Columbus Ohio real estate

Who Is MERV and What Is He Doing Here


It's Furnace Friday... because every Friday is Furnace Friday on my blog.  Who's MERV? 

Last Friday was Furnace Filter Friday because it was the first Friday of October.  Did you change your furnace filter last Friday?  Or at least thing about it?  If you are changing your furnace filter monthly and missed last Friday... here is a second chance. 

If you are on a different schedule (not monthly) that is between you and your furnace.

I am Re-Blogging Jack's post about Furnace Filters today because I just can not resist it... I should save Jack's post  for Friday November 5, 2010 (the next Furnace Filter Friday on the calendar) but I can not resist.  

Great info about Who Merv is... Or MERV.  Thanks to Jack Gilleland a Dayton Ohio home inspector for allowing his furnace post to be Re-Blogged.


MERV is a number that is assigned to a furnace filter to help the consumer (and contractors) gauge what filter should be used for a specific environment.  MERV stands for Minimum Efficiency Reporting Value and someday hopefully it will be printed on all filters. Although now an international industry standard, the rating/value is not required on all packaging. Developed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to simplify the rating of filters, it is a minimum or worst case rating.  An example would be a low cost filter with a 1 rating would filter 20% of all particles of 3 to 10 microns in size.  For reference, a human hair is 20 to 40 microns in size. Now you may think that is pretty small, but it is only catching 20% of the particles in this range.  There is little change in the efficiency of the filter with a MERV rating from 1 to 4.  The rating system has ratings that run from 1 through 16.


Rating               Efficiency average particle size in microns.

    1-4               less than 20% effective on particles 3.0 to 10

    5-7               less than 49% effective on particles 3.0 to 10

    8-9               less than 84.9% effective on particles 3.0 to 10

    10-11            50 to 64% effective on particles 1.0 to 3.0

                        less than 85% effective on particles 3.0 to 10

    12-13               80 to 89% effective on particles 1.0 to 3.0

                        over 90% effective on particles 3.0 to 10

    14-15            75 to 84.9%  effective on particles .3 to 1.0

                        over 90% effective on particles 1.0 to 3.0

                        over 90% effective on particles 3.0 to 10

    16                over 75% effective on particles .3 to 1.0

                        over 90% effective on particles 1.0 to 3.0

                        over 90% effective on particles 3.0 to 10

(Sorry about the vague percentages on the chart once the ratings reach 14, but it is hard to pin down a bunch of engineers on anything.)

Engineers gauge the size of mold spores at an average of 3-12 microns and typical household dust at anywhere from .1 to 40 microns.  Local air quality professionals may be able to pin these down farther in your community.

All this data is pertinent for one reason.  Determine your need for the effectiveness of your air filter and buy the filter you need.  My personal opinion is that your wasting money buying any filter under a MERV rating of 8.  What do I use, a 10.

Jack Gilleland

Home Inspection Services, Clayton

Serving Dayton and the Surrounding Area


This post provided by Maureen McCabe HER Realtors*

Contact Maureen McCabe of HER Realtors* - 614.388.8249

HER Realtors  Maureen McCabe

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*Real Living HER

Information is deemed to be accurate but should be verified to your satisfaction.  Information provided herein is supplied by several sources and is subject to change without notice.  Opinions expressed are solely those of Maureen McCabe.



Comment balloon 2 commentsMaureen McCabe • October 08 2010 08:34AM
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