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Complete Guide to Merv Ratings

Master The MERV: Air Filter Ratings, Explained

Choosing to install air filters to protect your space is a no-brainer. Air filters are an essential part of any business office, household, and apartment. Read this to understand the basics of air filters and why they are needed. When picking out your air filters, the classifications might get confusing. The acronym MERV sounds like a graduate school exam, and the numbers might as well be gibberish. It may be tempting to pick the highest-numbered MERV and run with it. Just because it is the highest, does not mean it is the best. Many consumers would be better off buying a MERV 8 or 11 over a MERV 15. Below, it will all be explained. Through understanding the many different filter classifications, learning which MERV levels are ideal for each specific situation, you will truly master the MERV, and become the foremost expert on which air filter is the best for you.

Established in 1987 by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), MERV stands for the Minimum Efficiency Reporting Value, and is used by the National Air Filtration Association (NAFA) to classify air filters by efficiency, particle size ranges, and ranges of applications. The way the classification system works is through numbers, or more accurately, levels. Each MERV level helps quantify each type of filter’s effectiveness relative to other filters. Each increasing level indicates a higher level of effectiveness across the standards mentioned above (efficiency, particle size ranges, and ranges of applications.) There are sixteen different MERV levels, and those sixteen levels are divided into four tiers. Each tier has its specific designations in terms of effectiveness and uses.

Higher MERV levels mean higher quality filters. Corresponding with the tiers, MERVs 1-4 are classified as the minimum, offering the least protection and filtration for your HVAC systems. MERVs 5-8 are effectively able to cover residential and commercial spaces, offering an average amount of filtration. MERVs 9-12 are classified as superior. They do the job quite well, offering exceptional protection for their spaces. Finally, MERVs 13-16 are the best, the top of the tier, the ones offering maximum filtration and purification, the cleanest choice for the HVAC systems. Below, we will delve into each tier, explaining its effectiveness on a practical level, moving to its cost, and then finally, the typical uses for each tier of MERV levels, to help you understand the MERV system as a whole, and learn how to pick out the filter that is best for you.

TIER ONE: MERV Levels 1-4

MERV levels 1-4 are the least effective air filters out of the group. They only capture particles that are ten micrometers or greater in size, and they do not capture particles smaller than that, more colloquially known as “coarse particles.” This is a problem because according to the EPA, it’s those particles that can get into the lungs and bloodstream, making them especially dangerous upon inhalation. For all intents and purposes, they should be considered the minimum protection.

Once inhaled, these particles can affect the lungs and heart and cause serious health effects in individuals at greatest risk, such as people with heart or lung disease, people with diabetes, older adults and children (up to 18 years of age).

With all that being said, this tier is by far the cheapest tier. For reference, on Home Depot’s e-commerce site, a four-pack of MERV 1 filters (Size 20x20x1) costs the same price as one MERV 8 filter. And the MERV 8 filter is pennies compared to the MERV 13 filter, which is four times as expensive. While yes, they do not provide as much protection as the other, more high quality filters, this lowest tier has its important uses, especially for those looking to buy a large amount of filters, or those who are having financial trouble.

Typical examples of utilizations for tier one MERV levels are residential in nature, ‘window filters’ being the standout example. When the air conditioner is connected through the window, one of these filters may be a cheap yet serviceable way to ensure that the air you are breathing is just a little bit cleaner.

TIER TWO: MERV Levels 5-8

MERV levels 5-8 are on the low-end of the middle of filtration effectiveness, as suggested by their numbers. They are more effective than their low tiered counterparts, being able to capture particles between 3 and 10 micrometers wide, which covers most of the ‘coarse particles’ range outlined by the EPA. However, these MERV levels are not effective enough to capture the ‘fine particles’ which are under 2.5 micrometers wide, though according to the EPA themselves, the actual health and mortality effects of the fine particles are unknown and inconclusive.

Fine and coarse particles differ by their sources, composition, dosimetry (deposition and retention in the respiratory system), and health effects as observed in scientific studies. Though it is often hypothesized that specific components or sources may be responsible for particle pollution-related mortality and morbidity, the available evidence is not sufficient to allow differentiation of those components or sources that are more closely related to specific health outcomes.

In terms of cost, MERV levels 5-8 are generally on the cheaper side compared to their more expensive superiors. A rule of thumb for air filter MERV levels is: The higher the number, the higher the effectiveness; and the higher the price for the filters. As mentioned before, the MERV level 8 is comparable to four MERV level ones in terms of pricing, sitting at around $5 off a typical Home Depot E-Commerce search.

Yet when you are buying filters, whether for work or otherwise, you are never going to buy just one, which is why Custom Filters Direct has a system that allows you to buy multiple filters at once, customizing the size of the order, and the filter sizes themselves, to meet your specific air filter needs. We can even automate the process to send them to you monthly. The reason why we do that is because you may forget to order a new air filter that month and then you would be breathing in bad air, putting your health at risk until you remember to place an order. They offer the MERV level 8, (and 11/13) which is a bargain compared to tier three MERV levels, and especially tier four, where the price really shoots up.

Air filters with MERV levels between 5 and 8 are usually the standard for industrial workplaces, as well as commercial and even paint booths, too. Though of course, they can be used for residential purposes for those looking for cleaner air than the tier one MERV levels can provide. The filters sitting at MERV levels 5-8  may be the most balanced filters of them all. A reasonable price combined with the standard protection makes for cleaner, safer air at a real bargain.

TIER THREE: MERV Levels 9-12

This is where things start to get stronger- and more costly, but we will get to that later. The filters of MERV levels 9-12 are the tier below the highest, and deserve the runner-up spot for the most effective filters. These MERV levels hit the fine particle range, easily clearing the coarse particle and large coarse particle hurdles with a (literally) microscopic 1.0-3.0 micrometer range. These filters mean business and they are strong, effective barriers to the contaminants that are looking to plague your breathing space. That is very useful, considering what the EPA says about those polluted particles that are trying to get in your home.

Population-based studies, small repeated-measure panel studies, and acute exposure studies in humans support the conclusion that inhalation of particle pollution induces small changes in blood pressure, oxygen saturation, endothelial function, systemic changes in acute phase reactants, coagulation factors, inflammatory mediators, and measures of oxidative stress.

Small changes may not sound like such a big deal, but they can lead to these symptoms:

Systemic blood pressure and endothelial function changes, acute coronary syndrome (including myocardial infarction and unstable angina), increased ventricular arrhythmias in people with implantable (or internal) cardiac defibrillators (ICDs), exacerbation of heart failure, ischemic stroke, and cardiovascular mortality are all well-established clinical cardiovascular health effects associated with acute exposure to fine particles.

MERV levels 9-12 are more costly than the ones before it, but less so than the ones after. (See rule of thumb in tier two) A MERV 12 filter on Home Depot’s website is around $19, which is more than triple the price of a MERV 8 filter in the tier below, yet also way cheaper than the tier above, where again, the most expensive and effective filters live.

Just because the tier three filters are not as effective as the tier fours, does not mean they are bad. Quite the opposite, in fact. The filters rated at MERV levels 9-12 actually cover all the bases necessary for pure and clean air, meaning they can be used almost anywhere to automatically kick the air quality up a few notches. Whether for residential purposes, industrial, commercial, or otherwise, these filters are all-around players that are not as expensive as the tier above, but provide roughly similar air quality, making them an invaluable asset to any indoor structure.

TIER FOUR: MERV Levels 13-16

This is the final, strongest, most effective, (and most expensive) tier of HVAC filters. Tier four MERV levels are able to, unlike every other filter tier on the MERV level scale, cover the latter range of fine particles that are less than a micrometer wide. The range of these filters is between 1.0 and 0.30 micrometers wide, and obviously they cover the larger particles of the lower tiers, these filters create by far the cleanest and contaminant-free air. As the EPA demonstrated through a study, higher quality air leads to lower mortality risks.

The Harvard Six Cities Study found statistically significant associations between chronic exposure to air pollution and mortality (Figure 7), specifically for fine particles and other pollutants strongly correlated with fine particles. Air pollution was also positively associated with cardiopulmonary disease deaths. A follow-up study (Laden et al., 2006) assessing risk of death after considerable improvement in air quality in these six cities showed that the risk of mortality diminished in proportion to the reduction in air pollution. As shown in Figure 8, the mortality rate ratio decreased in each city as air quality improved.

That trend (see link above for the graph) likely applies to indoor air and its contaminants, too. The less contamination i.e particles there are in the air, the safer it is. Therefore, these filters, MERV levels 13-16, provide the highest health benefits and the highest mortality risk reduction. They cover everything.

However, that all-around coverage comes at a cost. A steep cost, both in the cost of individual filters and the cost of replacement. Individually, a good MERV 13 filter cost around $30. That may not seem like much, but remember: Filters go on every vent in your HVAC system. In an industrial workplace, with many vents and openings into the room, that $30 cost just rose to exponentially higher numbers.

In addition to the cost of individual filters, the replacement costs must also be considered. At higher MERV levels, the filters catch and hold onto too many particles, and many problems arise because of that, chief among them being disrupting air pressure and flow. Many residential HVAC units are not able to handle restrictive air flow, which the higher MERV levels typically create as time goes on. It can burn out the fan motor.

The only solution to this is to replace the air filters more frequently, because the higher MERV levels trap debris and particles so quickly it chokes the unit with restricted air flow. All this results in, in the end, is more of those $30 filters over every single vent every single month. Suddenly, it will get a lot more expensive to maintain these filters.

Typically, these filters are used in areas where the air has to be pure for health reasons, like a laboratory or sterile area. MERV 16 filters, for example, are typically used in hospitals or areas of surgery. For residential purposes, they are more uncommon, though are still used, especially if the health of the occupant is at risk. Truthfully, many of the lower MERVs will do the job for cleaning the air at a fraction of the cost and replacement problems. Again, for the average person, the highest MERV levels may simply not be worth the cost.

That is it! That is all there is to know about the MERV levels! Now that you have mastered the MERV, your next step is to get the air filters you need. Picking one MERV rating out of the top three tiers, those being MERVs 8, 11, and 13, Custom Filters Direct simplifies the MERV choice down to the three most optimal filters, cost-wise and efficacy-wise. We also offer customization, allowing you to morph the size and quantity of your filters to suit your specific needs. As well, we have an automated delivery system, so when it comes time to replace your filters, they will be at your door. Order online today, ensuring that your air is the best it can be.