MERV Efficiency Rating for Filters

The common rating term for filters is MERV (Minimum Efficiency Reporting Value) as tested to ASHRAE Standard 52.2:

There are many filters out there claiming MERV 11 but i somehow doubt whether they really meet the MERV 11 claimed when i look at the chart in the above document!!!

I saw MERV 11 filters in a large box store the other day selling for $29 apiece. It would be interestingt to know what the Correct filters are rated at and what the customer is being charged???

Some other filter sites:

As you can see, you can get cases of a dozen MERV 11 filters for as low as $50…so why not sell them yourself. Or even better tell your customers about the on line deals…they’ll remember you and recommend you for helping them save many $$$$$$!!

Thanks Brian.

It is nice to have choices to offer our clients.

Coorectfiilters have aslo been tested by ASHRE, and have been assigned the MERV rating by ASHRE. The MERV rating for there plus product is 8 and the pleaated product is an 11. In adition to MERV ratings the Correctfilters have a patented ani-bypasss seal. In short all the air is filtered.

In addition there are several differneces: 1) the filters you show are made of paper and they will bend warp and break, Correctfilters are made from cast aluminum and so they fit perfectly and filter 100% of the air. Just becasue a filter has a high MERV rating doesn’t mean you it works well. 2) Correctfilters have an anti-mocrobial matter that is build in, these filters do not. Thus giving less protection against mold, bacteria and other matter 3) Correctflters calls the customer everytime it is time to change the filter. The number one problem with filters is human error. Correctfilters takes care of this issue 4) If you want to sell these filters you have to have them in stock or order them. This makes you repsonsible for all shipping and distribution. With correctfilters you never have to touch a product. In addition, you get paid for every year that the filters are bought.

There are lots of option avaiable for filters and there are several good products. What Correctfilters does, it makes the process easy for you and your customers. The customer never has to shop again for filters. Correctfilters are sent to their home, and you never have to do anything once the fikter is sold accept sit back and accept checks.
Correctfilters are sold for $120 for a one year supply and $99 for every year after. The inspector who sells the Correctfilters recieves 25% of teh sale price.

Only in a perfect world.

You must work for correct filters.

How many filters does one get for the $120 service?

From the NAFA Programs page:

NAFA Certified Products:
**Participating Companies
Aeolus Corporation
Filtration Group, Inc.

These products have been tested by a NAFA approved air filter testing laboratory using the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 52.2, 1999, to manufacturer’s listed values.
NAFA certifies that the product meets the manufacturer’s values.
*NAFA Product Certification provides a third party, random selection and testing for manufacturers and fabricators of air filter products. This certification is quality assurance for the end-user that the specifications of filter performance are correct as advertised. *
Full test results may be obtained from the manufacturer.

Where are the*** certified*** test figures from Correct Filters???

The truth be said you are not telling all the the facts . I personally spoke with you about the filters for your customers. You were upset because all of the filters did not get there at one time. This upset you because you assumed the filters would all be on one box and you went to the custmer home without one of the filters. This assumption was strange to me because you had already recieved multiple boxes, so it would be hioghly unlikely that all of the filters would come in one box.

Do to your inconvienece, I told you that we would ship another product to you and that it would arrive by the end of this week and it did. I also told you I would look into the filter that did not show. You said that was fine, and never asked us to ship a product to your customer directly or to make any other arrangements

Customer service begins with communication and obviously we failed at communicating together.

We regret that you feel like you had a bad experience with your customer and would be more than happy to refund your money.

Correctfilters stands behind its product and service. In this case it seems as thuough we both failed to communicate properly.

We hope that we can move forward and both agree to communicate more effectively. Please call me to get your refund.

Six filters for the initial price is actually not that bad. A couple bucks a piece each, more than the cheapest on the market…:cool:
It would appear that the filters ARE quite a bit better (purportedly) than standard filters off the shelf.

My experience observed in the field has been that people tend to NOT change the filters at all, until either an HVAC guy does it for them on a maintenance call, or an inspector makes a note of it in his report.

Given the automatic service of sending them new, clean filters, its my belief that this is a pretty good value service that I could participate in.

I’ll try to give it a whirl on the next inspection, if I get one soon…

Any chance there are brochures on this service, that I can just hand to the client?

That is a ****in lie. You told me that you were not responsible for shipping and that all three were shipped. You never said a word about shipping another one. The first person that said anything about shipping another was when Nick posted it on this board. Had you told me that you would ship another I would have asked that it be shipped directly to the client.

Why do you insist on digging the hole deeper for yourself. Everyone on this board knows that I will be the first one to admit if I make a mistake. Now everyone on this board knows that you will make up stories to protect your own *** instead of telling the truth and admitting that you made a mistake.

I will never deal with you or your company again. That also goes for Pro-Lab. I will be disputing the charge to correct filters and the charge to Pro lab for the materials that were delivered the same day that the two filters were.

Can you get some supporting independently verified evidence???


This Canada Mortgage and Housing Corporation (CMHC) article on furnace air filters was found in a newsletter out of Texas:

There is one thing to remember about going to higher merv filters. The airflow through the system may be severely reduced causing air conditioning to freeze or furnace to trip limit.

Good point to highlight, Gary.

The last 2 lines in the CMHC document are not as plain as to problems that may be caused but do mention airflow:

Make sure that your furnace technician approves a change to a high efficiency filter. Some of the filters with higher MERV ratings will reduce the amount of air passing through the furnace and affect its performance .

Comparative Tests on Pressure Drop of HVAC Filters
By Jim Rosenthal, 3/12/2008

We test 20 filters for pressure drop and efficiency.

It is often very difficult to compare pressure drop for HVAC air filters. Even though filter tests are standardized it is not unusual for the same type of filter to be tested in two different laboratories with two different results. In addition, filter tests are run at different speeds which has a significant effect on pressure drop numbers. In addition, marketing literature is not consistent and one can seldom compare published data from product to product. Consequently, there is a great deal of confusion in this area.
Furthermore, there are a number of myths in the HVAC industry regarding air filters. One of the most enduring is that “throwaway” one month filters are the only type of filter that can be used in some HVAC systems. The jist of the myth is that these filters are the only ones that have a low enough resistance to allow sufficient airflow for the system to operate adequately.
To build some good comparative data we tested 20 different air filters of various types, thicknesses and efficiencies. Our test duct is 8 feet long, two feet wide and two feet high. It holds 24"X24" filters with a depth of up to 20". The test duct fans can operate up to a speed of 750 fpm. A magnahelic gauge is installed that measures the pressure drop in “inches of water” from before the filter to after the filter.
Twenty filters were obtained for the tests. Ten were purchased at hardware and home improvement stores. The balance were various “commercial” filters from different manufacturers.
Each filter was tested at 300 fpm, 400 fpm and 500 fpm and the pressure drops were recorded. In addition, a laser particle counter that counts particles of 0.3 microns and larger was used to determine the ambient particle count and the particle count at the air exiting side of the test duct for each filter. The results of the tests are presented in the above table.

Filter Needs in the LEED Rating System

[size=2]for New Construction in the Green Building Catagory[/size]
[/size]By Jim Rosenthal, 9/8/2005
Building owners obtain points in LEED system with proper filtration.

The Leadership in Energy and Environmental Design (LEED) Green Building Rating System represents the U.S. Green Building Council’s effort to provide a national standard for what constitutes a “green building.” It is a design guideline and third-party certification tool that has become increasingly popular over the past several years as a way to improve occupant well-being, environmental and energy performance and economic returns. The LEED rating system covers all aspects of the design and construction of a building including air filtration.

The specific needs for air filtration are the following:

  1. A requirement is that the building meet ASHRAE 62.2 standards which means it must have at least MERV 6 filtration to be eligible.

  2. During construction if air handlers must be used, filtration media with a MERV 8 rating must be used at each return air grill.

  3. After construction MERV 13 filters should be installed and a two-week flush-out at 100% outside air should be conducted before occupancy.

  4. New MERV 13 filters should be installed prior to occupancy. Items 2, 3 and 4 in this list should be completed to receive points in the LEED rating system. There are various types of filters with a MERV 13 - everything from bags to mini-pleats. Each has different design requirements and pressure drop. We would suggest that building owners and designers consult with a Certified Air Filter Specialist (CAFS) to obtain the best information on the optimum filters and pre-filters to obtain LEEDS certification.

Hope this helps some.

Marcel :):smiley:


Interesting to note that the MERV 11 filter only reduces particle count by 11% at the 0.03 micron level. This is in the range of very small particles that we breathe deep down into the lungs. If true high efficiency filtration is needed, parallel-to-the-plenums HEPA filters should be used or individual room portable HEPA cabinet filters can be used.

The first thing to do though is follow the recommendations in the above mentioned CMHC article.

Can you get some supporting independently verified testing???

Mr. Tafeen:

You sent me a PM saying you would get some test results…we’re still waiting!!

Check Trane’s Clean Effects It was tested independently with the name of the testing agency listed. LMS Technologies.


We were asking about the Correct Filter 1" pleated media filters that were being pushed as almost the world’s answer to everything in the air!! I couldn’t find any info on their website.

The above unit appears to be an electronic (proper name: electrostatic precipitator) 6-8" thick filter. These have been around for years and always were quite efficient. Could be just the wording (over-embellishment) but they may have improved it a bit… They’re making claims about very low levels of ozone production.*

There’s very little to almost no technical data available on that Trane website!!!

Some other info:

AHA!! Some data from the Correct Filters’ website. Let’s analyse it!!! Plus Pad](

Product Specifications: Pad Type : CorrectFilters™ Plus (includes 1 year supply) Air Flow : .19 W.G. @ 300 FPM Dust Spot: 22.1% Filter Life: 60 Days Dust Holding: 22.9 grams Efficiency: 92.3% Arrestance INCLUDES: 6 CorrectFilters™ PLUS PADS…


]( Pleat Pad](

Product Specifications: Pad Type : CorrectFilters™ Pleat (includes 1 year supply) Air Flow : .18 W.G. @ 300 FPM Dust Spot: 35-40% Filter Life: 90 Days Dust Holding: 60 grams Efficiency: 95% Arrestance INCLUDES: 4 CorrectFilters™ PLEAT PADS…


My comments:

No independently tested MERV numbers and they don’t even show the third of the different accepted tests- the DOP- which is all about the smallest particles which travel deepest into the lungs. Why tell buyers the full story? They may buy someone else’s cheaper filter with better performance!!

Air Flow: [size=3]This is the pressure drop across the filter in inches water gauge when tested with air flowing at 300 feet per minute[/size]

[size=4][FONT=Comic Sans MS][size=4][FONT=Comic Sans MS][size=4]Dust Holding: [size=3]approx 28 grams = 1 ounce[/size][/size][/size][/FONT]

Efficiency (Dust Spot): [size=3]Of the 2 tests mentioned here, this is the one that tells the most. [/size]

Efficiency (Arrestance): [size=3]This is the test used in ads that, IMHO, is a scam used by the filter manufacturers!![/size]


Judging Filters and Air Cleaners

The results of standard tests can help you pick the right filter for your needs. Filter effectiveness is measured by two tests:
Arrestance tends to measure the filter’s ability to remove the largest, heaviest particles. It’s useful only for low-efficiency furnace filters. If you’re concerned about small particles, especially breathable ones, arrestance doesn’t give meaningful results.
Dust Spot Efficiency is a better way to measure removal of fine particles. Use it to compare pleated filters and electronic air cleaners.
Thermal DOP Efficiency applies to the very highest efficiency filters, such as HEPA filters. This is sometimes called “absolute” filtration.
Both arrestance and dust spot efficiency are defined in American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) Standard 52-89. Unfortunately, some manufacturers list filter “efficiency” or even “ASHRAE efficiency” in their literature, when they mean arrestance. Look for explicit mention of “dust spot efficiency.” Thermal DOP efficiency is tested according to U.S. Military Standard 282. It’s generally applied only to very high efficiency filters, such as the HEPA.
The filter industry divides filters into three groups by dust spot efficiency: Low-efficiency filters are less than 30 percent, with the typical furnace filter below 10 percent. Medium-efficiency are between 30 and 50 percent. High-efficiency are between 50 and 95 percent. “Absolute” filtration is a class by itself where dust spot efficiency is always above 95 percent.

Filter Efficiency

**Type…****Arrestance…Dust Spot…**DOP


Passive Elect…75-95%…<20%…–




The chart (above) illustrates how the effectiveness of different filters varies depending on particle size. Higher efficiency is usually better, but it can get complicated. Filters with 95 percent arrestance may catch almost all the lint, but few if any of the smaller particles. Many low- and medium-efficiency filters show their lowest efficiency between 0.1 and 0.5 microns. . Two filters perform well across the entire range of particle sizes: HEPA filters and electronic air cleaners.

Note: An analogy about the results of the ARRESTANCE test… It measures total weight of dust collected. If it were a seive for sand and pebbles, but most regular sized sand went through (like small dust particles) only a couple of stones will boost the weight of captured material and give a high percentage captured % (say 95%), making the filter look very efficient when it isn’t. Similarly, catching all the dust bunnies, lint, pet hair but letting most small dust particles go through the filter to be distributed throughout the house is what is happening with the arrestance test!!

For those who want more info: