Selecting the Right Filter

There Are Two Basic Types of Air Filters:

  1. Mechanical air filters remove airborne particles by capturing them on a filter medium.
  2. Electronic air filters use an electric field to trap particles like a dirt magnet.

MERV Filtration Rating System

When choosing a mechanical filter it is helpful to understand the air filtration rating system used in the HVAC industry. The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) has developed a measurement for air filters that is considered the industry standard. Air filtration efficiency is defined as how well the filter removes airborne particles from the air stream that passes through it and is measured by the “MERV” or minimum efficiency reporting value. MERV ratings range from a low of 1 to a high of 20.

Mechanical Air Filters

Mechanical air filters commonly used with HVAC most systems have a MERV of 1-4. Simple flat disposable or 1-2 inch fiberglass filters protect the HVAC equipment from the buildup of dust and grime on critical surfaces and offer moderate efficiency removing large particles, as long as they remain airborne and not settled on your furniture and carpeting. The advantages to using them is they are inexpensive, good for renters and people without allergies or asthma or lung disease. They do not clean the air you breathe. They simply protect the equipment and must be changed every 1-3 months depending on how dusty the environment is and only cost a dollar or two. However, most contractors recommend a minimum of one inch pleated filter to protect your equipment.

Simple disposable pleated cotton or polyester mechanical filters which have a MERV rating of 6 are efficient at removing large and some medium-sized particulate like spores and mites. They are not very efficient at getting rid of small particles which remain suspended in the air longer than the heavy particulate that settles on your furniture. These more efficient filters need to be changed more frequently to avoid clogging and overburdening your HVAC system. Pleated filters should be changed monthly when there are pets in the home or every three months when the system is running regularly. The advantages of using them are that they only cost $4-5, can be made of green materials and do actually clean the air you breathe of some small particles. Neglecting to change dirty filters adds more resistance to air flow, making your system use more energy and be more expensive to operate. Smaller particulate are not captured by these filters and may irritate respiratory conditions.

Efficient filters get dirty quicker and dirty filters restrict air flow making your unit work harder!
  • If you or someone you know has breathing problems worsened by dust the professionals at Oasis can help. Have questions about air quality? Call Oasis at (520) 648-1755!

To more efficiently remove smaller particles such as viruses, bacteria, some mold spores, cat and dog dander, consider the following options:

Use a Medium-Efficiency Filter- A five inch higher efficiency filter is a cost-effective upgrade to the standard one inch routinely used. It can be up to about 20 times more effective. Some studies show that medium-efficiency filters, with MERV ratings of 7 to 13, achieve the best balance between ability to filter small particles and allergens and filter cost. They are built with 1 to 6 inch pleats. The Environmental Protection Agency (EPA) says for some small particles, a medium efficiency filter rated MERV 13 will decreases in indoor concentrations about 80 percent making breathing easier for people with allergies.

Electrostatic Filter- With a MERV rating of 10, disposable electrostatic filters contain self-charging electrostatic cotton or paper fibers that attract and trap small particles making them a good choice for homes with children, pets and smokers. While the cost is affordable, about $10, in standard sizes, custom sizes can be expensive if they are changed according to recommendations.

Permanent electrostatic filters are similar to disposables in that they contain self-charging cotton or synthetic fibers which attract particles, but they have a machine-washable filter that can be washed once a month and reused for six to eight years. They are made from deep 4-5″ pleated polyester attached to very rigid metal grid to prevent leaks or fluttering. The deep pleats increase the collection surface area making these filters more efficient at capturing airborne particles. The MERV rating is 4-8 depending on the depth of the collection surface, somewhat less effective than disposable electrostatic filters but permanent electrostatic filters are environmentally friendly, have little waste, are affordable at $15-20, and could be a good option for standard sizes. Even the most expensive disposable filters will work well, costing less in the long run. Care must be taken after you wash these filters because if you re-install them while they’re still damp, they may grow fungi which may cause odors and your system could blow spores throughout your home.

  • Have an odor problem? Need help? Call Oasis at (520) 648-1755!

High-Efficiency Permanent Electrostatic Filters- This super-charged mechanical filter is  rated MERV 8-16 with a cost around $100/ year. Some of them are large enough to look like true HEPA filters and they are often confused with them. The advantages are appreciated in hospitals where they are used to filter out the smallest particles, helpful for those with respiratory problems or autoimmune disorders, and essential in preventing airborne transmitted infections. These filters create less airflow resistance compared to HEPA filters and support quieter operation of the blower fan. They must be professionally  installed in a special housing due to thick size.

Carbon Media Filter- This is a special kind of furnace filter that works on a molecular level to help reduce unwanted odors as well as dust particles in your home’s air because of its ability to catch very small particulates in its crevices.  “Activated carbon” means the media was super-heated to open up the cracks in the carbon to allow more absorption. They last 2-3 months) and filters at a level equal to a MERV 8. They are $10-30 each depending on size.

HEPA or High Efficiency Particulate Air Filter- If you are concerned with efficiently removing airborne irritants, HEPA filters are recognized by the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) as the definitive solution in purifying the air. HEPA filters, with a MERV of 17-20, block very fine particles down to 0.3 microns, catching 99.97% of dust, smoke and bacteria. Decreased airflow through very tight restrictive filters causes extra wear and tear on the blower motor and may cause your HVAC equipment to age prematurely. Installation of HEPA filters in a residential HVAC system usually requires a professional modification.

  • If indoor air quality is important to you, call Oasis at (520) 648-1755 and let us help you select the right filters or a whole-home air filtration system to fit your needs.

Electronic Air Cleaners

Whole house electronic filters, also called electronic air cleaners, are 3 stage units which are retrofitted into your ductwork and electrical system by your HVAC professional to all the air in your home. All particles, large and small, are eclectically positively charged as they pass through and are collected on a negatively charged collection interface. This process of ionization produces a very small amount of ozone which some people find irritates their respiratory system. Electronic filters are great at filtering out very small particles and cigarette smoke. Electronic filters are permanent, meaning there is no filter disposal but the collection plates need to be washed every 2-3 months.

Portable air cleaners are another example an electronic filter. While portable air cleaners are popular, they are inefficient because they only clean air in the room in which they are located. Your will heating and cooling system continues to circulate dirty air throughout your whole house. You know this is inefficient when you see that thick layer of dust on your furniture!

Let Oasis Help You!

Your needs are unique! We can help you find just the right solution for your situation and budget. In addition to air filters Oasis can help you improve the quality of the air in your home with duct cleaning services, humidifiers, air purifiers and ultraviolet germicidal lights to enhance the efficiency of your ventilation system. We’ll keep your air quality equipment running like new so you have healthy air in your home free of contaminants.

Call Oasis Cooling & Heating, Inc. at (520) 648-1755

to learn more or to schedule your next appointment.


Gardner, C. (2012). How the choose the right furnace filter. Bob Vila.

Is a washable air filter any better than a disposable air filter? (May 19, 2015). QHC NYC.

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