5 Tips for Buying a Furnace Filter

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Air filters on store shelves

Air filters are critical to HVAC system performance and the quality of your indoor environment. Whether you're simply replacing your old filter or purchasing one for a newly installed HVAC system, these tips will help you find the right filter for your needs.

1. Size matters

The size of the filter is typically listed in inches — 16" x 25" or 20" x 25" are common sizes. Correct sizing is important. A wrong-sized filter may not fit snuggly or provide adequate filtration. Check the furnace owner's manual or the furnace cabinet door for the size you need.

2. Consider thickness

Filters range in thickness from one to six inches. Generally, the thicker a filter is, the better filtration you'll get as the air spends more time passing through it. Check your system's specifications for the thickness you need. To alter your system to accommodate a thicker filter, you should contact a qualified HVAC professional.

3. Permanent or disposable?

Permanent and disposable filters are available. Permanent filters are more expensive to purchase, but they last a long time — typically five to 10 years. Permanent filters must be cleaned regularly to ensure performance. Disposable filters are cheaper, but must be replaced regularly according to manufacturer's instructions. Disposable units are more convenient, but the replacement costs can add up over time.

4. Get the right rating

Filter performance is measured by Minimum Efficiency Reporting Value, or MERV ratings, which range from 1 to 20. The higher the number the finer the filtration. For a typical home, filters rated between 8 and 13 are adequate for removing most dust particles and other contaminants.

5. Choose your type

You have a variety of options when it comes to choosing the type of filter you want.

  • Fiberglass filters are cheap and allow maximum airflow, but are less effective at eliminating tiny contaminants.
  • Pleated filters are designed with pleats that aid in filtration. Pleated filters are more expensive than fiberglass models, but they are more effective at cleaning the air.
  • Electrostatic filters can be washable or disposable. They use self-charging fibers to attract particles out of the air. Dirt is trapped deeper into the filter, but electrostatic models are more expensive and may reduce airflow.
  • High-efficiency particulate air (HEPA) filters provide a high level filtration for those with severe allergies or respiratory conditions, but they can restrict airflow and reduce efficiency in air conditioning and furnace systems. HEPA filters are restricted for use in standalone air purifiers.

The type of filter you choose could depend on your budget, HVAC system and your indoor air quality needs.