Air Filters and your Heating and Cooling Equipment
By Chris Hall
Ever wonder why your air filters should be changed or how frequently? What do they really do?
Air filters serve an important role in the efficiency and proper function of your heating and cooling equipment. But what do they really do? A common misconception is they filter the air you breath in. They actually do something a little different and filter the air that enters the system, prior to being heated or cooled. They prevent dirt, dust, and other airborne particles from clogging the system. Clogged air filters are the number one cause of system failure.
Issues resulting from a clogged air filter
- Reduced air pressure. Clogged filters reduce the air pressure in the system, which will cause they system to run more often or for longer periods of time. This will increase energy costs and puts strain on the fan motor.
- Risk of overheating or freezing. When air isn’t circulated properly, your system can overheat or freeze (depending on the season). Your system requires constant air flow when operating to allow the equipment to function properly. Clogged filters reduce the air flow causing overheating or freezing.
- Mold and bacteria growth. When your filter collects airborne particles, mold or bacteria could form over time, given the proper conditions. This could lead to health issues for you and your family. Also, this could form colonies throughout the entire system, which can be quite difficult to mitigate.
4 Basic air filter types
- HEPA Air Filter
- Ionic Air Filter
- Activated Carbon Filter
- UV Light Air Filter
MERV Ratings for HVAC Filters
As you begin looking at filters, you may notice a MERV standard on many of them. The MERV (Minimum Efficiency Reporting Value) tells you how much dust and contaminants can pass through the filter. Filters with a higher MERV allow less particles through them. However, this is a double edged sword. Although less particles are passing through the filter, your HVAC system has to work harder to force air through the filter and into the house. Using a filter that has a higher MERV standard than is recommended by the manufacturer can be detrimental to a furnace and a home warranty company will be less likely to pay to repair and replace it.
The MERV rating was created by the American Society of Heating, Refrigerating and Air- Conditioning Engineers and the scale goes from 1 to 20. The rating is based on the size of particles that can get through the filter. ASHRAE tests filters for particles like pollen, dust, dust mites, and smoke when determining each filter’s MERV rating. A filter with a 4 on the MERV scale will filter out things like dust, pollen, moss, paint and fibers, while an 8 will filter out mold spores, dust mites and pet dander. The highest MERV (20) will filter out viruses, carbon dust, and smoke. (Usually, these are used for hospitals or clean rooms.) The United States Environmental Protection Agency says filters should be at least MERV 8 to meet indoor air quality specifications.
It is recommended that you replace the filter(s) every 30-60 days. It may need to be replaced sooner if you have pets or live in a high pollen area. They are generally inexpensive and very simple to replace. Some systems have only one filter, located at the air handler (commonly found in the basement/crawlspace, attic, or closet). Other systems have them in bedrooms or hallways. It all depends on the type of system designed for your particular home. Check the documentation or placard on your unit to determine the proper size and rating filter your need. When in doubt, research a reputable heating and air conditioning company to service your equipment.