Furnace Filter Efficiency: Factors To Evaluate

by Greg Leisgang on October 6, 2011

Posted in: Furnaces

To properly evaluate the efficiency of your furnace filter, you need to understand the factors that influence how filters are rated and what the ratings mean.

Defining Furnace Filter Terms

There are a few vocabulary terms to understand as you begin evaluating furnace filter efficiency:

  • Efficiency refers to the filter’s ability to keep bacteria, mold, dust, and other small particles from passing through it. The initial efficiency of a filter when it is new will not be the same as its sustained efficiency over time.
  • Pressure drop refers to the filter's ability to allow air to flow through it. Denser material restricts airflow and increases pressure, which makes your furnace work harder, while lower pressure allows more air through and helps the furnace to run at peak efficiency. In general, as a filter collects particles, its airflow decreases.
  • The dust holding capacity of a filter shows how much dust it can hold at a specific pressure drop.

Rating Efficiency 

The Minimum Efficiency Reporting Value (MERV) rating system makes it simple to compare the efficiency of different filters, even among different brands. This rating will tell you how efficient the filter is at trapping particles of various sizes, ranging from 0.3 to 10 micrometers. And MERV ratings range from 1 to 16, with 16 being the highest efficiency.  

To give you an idea of how these ratings apply, it is helpful to considers some examples:

  •  A standard disposable filter usually has a MERV rating of between 1 and 4.  
  • A filter with a rating between 5 and 13 is in the middle range and is usually a pleated filter.
  • Filters with a rating between 13 and 16 remove the smallest particles, and are most often used in hospital settings.
  • High Efficiency Particulate Air (HEPA) filters are generally rated between 17 and 20, and are high-quality filters; however, their dense surface material greatly restricts airflow. Consult a professional to explore how you can safely use a HEPA filter in your home.

When choosing a filter, it is best to get help from the experts. Contact JonLe Heating and Cooling today to find out more about what filter will work best for your needs. 

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