We hate to be the ones to break it to you, but those expensive brand-name filters you’ve been buying lately might not actually be doing as much good for your indoor air quality as you’d hope. In fact, they may very well be damaging your central heating and air conditioning system and, in-turn, driving up your utility bills.
Amongst industry professionals alike, there lies much mystification when it comes to central AC system airflow, air filtration and indoor air quality. Airflow is, hands down, the most important factor affecting the performance and efficiency of your central AC system and the air filter you select can have a significant impact upon it. If you select a filter that sifts the smallest, finest particles, your AC and heating system’s airflow could become restricted, resulting in unsatisfactory performance and efficiency.
So what is the best way to proceed?
Unfortunately, there is no simple solution for many homeowners. However, here are some things to consider:
The air filter on your central AC serves two functions:
- To protect your equipment from becoming laden with dirt, dust and debris
- To remove dirt and contaminants in the air stream in order to improve the quality of the air we breathe
Improved air quality via filtration is not an attainable goal for many homeowners, as most central air conditioning systems can accommodate only a one-inch thick air filter – which [by physical definition] has limited surface area. Four- or five-inch thick media filters – with an accordion effect – encompass an additional twenty or more square feet in surface area than of one-inch thick filters composed of the same material. The greater the surface area available through which the air can pass, the more air molecules can pass through – Also, the less often you will need to replace it. As a result, when you use tightly woven materials in a one-inch filter – in order to filter smaller particles – the filter rapidly becomes too restrictive. Add some dirt to the filter, once it has been in place for some time, and it becomes even more restrictive to airflow and can literally choke off the air to your AC system.
So, what should you do?
If your AC system only accepts a one-inch thick filter, using an inexpensive MERV-5 or -6 fiberglass or pleated filters and changing them frequently is your best bet. These filters will not help much with indoor air quality, but should help to protect your equipment. MERV (Minimum Efficiency Reporting Value) is a filter effectiveness rating scale. A MERV-5 or -6 filter is about twenty-five percent effective at removing larger particles such as mold spores and larger dust particles.
If your AC system is or can be equipped with a thicker media filter, you are in better shape and have more filtration options. Because a media filter has far more surface area than a one-inch filter, you could use a MERV 11 filter, which is about eighty-five percent effective with mold spores and larger dust particles. A media filter can both protect your equipment and improve your indoor air quality without degrading your AC system’s performance and efficiency.
A four-inch or wider MERV 11 media filter offers the most cost-effective air filtration for homeowners. In fact, the City of Austin Green Builder program recommends that a 4- inch media filter be installed in all new homes built in Austin.