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Guide to Types of Indoor Air Filters, Air Cleaners and Air Purifiers InspectAPedia®  -     Guide to types of air cleaners used for Improving indoor air quality Table comparing types of air cleaners and their efficiency in removing different types and sizes of particles: flat air filters, pleated air filters, electrostatic air cleaners, electronic air cleaners, & HEPA air filters. Guide to filters for removing gases from air Air cleaner & air filter maintenance schedule table

Here we discuss the types of air cleaners or air purifiers used to improve indoor air quality in homes. We include a table of types of air cleaners and the types of particles they handle. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Our page top photo shows that even the naked eye can see comparatively large airborne particles indoors. But many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals. See ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY for our full list of environmental hazard identification and remedy related to buildings

© Copyright 2009 Daniel Friedman, Steve Bliss, Wiley & Sons, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Air-Cleaner Types

Table 7-2 Particulate Air Cleaner Comparison

Best Practices Guide to Residential Construction explains:

There are three main types of particulate air cleaners on the market: mechanical filters, electrostatic filters, and ion generators. In addition, there are filters with adsorbents, such as activated carbon, that are capable of removing certain gases (See Table 7-2 above) Most filters are available as standalone units or as add-ons to the home’s HVAC or ventilation system. Some hybrid systems on the market combine two or more strategies, such as a filter to remove particles plus activated carbon to remove odors and organic gases.

Mechanical Filters. These use a matrix of fiberglass or synthetic fibers and resin to filter particles out of air passing through. Some are coated with an oil or adhesive to help trap particles, and others have a static electrical charge. Some types of mechanical filters can be cleaned, but most need to be replaced when full. As mechanical filters clog, they become more efficient at trapping particles, but airflow is reduced. They can either work in stand-alone units or be incorporated into the HVAC or ventilation system.

• Flat filters are the standard fiberglass elements found in furnaces and air handlers. They are designed to catch large dust particles and have little effect on the smaller respirable particles that affect health.
• Pleated filters, or “extended media” filters, have smaller pores designed to capture small- and medium- sized particles. They are pleated like automobile air filters to provide greater surface area for improved airflow. Some will fit into a standard furnace filter slot, but the higher-efficiency types are generally too thick and require ductwork modifications. For good performance, they need to be replaced regularly.
• Electrostatic filters use a plastic element that is permanently charged with static electricity or captures an electric charge from the passing air. They are a little more effective than a standard furnace filter at capturing larger particles such as pollen and mold spores, and can be washed and reused when full.
• HEPA stands for “high-efficiency particulate accumulator.” These filters range from 95% to over 99% efficient for particles over 0.3 microns, including mold spores, mites, pet dander, and some viruses. Because of their high resistance to airflow, HEPA filters typically require a separate fan and housing. Replacement HEPA Filter elements last a year or longer but cost well over $100 versus $10 to $20 for a medium-efficiency pleated filter. Most have a prefilter to catch large particles that would prematurely clog the filter. Prefilters need to be changed regularly.

Electronic (Electrostatic) Air Cleaners

Electronic air cleaners (EACs) use a series of electrically charged metal plates or media filters to pull particles out of the air stream. They are either portable units designed to clean the air in one or two rooms or central systems connected to the return ductwork of the HVAC system. EAC systems create little resistance to airflow but require a separate fan, which along with the electrical charging device use about 30 to 50 watts of electricity.

Electronic air cleaners are highly efficient at removing both small and large particles, but require more maintenance than many homeowners would like. To remain effective, the filters must be removed regularly and hosed down in a large sink or tub. Some are designed to fit in a dishwasher.

In charging the particles with high voltage, EACs also produce small amounts of ozone, which can be an eye or respiratory irritant at high levels. Most people are not bothered by the amount produced. If this a concern, however, look for a unit with an activated carbon filter to remove the ozone.

Negative Ion Generators to Clean Indoor Air

These work by releasing electrically charged ions, which attach to dust particles in the air causing them to settle on walls, ceilings, furniture, and draperies. Placed too near a wall, they might leave a smudge of particles. Some units contain an optional collector to trap the charged particles in the unit, functioning similarly to an EAC.

Over time, however, the particles can lose their charge and reenter the air. Like EACs, they produce small amounts of ozone. There is little scientific evidence supporting the effectiveness of these units.

Do not rely on ozone generators to correct indoor air quality issues, and beware of ion generators that may be adjusted to produce high levels of indoor ozone. See OZONE AIR PURIFIER WARNINGS and see OZONE HAZARDS.

Turbulent Flow Precipitators to Clean Indoor Air

The turbulent flow precipitator (TFP) is a new proprietary technology from Canadian-based Nutech Energy System. The device, which attaches to the return ductwork of an HVAC or ventilation system, contains a fan and a labyrinthine core made of aluminum plates and synthetic fibers.

Turbulence in the air flings the suspended particles out of the airstream where they are trapped by a primary and secondary core, which need replacement in one and three years, respectively. Nutech claims that TFPs will capture 99% of particles larger than 5 microns, 97% from 2 to 3 microns, and 90% from 0.5 to 0.9 microns. A TFP unit with HEPA filtration is also available.

Gas Removal Filters to Clean Indoor Air

To remove gases, such as formaldehyde, combustion fumes, or volatile organic compounds, from the air requires the use of special adsorption media. These media contain materials, such as activated carbon or aluminum oxide, which trap the gases in tiny pores. Different chemical adsorbents are effective with different gases, and none is effective with every gas found in the typical home. Relatively small quantities of activated charcoal can be very effective at reducing odors, but how well they filter out the low levels of multiple chemical compounds typically found in household air is unclear.

In general the rate of adsorption of a gas is reduced as more of the target gas is captured in the filter media. Researchers have also found that, in many cases, some of the gas is reemitted from the filter back into the air. Scientific evidence about the real-life usefulness of these filters in homes is very limited.

-- Adapted with permission from Best Practices Guide to Residential Construction.

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• Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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ENVIRONMENTAL HAZARDS GUIDE
AIR POLLUTANTS, COMMON INDOOR
ALLERGEN TESTS for BUILDINGS
ALLERGENS in BUILDINGS, RECOGNIZING
ALLERGY TESTS for PEOPLE
ALLERGY TEST ACCURACY
FLOODS IN BUILDINGS-priorities
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
MOLD: A COMPLETE GUIDE TO MOLD
ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
  Health Effects of Air Pollutants
  Common Indoor Air Pollutants
  Key Strategies for Improving Indoor Air Quality
  Whole House Ventilation Strategies
  Exhaust-Only Ventilation
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  Balanced Ventilation
  Air Filtering Strategies
  Particles in Indoor Air - Chart
  Quick Guide to Gases
  Air-Cleaner Types
    Particulate Air Cleaner Table
  Air Filter Effectiveness
  Real-World Effectiveness of Air Cleaners
  Finding & Reducing Air Pollutants
  Radon Hazards
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  Biological Pollutants
  Volatile Organic Compounds VOCs
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  Carpeting and Indoor Air Quality
  Combustion Appliance Contaminants
  Backdrafting Appliances
  Fireplace & Woodstove Contaminants
  INDOOR AIR HAZARDS TABLE
  INDOOR COMBUSTION PRODUCTS & IAQ
INDOOR AIR QUALITY METHODS COMPARED
LEAD POISONING HAZARDS GUIDE
MOISTURE CONTROL in BUILDINGS
MOLD ACTION GUIDE - WHAT TO DO ABOUT MOLD
MOLD ATLAS & PARTICLES INDEX
MOLD BY MICROSCOPE
MOLD CLASSES, HAZARD LEVELS
MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD
MOLD DETECTION & INSPECTION GUIDE
ODORS, Smells, Gases in Buildings-Diagnosis & Cure
RENTERS & TENANTS GUIDE TO MOLD
SEWAGE BACKUP TEST & CLEANUP
STAIN DIAGNOSIS
TECHNICAL & LAB PROCEDURES
THERMAL TRACKING

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

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• Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Wiley.com and also at Amazon.com. See our book review of this publication

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