Why we Like Gasketed Air Filters & Dirt in HVAC Systems and
Effectiveness of Washable Air Filters InspectAPedia® -
Benefits of gasketed air filters on HVAC systems
Significance of dirt and debris in the return air plenum or ducts
Washable air filters for HVAC systems
Air conditioning / heating system filter product sources and recommendations
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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 "air cleaners" are generally ineffective in buildings.
We include photographs to assist readers in
recognizing cooling system defects. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. 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.
The Benefits of Gasketed Air Filters on HVAC Systems
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!]
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.
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.
The photograph shows a typical washable metal air filter. Other types of washable air filters are available as well.
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.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.
Use links just below or 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.
Thanks to Mark 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.
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
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
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"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]
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
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