Air Conditioning Filters:
Filter in Comfort, Filter Out Cost
The single most important thing you can do to keep your air conditioning and heating system working efficiently is to make sure the air filter is matched to the unit and is clean. Air filters can also provide other benefits such as cleaner air and reduced allergy symptoms.
Air Filtration: Return to Top
Function - Originally the primary purpose of air filters was to keep system components (blower and evaporator coil) clean. Clean air to breathe was a fringe benefit. Now, more attention is given to cleaning the air we breathe.
Condition - A dirty filter or a filter that is too small can have many negative effects:
- Increased blower power consumption.
- Reduced cooling or heating.
- Compressor Failure.
- Result-higher cost, shorter equipment life.
How Often to Clean or Replace?
This can vary greatly. It can range from one to two months for most homes to every couple of weeks for some businesses. Don't wait for the entire filter to become matted with dust. If most strands of fiberglass (or other material) are coated with dust, it's time to replace it (or clean it, if applicable). Some filters clog more quickly than others.
What Size Filter?
As a general rule, you should have 1 1/2 square feet of filter for each ton of capacity. One square foot should be considered an absolute minimum.
How well a filter cleans the air depends on the filter, what is in the air and the airflow through the filter. Cleaning ability should be compared on the basis of standardized tests designed to test the filter's efficiency on the size of particles important to you.
Types: Return to Top
Conventional 1" fiberglass throwaway filters
Found in most residential and small commercial applications. Lowest first cost, but least effective. Many are coated with an adhesive substance to
help collect dust. For this reason, this type of filter should not be cleaned in any way to "extend"
its life. The dust and adhesive are both removed when cleaned, rendering the filter almost useless.
Conventional 2" fiberglass throwaway filters
Commonly found in some commercial applications. Although it is twice as thick as a 1" filter, it is not twice
as efficient; it only holds more dust.
The same characteristic that makes a filter more efficient may require more blower power and could possibly overload your blower and reduce airflow through the system. Check with your service contractor before using nonstandard filters. Before purchasing any air filter, particularly "high efficiency"
filters, be certain that it is properly sized for your system. Because "high efficiency filters" may have more
resistance to airflow, they may have to be larger in square footage than standard types. Also, it doesn't matter how
efficient your filter is, if the air return duct is not thoroughly sealed against air leaks; unfiltered dirty air
will enter the air stream. The dirtier or more restrictive the filter, the more air will come in the return leak.
This air is often hot, humid, attic air, which increases the work of the air conditioner, decreases the comfort and
increases your cost.
Pleated 1" and 2" fiberglass throwaway filters
The 1" version can be used in most residential and commercial applications. The fiberglass material
is normally more densely woven to increase efficiency. Its pleated surface greatly increases dust collection area
and thus extends its useful life.
Permanent mesh filters
These come in 1" and 2" versions and are made from different types of materials and consequently have a wide variety of effectiveness. Some of the
older types such as aluminum mesh are no more effective than good fiberglass filters. These require the application of a filter adhesive spray after cleaning
(washing) and drying. The filter adhesive should be available where you buy the filter.
These cleanable filters also come in 1" and 2" versions. Most filters advertised as allergy free are of this
type. There are many different designs, and performance can vary. Some manufacturers claim very high efficiencies, but keep
in mind that different manufacturers may use different tests to determine efficiencies. If the tests are not the same, the
results may not be comparable. All electrostatic filter makers claim that the air movement through the filter creates a
static charge that collects very tiny particles of dust. Like their "permanent" counterpart, electrostatic filters
require frequent and thorough cleaning and may consume more blower power.
Cleanable permanent filters should be sturdily constructed of quality material and be easy to clean. It may be
wise to see a demonstration of cleaning the filter before purchasing.
Electronic filters are always connected to an electrical power source. Although some
versions can be installed into a standard wall-mounted filter grill, many require>
installation into the air return duct. They usually come with a pre-filter, which collects the
larger particles of dust and, therefore, reduces the frequency of cleaning the main filter
cell. The pre-filter has to be cleaned about once a month, but the main filter may go as
much as six months between cleanings. These are the most efficient, and most expensive,
of all-residential filters.
Other specialized filters such as activated carbon for odor control are
available. Consult your service professional for special needs.
Installation: Return to Top
Filter installation is important. Many filters have arrows indicating the correct airflow direction. These filters should
be installed so that the air will flow in the same direction as the arrow. If there is no arrow, the strongest part of the
filter (often reinforced with metal grid) should be next to the air conditioning system so that the air exits at the reinforced
part of the filter. Correctly installed, the filter should fit tightly and securely. If the filter does not stay in place
during operation, it will not be effective.
For additional information, consult your county agent or home economist at your local Cooperative Extension Service office.
J. David Bankston, Jr., PhD., Specialist (Engineering)
Mike Carl, Computer Programmer
Metro Area Energy Advisory Committee
Visit our website: http://www.agctr.lsu.edu/wwwac
Louisiana State University Agricultural Center, William B. Richardson, Chancellor
Louisiana Cooperative Extension Service, Jack L. Bagent,
Vice Chancellor and Director
Pub. 2411 (5M) 10/98 Rev.
Issued in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, in cooperation with The United States Department of Agriculture. The Louisiana Cooperative Extension Service provides equal opportunities in programs and employment.
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