With all of the information circulating on the internet today concerning indoor air quality one primary way to control what we breathe in our house is to filter our air very well. Most air-conditioning systems installed today in new homes use standard disposable filters unless the homeowner has specified a higher grade of filtration at the time of the air-conditioners installation and paid for this feature. Well-meaning consumers having learned of the value of better air filtration on indoor air quality flock to home improvement centers to buy better quality filters for use in their heating and cooling system. The problem is these filters may be killing both your air-conditioning and your electric bill!
Air-conditioning systems are designed in an ideal environment on a set of blue prints by an engineer who calculates the exact CFM or cubic feet per minute of air that is required to enter a room to maintain it at a set temperature and encourage air movement. This design of the air distribution or duct system is perhaps the most understated aspect of having a comfortable and healthy home. The design of the engineer in an office rarely if ever translates from the drawing to the reality of the actual installation in the field due to a multitude of variables. In residential homes the space in an attics, between floors, and crawl spaces is often filled with electrical wiring, gas piping, plumbing, ventilation systems, and structural supports that require all trades to reroute their materials to deal either with the preceding trade that worked on the home or the design of the structure that may not have been accurately reflected in the blue prints.
Most air-conditioning contractors understand this dilemma will be faced in the field by their installers and so they have a tendency to over design the duct system for maximum performance if the installation varies from the drawn prints. The problem occurs in that many homes built throughout the years have never had their air distribution system tested to see if they fell within the parameters of the design by the engineer. Even though engineers make over design to compensate for installation issues the installers may also have to make compensation for not being able to run the duct work as originally designed.
This creates even more air friction which reduces the efficiency of air delivery into various areas of the home. Poor installation techniques along with damage done to the air distribution after the inspection by the municipal authorities overseeing the construction of a home may lead to leakage in the ductwork that also creates problems with the air distribution system. Air distribution systems that are not delivering the proper CFM throughout the home typically indicate an inadequate airflow through the blower assembly, leaks or restrictions within the air distribution system, or a compromise of the initial design. Sadly however, most homeowners will never know whether their duct system functions as designed by the engineer.
Now what you may ask does this have to do with the type of filter that I choose for my home improvement center to install on my heating and air-conditioning system? It has an enormous impact! If in their distribution system the blower is not moving the proper amount of air then there is a strong probability that on the air-conditioning side the system is not charged properly with refrigerant. Almost all charging charts from the manufacturers for refrigerants are based on the assumption that the blower unit is moving a specific CFM within a given tolerance of error. If this is not the case then the charging recommendations from the manufacturers are never correct.
If the air distribution system was already operating with a cheap disposable filter at a marginal design level, then the introduction of a higher quality filter, which while possibly improving the air quality may also reduce the airflow, will exacerbate the problem creating even a greater challenge for a service technician to properly balance the refrigerant charge in and air-conditioning system. Improper refrigerant charge in an air-conditioning system is the leading cause of premature compressor failure, excessively high utility bills, and an uncomfortable environment within the house due to the poor performance of the air-conditioning system.
Many tract homes were built with a single central air conditioning and heating return. In this case adding a higher filtration filter can dramatically impede the airflow as the filter surface loads between the times that it is changed by the consumer or the air-conditioning contractor. Surface loading is where the face of a filter loads with dust and as it does airflow across the filter drops creating even less air for the blower unit to move to other portions of the home even though the efficiency of the filter increases because of the increased surface area that the air has to pass through.
Since higher quality air filters, not air cleaners, reduced to varying degrees the amount of air flow through a heating and air-conditioning system it is imperative that you understand the impact of utilizing a higher efficiency filter such as a pleated filter, electrostatic filter, or even in some cases a bag filter before you go to a home improvement center purchase one and then added to your air-conditioning or heating system. Filters that are advertised as HEPA filters typically have a much higher impact on airflow than other types.
To understand the impact of a higher quality filter on an air distribution system think of what happens if you apply a sheet of paper across the back grill of a floor fan. The airflow coming out of the fan will be dramatically reduced thus creating a greater load on the fan motor which increases its electric consumption and at the same time creates unneeded wear that will reduce its operational life. At the same time since the fan is designed to move a specific amount of air in attempts to draw air from any available area to get around the blockage. In a duct system this means that areas of leakage in the duct system that were previously considered small will now be increased in magnitude as the system tries to pull as much air as possible past or around the higher efficiency air filter. In some cases air quality in the home drops as particulates are sucked into the duct system downstream from the filter through duct leakage due to the high resistance of the new air filter.
Custom-built homes that utilize multiple returns throughout the house may suffer a lower incidence of duct leakage, excessive utility bills, and premature compressor failure with the addition of higher quality filtration, but it still requires good judgment and the knowledge of whether or not you're air distribution system is functioning as designed.
Many well-meaning air conditioning contractors recommend higher quality filtration system to be added onto an air conditioner or heating system at the time that the system is replaced without giving adequate consideration to the duct work that already exists in the home. If you are considering changing your air-conditioning system then you should insist that your contractor provide a test and balance of the air distribution system after the installation of the replacement heating and cooling unit. This procedure ensures that the air delivery across the blower unit as well as into each condition space within the home meets the design requirements of the engineer.
So how to I increase the quality of filtration in my home without sacrificing all my utility bills, or risking future damage to my air-conditioning or heating system? The answer lies in having qualified Service Company test and balance your air distribution for your home so that it meets not only the manufacturer's requirements but also the design of the original air-conditioning design. During this process additional return air ducts may need to be added if necessary to see that increased filtration does not reduce the amount of air flow required across the heating or cooling unit. In some cases your home may be too old for the original design to even be available. In this case a reputable air conditioning and heating contractor can create a design based on the parameters of your home and then match your air distribution systems performance to that design. This may require changes in duct work, sealing of leaks that have occurred over the years in your duct system, and even weatherization of your home in order to ensure that the air distribution system is functioning properly.
Even though it may sound attractive to purchase a higher quality filter and put it in our air-conditioning system to improve the air that we breathe in our home, due to the competitive nature of home building the design of an enormous amount of air-conditioning systems in use today is marginal at best. Adding a restrictive device to the airflow straight will create problems in the future that may far surpass the perceived health value of a better filter.
Higher quality filtration is indeed a necessity to improve air quality in your home. But before running out to your nearest retailer or home improvement center, or even asking your air-conditioning contractor to provide you with better filters, make sure that your duct system is designed to handle the increased load that a higher efficiency filter will put on it. Doing so may save not only your air conditioner, but your wallet as well by avoiding unnecessary utility consumption and breakdowns.
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