MERV Efficiency Rating for Filters

[Brian A. MacNeish]

Originally Posted by mcyr

We test 20 filters for pressure drop and efficiency.

.
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.

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.


Hope this helps some.

Marcel

Marcel:

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.

[Brian A. MacNeish]

Originally Posted by Brian A. MacNeish

Bump!!

BUMP AGAIN!!
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!!

[Gary Reecher]

Originally Posted by Brian A. MacNeish

BUMP AGAIN!!
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 http://www.trane.com/Residential/pro...Air-Filtration It was tested independently with the name of the testing agency listed. LMS Technologies.

[Brian A. MacNeish]

Originally Posted by Gary Reecher

Check Trane's Clean Effects http://www.trane.com/Residential/pro...Air-Filtration It was tested independently with the name of the testing agency listed. LMS Technologies.

Gary:

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!!!
http://www.trane.com/Residential/Cle...fectsDemo.aspx

* http://www.consumerreports.org/cro/a...tor-advice.htm


Some other info:
http://www.consumeraffairs.com/news0..._purifier.html

[Brian A. MacNeish]

Originally Posted by Brian A. MacNeish

BUMP AGAIN!!
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!!

AHA!! Some data from the Correct Filters' website. Let's analyse it!!!

CorrectFilters 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…

$99.00
BuyMore
CorrectFilters 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…

$129.00


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: This is the pressure drop across the filter in inches water gauge when tested with air flowing at 300 feet per minute

Dust Holding: approx 28 grams = 1 ounce



Efficiency (Dust Spot): Of the 2 tests mentioned here, this is the one that tells the most.

Efficiency (Arrestance): This is the test used in ads that, IMHO, is a scam used by the filter manufacturers!!


From: http://oikos.com/esb/31/airfilters.html

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

Furnace..............75%.....................--......................--

Passive Elect......75-95%................<20%...................--

Pleated..............90-99%...............20-55%.................--

Electronic..............--....................90-95%.................--

HEPA....................--.......................--.....................99%

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:
http://www.arkansasashrae.org/Speake...%201206064.pdf

[Brian A. MacNeish]

Originally Posted by brian a. Macneish

bump again!!
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!!

bump again!!!

[Jason Yost]

It is a mistake for anyone to think that a filter in the HVAC system will reduce all of the particulate anyway. There are too many other sources of indoor air particulate than just the HVAC system. I'm sorry if I misunderstood someone on this post, but while these filters and that system is the best we have at this time, other considerations should be made when trying to improve the indoor air quality than just the filter size. I believe someone on here said that some systems can not handle a good filter because the pressure drops too much. That doesn't mean that there can't be corrections made to the system to make them work. Review of the system should be a standard consideration when making recommendations of filter type; also, system function - by that I mean is the air being distributed properly, diluted properly, and other maintenance kept up. I know most of you know this already, but after reading the posts something compelled me to place this on here. How often does the ventillation rates get checked during a home inspection? I only handle indoor environmental consulting, so I'm just curious. Does the system get checked for proper performance during a home inspection (duct placement, pressure, air flow, etc.)? Thank you.