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You are here: Air Conditioning and Heating > Filters

Filters

Air Filter Basics

Air Filtration is important to any home or building and basically performs two very important functions:

  • Keeping your air conditioning equipment clean and operating efficiently.
  • Cleaning the air that is circulated through your house or building and removing airborne particulate from the air that we breathe.
Regular maintenance and replacement of air filters is extremely important! Dirty filters can cause problems and create costly repairs:
filter
Picture of a clean evaporator coil next to a
dirty evaporator coil.
  • Low or reduced air flow
  • Higher utility costs
  • Reduced cooling and heating capacity
  • System freeze ups
  • Water damage
  • Compressor failure
  • Evaporator coil failure
It is important when selecting a filter type to consider all of the factors.  We recommend consulting your HVAC specialist before purchasing a filter. Factors to consider:
  • Initial cost
  • Required replacement or maintenance intervals
  • Efficiency and size of particulate removal
  • Resistance to air flow

Air filters come in all shapes and sizes and are composed of different materials.  Some filters are more efficient than others at removing particulate from the air stream.  Filter efficiency is measured for comparative purposes using the MERV Rating System.  Each filter is tested and given a MERV Rating.


What does MERV or MERV Rating mean?

Your filters MERV Rating is a good way to help judge the effectiveness of the filter. MERV means Minimum Efficiency Reporting Value which was developed by the American Society of Heating, Refrigeration and Air Conditioner Engineers - ASHRAE. MERV values vary from 1 to 16. The higher the MERV value, the more effective the filter will be in trapping airborne particles. Another consideration is air flow through your HVAC system. Leaving a dirty air filter in place or using a filter that is too restrictive may result in low air flow and possibly cause the system to malfunction.

ASHRAE recommends MERV 6 or higher
US Department of Energy recommends MERV 13
LEED recommends MERV 8 at a minimum.


Brief Description of Commonly Used Filter Types


Traditional Fiberglass or Polyester
Traditional Fiberglass or Polyester

These inexpensive, disposable, 1" or 2” thick filters are recommended to be changed monthly. Because their main purpose is to protect the heating and cooling system from damage, their media is dense enough only to capture large particles. This filter type is not very effective at capturing smaller, respirable particles from the air.

Washable/Reusable
Washable/Reusable

These 1" filters are designed to be washed out monthly and reused. This filter is typically an inexpensive filter and it can be used for a number of years before needing replacement. Tests show that this type of filter is not very effective at capturing smaller, respirable particles from the air. Although some brands of this filter type claim an electrostatic charge created by the air movement through the media, the charge is actually minimal and plays little or no role in particle capture. Some have a very high resistance to airflow which can adversely affect your system.

Ordinary Flat or Pleated
Ordinary Flat or Pleated

It is recommended that these disposable, 1"or 2” or filters be changed every 2 to 3 months. These filters are generally made out of cotton or polyester media which is denser than fiberglass and will typically capture more small particles than either fiberglass or washable/reusable. The filters can be found with either a pleated or flat media. Pleated filters create a wider surface area and allow for the use of a denser surface area without restricting air flow.

Deep Pleated
Deep Pleated

The previous 3 types of air filters are 1"-2” deep and can be used interchangeably. Deep pleated filters are 4” to 6" deep and thus can only be used on heating and cooling systems that are specially adapted to accept them. This filter type may have a reusable frame with replaceable media or constructed in a replaceable cartridge design. The deep pleated design allows this type of filter to capture smaller particles without adversely reducing air flow through the system. In addition the large surface area allows more particles to be removed over a longer period of time. Recommended replacement intervals for this type of filter is 6 to 12 months making it a good value with low maintenance requirements.

Electronic Air Cleaner

 

Electronic Air Cleaner

This type of air filter is a permanent fixture in the heating and cooling system and requires an electrical connection. Although it is significantly more expensive than any other type of air filter, it is very effective at removing particles from the air. However, it must be disassembled and cleaned regularly to keep its high level of effectiveness. Monthly cleaning is recommended making it a higher maintenance system. If this type of system is not maintained it can cause damage to your a/c and heating system. Also, these air cleaners may emit ozone, which can be harmful at high levels. It can also be costly to have repaired if it breaks down.

HEPA Filtration
HEPA Filtration

HEPA is an acronym which stands for High Efficiency Particulate Air. HEPA filters provide a very high level of filtration efficiency for the smallest as well as the largest particulate contaminants. As defined by the Institute of Environmental Sciences and Technology, IEST-RP-CC001.3 and MIL-STD-282 Method 102.9.1, a HEPA filter must capture a minimum of 99.97% of contaminants at 0.3 microns in size. The 0.3 micron benchmark is used in efficiency ratings, because it approximates the most difficult particle size for a filter to capture. HEPA filters are even more efficient in removing particles that are smaller than 0.3 microns and larger than 0.3 microns. This type of filtration has its own fan and can be installed as a stand alone unit or it can be installed to work in conjunction with your central a/c and heating system.

 

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