Why We Like Gasketed Air Filters & Dirt in HVAC Systems and
Effectiveness of Washable Air Filters
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Gasketed air conditioner or heating filters, leaky air filters, washable air conditioning or heater air filters: This article explains and explain leaky air filters and the value of gasketed air filters, followed by comments on the effectiveness of washable air filters.
This website answers almost any question you might ask about air filters for heating or air conditioning systems. We explain how an air conditioning service technician will diagnose
certain common air conditioning system failures or defects. In these articles we are referring to filters installed on central air conditioning or central heating systems that move air through air handlers and duct systems. Standalone or portable "air cleaners" or "air purifiers" are generally ineffective in buildings. We include photographs to assist readers in
recognizing cooling system defects.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
The Benefits of Gasketed Air Filters on HVAC Systems
Readers should also see our INDOOR AIR QUALITY IMPROVEMENT GUIDE article series.
The page top photograph is of a low-MERV HVAC filter in an air handler.
A gasketed heating or air conditioning system air filter improves the filter effectiveness. The benefits of a high efficiency air filter material when used in an air handler and duct system are not fully realized if air bypasses the filter around its
installation frame due to poor fit or poor installation.
[The filter shown here is not a high quality gasket-type air filter.] That's why some manufacturers emphasize the value of air-sealing gaskets on their products.
Simple observations made in the field will make for agreement with the manufacturers that filter bypass is an issue at some heating or air conditioning installations. When changing
an air filter at a return air inlet or at an air handler, when the old filter has been removed, take a look inside the return duct at the return register, or inside
the return plenum at the air handler, to see just how much debris is passing the filter.
[The photograph above shows how a badly-fit HVAC air filter can not only leak bypass air into the blower compartment but also it can collapse right into the blower fan - this is a potential fire hazard!]
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Implications of dust and debris in the return air plenum
On an old heating or air conditioning system where filters have been ineffective, not properly installed, leaky, or not maintained and changed on schedule, we often find quite a bit of debris entering the air handler
and duct system.
This is in fact so common that most HVAC installers and technicians consider dirty ducts to be "normal".
And they're quite correct: typical house dust that has collected inside of a duct system is not normally a toxic substance.
But
1) a high level of dust and debris inside of an air handler or duct system indicates that system filtration has not been effective,
2) the dust level indicates that the system has been delivering dust and debris to the occupants providing poorly-filtered air, and
3) there is an increased risk of mold in the
duct or air handler system if moisture enters the system from a leak or from air conditioning condensate mishandling.
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How Good are Washable air filters for heating and air conditioning systems
Washable re-usable air filters are very appealing from a cost viewpoint. I would look for data to indicate whether or not the washable filter runs at a lower MERV
or filtering efficiency.
In our cascaded filter proposal (discussed at this website) we included and continued to use a washable filter that came with the equipment since
it was not reducing the airflow CFM, but we preceded it with other filters for different purposes.
he photograph at above left shows a typical washable metal air filter used in central air conditioning systems, and at above right is a washable foam air conditioning filter used in a portable room air conditioner. Other types of washable air filters are available as well.
At left we illustrate a plastic and nylon washable air filter used in both window air conditioners and in wall-mounted split system air conditioner units.
Unlike the foam type air filter shown above, these plastic and nylon air filters withstand repeated cleaning without disintegrating.
The efficiency of these filters increases as debris begins to settle on the filter surface, but eventually the improvement in air filtration efficiency is offset by reduced airflow - so clean the air filters in accordance with the cooling unit manufacturer's instructions - typically monthly during constant use.
Also see Spit System Air Conditioner Air Filter Maintenance - How to Clean a Split System Air Conditioner Filter.
A metallic air filter (shown ) is not very efficient (effective) at trapping airborne particles when it is clean, though efficiency improves as it gets dirty. Other pleated, fabric or paper air filters that are also washable are more efficient at trapping airborne debris.
Be sure to read PARTICLE SIZES & IAQ for a description of
the sizes and behaviors of some of the common particles that are an indoor air quality concern.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
Click to Show or Hide Citations & References
- Thanks to AMark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects"
section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and
home inspection educator.
- Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
- Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
- Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
- "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
- Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard- Asbestos HVAC Ducts and Flues field identification photos and guide
- Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
- US EPA article on air filter efficiency: epa.gov/iaq/pubs/airclean.html 06/18/2010
- Wikipedia provided background information about the definition of HEPA and airborne particle interception.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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