Indoor Air Quality (IAQ)

Improve the indoor air quality of your home by knowing which type of air filter is best for your health, your HVAC system and your home. The air filter in your home HVAC system plays a critical part in protecting your HVAC equipment as well as your health. The primary purpose of the air filter is to remove air borne particles of various sizes. There are two types of air filtration methods, mechanical and electronic. 

NOTE: The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRE) developed a rating scale to define the efficiency of different air filters. The Minimum Efficiency Reporting Value (MERV) ranges from 1 to 20. The higher the number, the more efficient the filter.

Mechanical Air Filters

Mechanical air filters improve indoor air quality by removing particles such as dust, pet dander, pollen and some mold spores from the air by capturing them on a media surface as the air flows through the filter.
The type of media varies depending on design and cost. Most synthetic filters are fiberglass or polyester. The size and amount of particulate matter that is captured depends largely on the total surface area that the air flowing through passes over and the density of the media within that area. Larger surface areas are capable of capturing more particles. Some filters may be electrostatically charged to attract and capture more particles.

Mechanical Air Filters

Flat/Panel filters

Flat or panel filters are considered low efficiency filters with a MERV rating of 1 – 4. They have minimal surface area by design, which also limits the density of the filter media. While these filters allow for good air flow through the system, they capture only larger particles, providing some protection for equipment but little to no air cleaning of potentially harmful airborne particles. They are inexpensive but require changing frequently, preferably once a month, when the HVAC system is active for an extended period.

Pleated filters

Pleated filters come in various sizes ranging from 1 to 6 inches in depth. They provide more surface area than flat filters and are considered medium efficiency filters with a MERV filter ranging from 5 – 16. They also present greater air flow resistance which could result in pressure drop. Therefore it’s recommended to check your HVAC manufacturer specifications to properly match the filter type and required air flow before installing any filter. Pleated filters are more expensive than flat panel filters but depending on quality may need to be changed less frequently. It’s still recommended to perform a monthly check for particle buildup on the surface.

Electrostatic filters

Electrostatic (washable) filters eliminate the need to purchase replacements like disposable filters. With MERV ratings from 1 – 11, they’re efficiency runs from low to moderately high. The lower MERV rated electrostatic filters (MERV 1 – 4) capture only larger particles. They require frequent manual cleaning and it’s important to strictly follow the manufactures cleaning instructions. If not thoroughly dried before reuse, moisture and dust buildup over time may result in the need for duct cleaning. They may have higher air flow restriction which can place additional strain on the HVAC system so they should be carefully matched to the air flow requirements of the HVAC system.

HEPA filters

HEPA filters provide maximum surface area and are capable of removing very small particles, .1 to .3 and larger microns. They have a minimum efficiency between 99.97 percent and 99.999 percent. They are considered high efficiency filters with a MERV rating between 17 – 20.  Many residential HVAC systems require modification to accommodate their increased dimensional size, which could prove quite costly. Some HVAC systems may have built-in accommodations for HEPA filters so always check with your HVAC system manufacture before purchasing.

IMPORTANT NOTES

Size Matters
All air filters come in various sizes so it’s important to purchase the correct size air filter for your specific application. If the filter is not sized properly, leakage can occur around the filter. An improperly sized filter may also result in unnecessary air flow restriction.

Air Flow Matters
Although higher MERV Ratings remove more air borne particles, they may also restrict air flow and reduce the efficiency of your HVAC system, resulting in higher operating costs and reduced equipment life span.

Recommendation
To insure the indoor air quality of your home, the best policy is to consult with your HVAC contractor to match the appropriate filter type and size to your HVAC system and to your specific health requirements.

Electronic Air Cleaners

Electronic air cleaners can improve your indoor air quality by electronically removing airborne particles or instigating the settling of the particles for easier clean up and removal.

There are two types of electronic air cleaners, electrostatic precipitators and ion generators. They share some operational similarities in that they both attract, capture and electrically charge airborne particles. However, where electrostatic precipitators use collecting plates, ion generators use either UV lights or a corona discharge to produce ions which attract and charge the particles, causing them to settle in their surrounding environment. Both types of cleaners may employ a reusable prefilter to capture large particles for removal before sending the air on to the ionization section.

Electrostatic precipitators 

An electrostatic precipitator works by attracting and drawing airborne particles through an electrostatic field where they receive an ionized charge. Air is pulled into an enclosed space known as an ionization section where the particles are negatively charged. These charged particles move to a collector where they come into contact with oppositely-charged metal plates that capture the particles. The clean air is then exhausted. 

As noted by the EPA:
“Electrostatic precipitators remove and collect small airborne particles and have an initial ASHRAE dust spot efficiency of up to 98 percent at low airflow velocity. This efficiency will be highest for clean electronic air cleaners. Electronic air cleaners exhibit high initial efficiencies in cleaning air, largely because of their ability to remove fine particles. Their efficiency decreases as the collecting plates become loaded with particles, or as airflow velocity increases or becomes less uniform.”

Ion Generators

Similar to an electrostatic precipitators, Ion generators, or ionizers, disperse charged ions into the air,  but without a collector. These ions attach to airborne particles, giving them a charge so that they attach to nearby surfaces such as walls or furniture, or attach to one another and settle faster.

Regardless of the type of filter or cleaner, all home owners should regularly check their HVAC systems filter to ensure that the system is operating at peak efficiency. Unfortunately, the average homeowner often fails to change or clean their filter as required which results in reduced operating efficiency and higher operating costs.

Regularly changing or cleaning (i.e. washable filters) your air conditioner’s air filter will increase the performance of your HVAC system and reduce it’s energy consumption. How much? According to epa.gov, anywhere from 5 to 15 percent.

Use your knowledge of air filters and cleaners to take control of your indoor air quality, improve your health and ensure your HVAC system is operating at peak efficiency.

A/C Repairs Inc.

How to Choose the Best Air Filter Video Recap