Two air filters sitting on top of one another

Everything You Need to Know About the Air Filter

Your HVAC’s air filter isn’t very complicated but it plays a crucial role in the performance of your heating and cooling equipment and your indoor air quality. Here, we answer our customers’ most frequently asked questions so that you can take better care of your central air system.

Air Filter FAQ

Why Do I Need to Change the Filter?

The average household generates about 40 pounds of dust annually. Your HVAC’s air filter is your first line of defense against all those particles. It traps dust, pollen and other airborne pollutants in a bed of tightly woven fabric, protecting your heating and cooling components and improving your indoor air quality.

Over time, the filter will become clogged. A clogged filter suffocates airflow, compromising your comfort and spiking your energy bills.

What Size Filter Do I Need?

If the filter’s dimensions aren’t displayed on the cardboard surround, you’ll need to measure the air filter.

  • Before you remove the filter, turn off the HVAC unit at the thermostat.
  • Pull out the air filter. It’s usually located in a slot on the bottom of the air handler. Some air filters, however, can be found in the air return register vent, typically located on the ceiling or hallway wall.
  • Begin by measuring the length. If your filter isn’t a square, the length is the shortest measurement. Then measure the width and the depth (the filter's thickness.)
  • You’ll likely end up with measurements in fractions of an inch. Example: 11 ½ x 19 ½ x ¾. Filters usually aren’t sold by their actual dimensions, so you’ll need to round up every fraction to the nearest whole number. Example: 12x20x1. This is called nominal size.

What’s the MERV rating?

MERV stands for minimum efficiency reporting value and it indicates how effective a filter is at trapping small contaminates. The MERV scale ranges from 1 to 20. The smaller the pollutants, the higher the MERV. Filters with a MERV of 7 to 13 are sufficient for most households. People with allergies and other respiratory sensitivities should consider filters with a MERV in the 11 to 13 range, as these can trap dust mites, mold and bacteria.

Filters with a 16-20 MERV are designed for sterile environments, such as health care facilities.

How Often Do I Need to Change the Filter?

Manufacturers recommend changing the filter every 30 to 90 days, but the frequency of replacement depends on several factors:

  • Filters with a low MERV rating will need to be changed out more often than high-efficiency filters.
  • Filters will require more frequent changes during periods of high HVAC use. You can expect to replace the filter at least every 60 days during the summer and every 90 days during spring and winter.
  • Households with pets will likely require more frequent changes. Pet hair and dander will clog a filter at a faster rate.

How Can I Tell If My Filter Needs to Be Changed?

A quick visual inspection should tell you enough about the filter’s condition. If it’s noticeably gray and dusty, it’s likely due for replacement. Watch for these other red flags that it’s time to change out the filter:

  • Dusty air vents
  • High energy bills
  • Weak airflow

Bottom line: Replacing your filter will help improve your indoor air quality. But if you’ve been diligent about regularly changing it out and you’re still dealing with excessive dust, you may need an advanced IAQ solution, such as duct cleaning. Turn to the Gainesville indoor air quality experts at Mid-Florida Heating & Air by calling (352) 310-0022.

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