ALL ABOUT MERV RATINGS
WHAT IS A MERV RATING?
A national organization established in 1894, ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) developed the standard for testing air filters for efficiency. The results of the tests are expressed in MERV (minimum efficiency reporting value). Simply stated, the higher the MERV number, the more efficient the filter will be in removing contaminants and pollutants from the airflow.
HOW MANY MERV RATINGS ARE THERE?
There are 20 MERV RATINGS, MERV 1 to MERV 20, MERV 1 indicating the lowest efficiency air filter. Most residential applications use MERV 6 to MERV 13. Filters with MERV ratings higher than MERV 13 are used in hospitals, clean rooms, commercial airplanes, and industrial and medical applications.
WHICH MERV RATING FILTER IS BEST FOR MY HOME?
MERV ratings are arrived at by tests that measure a filter's efficacy in capturing particulate matter which includes harmful indoor pollutants and contaminants. The higher the MERV rating number the better the air filter is in cleaning the air in your home. However, filters with MERV ratings from 14 to 20 are not recommended for residential systems because they pose too much resistance to air flow. It's safe to say that hundreds of millions of MERV 13 filters have been used in residential (homes) and light commercial applications with no problems.
IS A MERV 13 FILTER BETTER THAN A MERV 8 OR MERV 11?
Yes, a MERV 13 captures more particles which include harmful indoor contaminants and pollutants than a filter with a lower MERV number. The downside of getting a MERV 13 as compared with MERV 11 or MERV 8 is that the MERV 13 costs more and poses more resistance to the air flow. However, be mindful that MERV 13 air filters have been engineered by HVAC (Heating, Ventilating, Air Conditioning) engineers to work in residential systems without posing too much resistance. In fact, hundreds of millions of MERV 13 filters have been installed in residential systems for about 20 years with no problems.
DOES A MERV 13 FILTER HAVE TOO MUCH RESISTANCE?
There have been hundreds of millions of MERV 13 filters installed in residential furnaces and air handlers all over America without any problems. All air filters start out with relatively low air flow resistance. As the filter loads with particles the resistance increases. Believe it or not, as the filter gets dirtier it becomes better at capturing particulate matter. However, at the same time air flow resistance increases. As the filter continues to load more and more the filter reaches a point where the air flow is so restricted that it will start to negatively affect the system performance and may even damage the air conditioning system. Of course, the way to avoid this problem is to replace the filter regularly.
HOW OFTEN SHOULD THE FILTER BE CHANGED?
Deep pleat filters, 4 and 5 inch deep air filters lasts much longer than 1 inch filters. A rule of thumb is to change the deep pleat filters every six months, but the truth of the matter is that when to change a filter can depend on a number of factors. For instance, how often does the system run? Does it run more in the winter or does it run more in the summer? Another thing that affects the loading of the filter is how dusty the neighborhood is or if there is construction taking place in the neighborhood. Some homes have a dirt road in front of the house that raise a lot of dust when cars drive by. While the 6 months rule of thumb is generally a good rule to follow, those things mentioned above should be taken into account in deciding when to check the filter. There are filter gages that can indicate when the filter should be changed but these gages can be overly sensitive and hard to install for some people. So, when all is said and done the most practical way to know when to change your filter is to simply look at it. If you look at it after three months and it looks totally clogged, well then, it goes without saying, it's time to change your filter.