Selecting the Right Air Filter

by | Apr 30, 2017 | HVAC Blog

The original purpose of air filters was to protect the coils from getting caked with dust, dirt and debris. The coils simply can’t exchange heat, and therefore can’t cool, if they are covered with dirt. More efficient air filtering will not only protect your HVAC system but will also deliver cleaner air to breathe. Your decision is based on what you are wanting to achieve. If you are thinking about minimizing costs at your rental property or in your shop you may choose a basic air filter to protect your equipment. If you want a cleaner home and fewer colds you may choose a high-tech filtration system. There are several reasonable choices which fall in-between. It is helpful to know how filters work.

When choosing an air filter, it is helpful to understand the filter 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.

Also, there are two basic types of air filters:

A. Mechanical air filters remove airborne particles by blocking and capturing them on a filter medium.
B. Electronic air filters use an electric field to attract and trap particles to the media like a dirt magnet.

A. Mechanical Air Filters

Mechanical air filters commonly used with most heating and air conditioning systems have a MERV rating of 1-4. Basic flat or pleated disposables or 1-2-inch fiberglass filters simply protect the HVAC equipment from buildup of dust and grime on critical heat transfer surfaces by removing large particles that are light enough that they remain airborne (and not settled on your furniture and carpeting). Most contractors, however, recommend at least a minimum of one inch pleated filter to protect your equipment. To simply protect your equipment flat filters must be replaced every 1-3 months, depending on how dusty the environment is and only cost a couple of dollars. The advantage of using simple flat filters is they are inexpensive insurance protecting your equipment -as long as they are changed out regularly. They work well for renters and people without pets, allergies, asthma, smoking or lung disease. They do not clean the air you breathe.

Disposable pleated cotton or polyester mechanical filters, which have a MERV rating of 6, are more efficient at removing large and some medium-sized particles like spores and mites. They are not very efficient at getting rid of small particles which remain suspended in the air longer and fly right through simple filters. Pleated filters generally need to be replaced a little more frequently than flat filters to avoid clogging-up precisely because they are more efficient. Pleated filters should be changed monthly when there are pets in the home or at least 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 creates more air flow resistance, making your system use more energy and be more expensive to operate. Smaller particulate, which may irritate respiratory conditions, are not captured by these filters.

If you or someone you care about has breathing problems worsened by dust the professionals at Oasis can help. Have questions about air quality?
Call Oasis at (520) 648-1755!

Keeping in mind efficient filters get dirty quicker and dirty filters restrict air flow making your unit work harder, to more efficiently remove smaller particles such as viruses, bacteria, some mold spores, cat and dog dander, consider the following options:

1. Use a Medium-Efficiency Filter
A five inch higher-efficiency filter is a cost-effective upgrade to the standard one inch filter routinely used and 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 replacement 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 decrease indoor particulate concentrations about 80 percent – making breathing easier for people with allergies.
2. Electrostatic Filter
With a MERV rating of 10, disposable electrostatic filters contain self-charging electrostatic cotton or paper fibers that act like magnets, attracting and trapping small particles, making them a good choice for homes with children, pets and smokers. While the cost is affordable, at about $10 in standard sizes, custom sizes can be expensive if they are replaced 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 removable and machine-washable filter that can be cleaned once-a-month and reused for six to eight years. They are made from deep 4-5″ pleated polyester attached to a 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 inexpensive disposable filters will work well, costing less in the long run. Care must be taken after you wash permanent 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!

3. ‘High-Efficiency’ Permanent Electrostatic Filters
This super-charged reusable electrostatic mechanical filter is MERV rated 8-16 costing around $100/ year. Some of them are large enough to look like true HEPA filters and they are often confused with them. The high filtration 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 its thick size.
4. Carbon Media Filter
The carbon media filter is a special kind of furnace filter that works on a molecular level to help reduce unwanted odors and dust in your home’s heated 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 tiny cracks in the carbon to allow maximum absorption. Replaced every 2-3 months, they are rated MERV 8 and cost $10-30 each, depending on size.
5. HEPA (High Efficiency Particulate Air Filter)
If you are very 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 can cause extra wear and tear on the blower motor and may age your HVAC equipment prematurely. Installation of HEPA filters in a residential HVAC system usually requires professional modification.

If indoor air quality is important to you,
call Oasis at (520) 648-1755

Let us help you select the right filters or a whole-home air filtration system to fit your needs.

B. 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 clean all the air in your home. All particles, large and small, are eclectically positively charged as they pass through and are then collected on a negatively charged collection interface. This process of ionization produces a very small amount of ozone which some people might 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 of 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 heating and cooling system will continue to circulate dirty air throughout your whole house. You know this equipment is inefficient when you see that thick layer of dust on your furniture!

Your needs are unique! Let Oasis Help You!

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.
(520) 648-1755

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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