Part 1: The Three Types of Air Filters HVAC's Impact on IAQ and Energy Efficiency IAQ   Article Use Policy The air-filtration industry has seen its share of changes over the last decade. Manufacturers have created new products that not only have improved indoor air quality (IAQ) but also have reduced the cost of installing and operating air-filtration equipment in commercial and institutional facilities. Besides technology improvements, industry organizations are adopting standards, guidelines and requirements that promote healthy IAQ. Debate continues on the impact IAQ can have on building occupants, including whether productivity and overall occupant health improves as air quality improves. As maintenance and engineering managers continue to focus on IAQ and its impact on their facilities and occupants, manufacturers are providing them with more efficient HVAC systems and components, including air filters. These technology advances include reduced pressure drops and improved filter efficiency, as well as smaller fans and motors, due to the reduced pressure drop across the filters.

When the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) introduced IAQ standards, it signaled an important change in the air-filtration industry. ASHRAE has been promoting the adoption of the minimum efficiency reporting value (MERV) system to standardize definitions of efficiencies.financing for hvac unit MERV measures a filter's arrestance — a filter's ability to remove large airborne particles from the air — and dust-spot efficiency — its ability to remove small airborne particles — and assigns a number based on the filter's ability to remove the particles. the best hvac booksSeveral types of air filters are common in commercial HVAC systems:air handling unit pressureThis throwaway air filter is the most common type.

Layered fiberglass fibers are laid over each other to form the filter media and typically are reinforced with a metal grating that supports the fiberglass to prevent failure and collapse. Polyester and pleated filters. These filters are similar to fiberglass filters but typically have a higher resistance to airflow and a superior dust-stopping ability. High efficiency particulate arrestance (HEPA) filters. These units filter the air passing through them at a very fine scale. The U.S. Department of Energy (DOE) and its contractors use HEPA filters that meet DOE standard STD-3020-97, Specification for HEPA Filters Used by DOE Contractors, to filter 99.97 percent of all particles 0.3 microns or larger.These products are not as common and rely on the build-up of dust along the cloth to improve the efficiency of the filter. Industrial processes involving high volumes of coarse dust are typical applications. Because filters are fairly simple — they essentially are porous membranes that allow air to flow through them — little change has occurred to improve problems associated with air pressure drop and its impact on energy efficiency.

Part 1: The Three Types of Air Filters Part 2: HVAC's Impact on IAQ and Energy EfficiencyPart of responsible homeownership includes, of course, regular home maintenance.  And there are some tasks that, if deferred, can lead to a home system that’s inefficient and overworked, which can result in problems and expenses.  One such task is changing the filter of the home’s HVAC system.  It’s simple and inexpensive, and taking care of it at least every three months can mean the difference between optimum comfort and avoidable repairs. Most homes have some sort of furnace or heat pump, and many of those homes (especially newer ones) have combined heating, ventilation and air-conditioning or HVAC systems.  Each type uses some type of air filter or screen to prevent larger airborne particles (up to 40 microns) from entering the system and clogging sensitive machinery.  A system that has a dirty filter can suffer from pressure drop, which can lead to reduced air flow, or “blow-out,” resulting in no air infiltration at all. 

Any of these conditions can cause the system to work harder to keep the home warm or cool (depending on the season and the setting).  And any mechanical component that has to work harder to run efficiently puts undue stress on the whole system, which can lead to premature failure, resulting in repair or replacement. Also, a dirty filter that’s exposed to condensation can become damp, which can lead to mold growth that can be spread throughout the home by the HVAC system.  This can lead to serious health consequences, not to mention a compromised unit that will likely require servicing and may require replacement, depending on the severity of the moisture problem. Most HVAC and furnace filters are disposable, made of biodegradable paper or similar media, and shaped in cells, screens or fins designed to trap as much airborne debris as possible.  Filters can typically be purchased in economical multi-packs, and there are many types that will fit different models of furnace/HVAC units. 

It’s important to use the appropriate filter for your unit; using the wrong filter that doesn’t fit the unit properly can create the same types of problems as having a dirty filter.  Your HVAC installer can show you where the filter goes and how to remove the old one and install a new one.  Your unit may also have an affixed label with directions for easy filter replacement. Your HVAC or furnace technician should service your unit once a year.  Because a furnace/HVAC unit contains moving parts, it’s important that belts are not cracked and dry, ventilation ductwork is not gapped, cracked or rusted, and components, such as coils and fans, are clog-free and adequately lubricated for unimpeded operation.  This sort of evaluation is best left to the professional, unless the homeowner has had the appropriate training. The filter of the unit, especially if it’s an HVAC unit that will tend to get nearly year-round use, should be changed by the homeowner at least every three months, but possibly more often.