fiberglass or polyester panel filter may have a MERV of 4 or 5. depth MERV 13 filters are available with pressure drop characteristics comparable to or lower than some MERV 6 filters, staff also finds that a 2" filter depth is valuable in allowing filters to have airflow characteristics that are superior to a 1" filter, and may facilitate use of even higher MERV filters (such as the MERV 16 recommended by ", "acceptedAnswer": { PICKHVAC Terms of Use: Some of the products seen on our site are delivered through a relationship with outside suppliers like Networx.com, Google, and others. It isnt easy to navigate through 20 classes of MERV ratings. But before you update the filter, make sure it's specific. },{ ), CO2 Heat Pump Water Heaters Vs. Resistive Hot Water Heaters, MERV 13 Filter Pressure Drop: Guidance for Facility Managers, Free Tool to Measure the Air Changes Per Hour of Your Space, Mitigating the Impact of COVID-19 on Small Businesses By Improving Indoor Air, The In-Depth Guide to HEPA Filters in Hospitals, Medical Offices, & Clinics, Reopen Safely and In Compliance with NYS Mandates, Measure Your Spaces Air Changes Per Hour, https://www.rpfedder.com/filtration/merv-13-filters/. The scale rates how well a filter removes fine particulates from the incoming air. For instance, the most common cause of pressure drop is a dirty filter and some low-quality MERV 13 filters will clog more frequently, leading to increased pressure drop which requires more frequent filter replacements. Inexpensive and energy-efficient. Includes a moisture resistant, high wet-strength beverage board frame. Higher pressure drop = less airflow . It is an acronym for "high efficiency particulate air [filter]" (as officially defined by the U.S. Dept. "text": "Filters use various types of medias depending on the application or what the environment requires. The higher the MERV, the smaller the particles removed, and the more of them removed. "acceptedAnswer": { The amount of the HVACs air flow slowed by the filter is equivalent to the filters pressure drop. When selecting the right filter for your application, higher is not always better. "acceptedAnswer": { According to this paper, there's a well established connection between higher concentrations of particles in outdoor air and poor health outcomes, so it would make sense that filtering these particles out of indoor air could lead to better health outcomes. For example, a household pleated filter that uses synthetic media will have a lower pressure drop than a micro-fiberglass media that is used in critical environments such as a hospitals and datacenters. A filters material type and efficiency rating affect the pressure drop and resistance to air flow. It is quite an important filter-specific factor. Pressure drop directly corresponds to a filters air flow rate. However, one study found that actual pressure drops in home. They are not Minimum efficient. You can check the whole EPAs list of air pollutants here. The rating describes a filter's effectiveness at removing particles from the air. However, an important factor is that MERV ratings are not standard and the quality of a filter will vary from one brand to the next, meaning that pressure drop will vary between different filters that are rated the same. As you can see from the . These filters remove at least 99.97% of dust particle and are capable of removing viruses and radioactive material. These filters can cause restricted airflow. Many pleated HVAC air filters can still have a high MERV rating, while not drastically restricting air flow. Fiberglass and washable filters are typically 1-4 MERV, and can filter out particles of 10 microns and larger. The lower the pressure drop the easier it is for air to flow through the filter. Performance MERV 8 Air Filter MERV 11 Air Fir Filter Particle Size 3.0 - 10.0 microns 1.0 - 3.0 microns % Particles Captured 90% 95% Lasting Time 3 months 2 - 3 months Level of Usese Basic - Standard AFI Replacements (Air Bear, Honeywell, Trane), Poly Anti-Microbial Tackified 1 Inch Media 10oz, Poly Dry / Dry Tackified 2 Inch Media 15oz, Twist-Lock Cylindrical Cartridges for Pneuma Pulse, Flange-Top Cylindrical Cartridge for Farr Tenkay, Conical Cartridge for Donaldson GDX & GDS, Cylindrical Cartridge for Donaldson GDX & GDS, HEPA Crank-Lock Housing 2 Inch Pre-Filter, HEPA Crank-Lock Housing 4 Inch Pre-Filter, 2020 Air Filters, Inc. All rights reserved. LakeAir Commercial units have the ability to incorporate a MERV 14 High capacity media filter. MERV10, MERV 13, and MERV16) Pressure Drop Chart Static Pressures at variable CFM (in W.C.) Filter Number = 410 (MERV10), 413 (MERV 13), 416 (MERV16) CFM 400 = .03, .05, .07 CFM 800 = .07, .10, .13 When choosing a filter, remember that airflow (pressure drop) is just as important to consider as filtration (MERV rating). The higher the number, the better the filter is at capturing larger particles between 0.3 and 10 microns (m). Using the MERV rating chart to understand the filters and their applications. The wasted energy (and associated energy bill costs) required to push air through a higher MERV-rated filter to overcome the increased pressure drop shocks some owners. { This level of filtration does fall into the MERV system but they are shown here to add continuity to the overall filter picture. A 1 MERV 13 pleated filter has a pressure drop of around 0.27, and a 1 MERV 8 has a pressure drop of around 0.14. "acceptedAnswer": { They remove pet dander and most allergy causing air particles. In addition, poorly designed and installed duct systems already have external static pressures that are too high. The minimum efficiency reporting value, is a number from 1 to 16 that is relative to an air filter's efficiency based upon particle size. Typical Applications. Most current household HVAC units/handlers can handle a MERV 6-13 pleated filter with ease. Remembering to change your air filter is key to reducing the risk from pressure drop." 3M Pro Series Residential Air Cleaning Filters 4" and 5" filters last up to 6 to 12 months. They also found that airflow in the high MERV filters decreased by 7% and 11% in the two HVAC systems compared to the low MERV filters. Tankless Water Heater Breaker Size Calculator: What Size Breaker? Heres the definition of what that actually means: Definition: HEPA filter is a mechanical filter that must remove 99.97% (according to U.S. DOE) of particles whose average size is equal to 0.3 microns. The higher the MERV rating, the more efficient the air filter is at removing particles. It is measured in Pascals in the SI system. CFM Calculator Calculate Clean Air Flow. PickHVAC is also a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. The key is to look at the ratio of the filter area to the air flow rate. MERV17 through MERV20 filters are typically used in surgical operating rooms, clean rooms and other contexts that require absolute cleanliness. },{ Hathaspace Smart True HEPA Air Purifier Reviews, 4+6 Best Whole-House Dehumidifiers (Ducted, Portable), 4 Quietest Dehumidifiers (Best Bedroom Dehumidifiers): 52.1 dB Or Lower, 5 Best Air Purifiers For Cigarette Smoke In 2023 (+ Smell Removal), 5 Best Air Scrubbers For Any Kind Of Project (+Specs), 5 Best Coway Air Purifiers In 2023: Reviewed, Compared, Rated, 5 Medify Air Purifier Reviewed: MA-40 vs MA-25 vs MA-18 vs MA-15 vs MA-14, 8 Differences Between Air Purifiers vs Humidifiers (Head-To-Head Comparison), 1 Best Battery-Powered Air Conditioner: Shocking, Zeisty Truth, 5 Best-Of-The-Best Alen BreatheSmart Air Purifiers (2023 Review), BTU/h To Horsepower Calculator + BTU/h To HP Chart (To 72,000 BTU/h), Horsepower To BTU/Min: Convert HP To BTU Per Minute (Calc + Chart), HP To BTU/hr: Horsepower To BTU For A/C (Calculator + Chart). MERV 13 Pressure Drop Chart (Click to Zoom). The primary concern that some people have with the pressure drop issue is that of wondering if they are going to damage their HVAC system by using a filter with a high MERV. Since filters with a higher MERV can trap smaller particles, it is often assumed that they will automatically have a greater resistance to air flow. the expression of the Minimum Efficiency Reporting Value (MERV). Arrestance is a term often used in describing filter performance. This Standard is what led to the creation of the minimum efficiency reporting value, or MERV. air). From ASHRAE Journal Newsletter, December 8, 2020 . As an Amazon Associate we earn from qualifying purchases. In some ways they are better than all media filters in others they have drawbacks. Enter your info to get the catalog emailed to you! MERV means Minimum Efficiency Reporting Value (MERV) and is an industry standard that measures the overall effectiveness of air filters. Do I Really Need to be Concerned with the MERV/Pressure Drop Issue? We may or may not be compensated for purchased you make as a result of our recommendation. } At LakeAir, we recommendMERV 10 filtersas our good air filter. A numerical chart with values from one through 20 from 1 to 20 measures how effectively the filter stops dust and other contaminants from merv merv rated merv rating merv ratings merv stands minimum efficiency reporting value microparticle performance rating mpr minimum efficiency reporting value mpr mpr ratings range from 1 20 rated rating ratings signify an air filter's effectiveness at reducing airborne particles and contaminants standard 52 5 minimum the minimum efficiency reporting value. However, short of filter neglect, most modern HVAC systems are designed to be able to work with MERV filters in the range of 10 to 13. (Don't worry, we will have a full comparison chart at the end of this . MERV stands for Minimum Efficiency Reporting Value. The test is made of six cycles. However, if you are trying to filter out COVID-19 virus, they call for a MERV 13 or as high as your system can accommodate. Using an air filter with a MERV rating that is too high is as bad as using one that is too low. The amount of the HVACs air flow slowed by the filter is equivalent to the filters pressure drop. Air filters with MERV ratings of 7 to 14+ can have pressure drops anywhere from 0.05 to 0.3 inch WC, depending on filter thickness and air flow velocity. Weve identified that there is an increase in pressure drop and energy costs when switching to MERV 13 or higher filters. Thickness of the filter. Similarly, the medium MERV filters also showed a decrease in airflow . According to theAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE),this filtration helps provide healthier indoor air quality. The higher the filtering efficiency rating (MERV rating), the higher the pressure drop. How do I know if I need a higher MERV rating? It should be noted that pressure drop through a high-MERV filter varies depending on the velocity of the air flow. 2. These filters should not be used in home HVAC or furnace systems. Pressure drop is defined by the National Air Filtration Association (NAFA):The pressure drop of a filter is a measure of its resistance to airflow through it. The most prevalent MERV ratings are MERV 4, 6, 8, 10, 12, 14, and 16: MERV Rating In Air Purifier Specification Sheets (Or Lack There Of) A Higher MERV rating automatically means a better filter. The chart also provides instructions on how to determine electric fan energy consumed by AHUs in your own facility. Weve got em. A: Although ASHRAE does not recommend a specific MERV filter rating for preventing COVID-19 transmission, the organization suggests that upgrading systems in non-healthcare facilities to MERV-13 or the highest achievable level can be a worthwhile step in emergency response plans. Rather, they use simplified words that everybody knows. Need more details? Commercial Buildings. "name": "Does the material affect the pressure drop of the filter? A MERV 13 pleated air filter, the highest quality offering from Second Nature and most other filter companies, has a pressure drop of around 0.25. The performance is based on particles that are 0.3-10 micron in diameter. You can see from the MERV scale above that MERV 10 filter will filter out 85% of 3.0-10.0 m particles. Before we look at the MERV rating chart (1-20 rating for 0.3 10 micron particles), lets answer this question: Do you know why HEPA filters are called HEPA? The higher the MERV rating the better the filter is at trapping specific types of particles. Your HVAC equipment will give off a few clues that the filter is too restrictive and creating unacceptable pressure drop. Particles that are larger or smaller are trapped with even higher efficiency. The MERV rating is a measure of the ability of an air filter to remove particles from the air. How Much Does 500 Watts Cost Per Hour? "@type": "Question", },{ Contaminant Size Intervals. To get the right HVAC product and suitable MERV-rated air filter, you should know the area you want to use. This has resulted in confusion and apprehension on the part of the homeowner who wants to provide good quality indoor air, but not at the expense of that expensive HVAC system. What are they and why they matter? This value is helpful in comparing the performance of different filters, The rating is derived from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) [see. Depending on what size of particles the air filters can trap or let through, they are classified in a chart known as the MERV rating. Additionally, some brands drop their MERV rating almost immediately upon first use (e.g., a so-called MERV-13 becomes a MERV-9 as its used it cant hold its efficiency). ", P.S. There are no products matching the selection.
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