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Selecting & Replacing Furnace Filters

Everyone knows they are supposed to change their furnace filters. But, too many people don’t know the basic facts about furnace filters including when to change them and how to select a replacement filter. 

Changing Your Filters

So, the first question is, “how often should you change your furnace filters?” For maximum effectiveness, most furnace manufacturers recommend that you change your filters every three months. But, the life of a filter can vary depending on the conditions in your home and how frequently you use your furnace or air conditioning. You may need to change your filter more often if you have dirty ductwork, there’s construction going on in your neighborhood, you have pets or smokers in the house, or if you run the fan continuously.

A dirty filter causes your furnace to work much harder and will cost you more money in extra energy use and eventual furnace maintenance. Not to mention that the air quality in your home is suffering. At a minimum it’s recommend in San Diego we change our furnace filters twice a year: at the beginning of the cold season and again when summer starts to heat up.

Selecting the Right Filters

The next question is how to select a filter.  There are many options to choose from, including the older style spun fiberglass type to the more effective disposable pleated filters.

Air filters have a rating called MERV which indicates the filter’s ability to grab small particulates in the air. MERV stands for “Minimum Efficiency Reporting Value.” The higher the number, the greater ability of the filter to grab smaller particles from the air. The highest MERV rating is 20, which is usually reserved for scientific “clean rooms.”

The spun fiberglass will have a MERV rating of about 4 and do a pretty good job of grabbing larger particulate, but will need to be changed every 30 days. To capture the small particles in the air you should change to the pleated, electrostatically charged filters which will last 3 – 6 months. Ace Hardware brand basic filter has a MERV rating of 8. 

The Filtrete filters by 3M are more effective at reducing allergy-inducing micro-particulates with MERV ratings from 11 to 13. In addition to changing your filters regularly, you should have your furnace serviced by a professional at least once a year and have your air ducts professionally cleaned every 3 – 5 years.  

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