By Jeffery Hunt

Filtering the air in your home may seem like a fairly simple task, however, there is much more to selecting a filter than most homeowners and even some heating and cooling contractors realize.

The science of moving the air through your ductwork must be considered first. The fan or blower motor provides the work of turning the fan blade. The air in your home is pulled into the return grills and the return duct system; then moves through the heating and cooling equipment; and lastly, is pushed through the supply ductwork and grills back into the home as “reconditioned air”. Every component in this air flow path provides a measurable amount of resistance to the air flow. These components include the grills, ductwork, filters, and equipment. The design of the equipment and ductwork is beyond the control of the homeowner, and if properly designed by the contractor, should not present any issues that the fan cannot overcome.

The filter(s) in the system, however, are produced in a very wide array of materials, sizes, and can have varying locations. To properly explain filter selection, we first must provide parameters for both “ends” of the spectrum. On one end, let’s assume “no filter” at all. This would provide zero resistance to air flow at the filter location. On the other end, let’s assume something solid, like steel. This would provide total resistance to air flow at the filter location. Every heating and cooling filter available is somewhere between these two points on the spectrum.

As we select a “tighter” filter, we move closer to the steel example on the spectrum. We must be conscious of the fact that a tighter filter will reduce the amount of air flow, and cause the fan motor to work harder. It is possible, without considering this, that we can cause a reduction in heating or cooling capacity and efficiency by selecting too tight of a filter, or by failing to re-design the air flow system in order to compensate for the tighter filter. That doesn’t mean we cannot use tighter filters. If the material used is denser, then we can compensate by using a larger filter area. In other words, if your system uses a 20 x 20 x 1 standard filter that you can actually see through, and you wish to install a better filter, you may need to install a larger size so that the same amount of air can pass through to the blower. Here is where your heating and cooling contractor can help you decide the best way to accomplish this.

In many cases, the ductwork on the return side of the system may need to be increased in size to allow for the added resistance of the tighter filter. Sometimes, simply adding additional returns to the existing ducts will solve the problem. Your heating and cooling contractor has ways to measure this resistance and understands how to resolve the air flow issues.

In summary, simply installing a tighter filter of the same size that you currently use may be causing a bigger problem. You should consult your heating and cooling professional when considering filtration upgrades. If the system is designed correctly, you can install better filters without giving up comfort and energy efficiency, or damaging your expensive heating and cooling equipment.

Rhinohorn Sales LLC provides heating and cooling contractor services, such as employee skill training, business consultation, and shopping cart websites. Building value is an ongoing, constant evolution. Periodic training keeps skills sharp, and maintains focus on company values. For more information, visit

Jeffery Hunt is Co-Owner of Rhinohorn Sales, LLC, Products include contractor shopping cart websites, and other contractor business services. Rhinohorn Sales LLC owns HVAC Parts Online, Filters Today, Smart Contractor; and other websites offering heating and cooling parts, filters, and indoor air quality products.  He is also a State of Florida licensed Air Conditioning Contractor, and HVAC business consultant.

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