Maintaining indoor air quality through HVAC preventative maintenance and routine filter changes

Heating & air conditioning filters can be grouped into different categories depending upon how they capture airborne contaminants. The most common and least expensive filters are mechanical filters which are described below. If a passive electrical charge is added to a mechanical filter to assist in attracting airborne contaminants, it is then referred to as an electrostatically charged filter. If rather than a filter media, collection plates are used to attract and capture airborne contaminants, the filter is called an Electronic Air Cleaner (EAC). And finally, pre-charging of airborne contaminants can be combined with an actively charged filter media, to create an actively charged filtration system. It is important to select a proper filtratation system for your work and living areas, location plays a large role in your choice and also determines the amount of maintenance that is required.  At SD ATLAS HVAC we are able to assist you with all of your commercial, strata and residential HVAC filtration needs and help you improve your indoor air quality through scheduled HVAC preventative maintenance programs. We also specialize in HVAC service and repairs to keep your equipment running as efficient as possible.


Mechanical filters remove dust by capturing it on the filter element also known as the filter media. Such filters are often referred to as panel filters because they look like a panel of filter media held in a cardboard frame. The effectiveness of this type of filter is determined by the chance that a dust particle will collide with one of the fibers in the media, and the ability of the fiber to hold the particle. There are three different processes by which a mechanical filter works: impingement, interception and straining.  Impingement is the main process that captures large particles. Air passing through the filter is routed around the filter’s fibers. Large particles, however, do not follow the air streamlines around the fibers due to inertia. Rather, they move straight ahead colliding with the filter’s fibers and become attached. Interception occurs when a dust particle comes into contact with the fiber because the particle has followed the air streamlines. Another form of interception is the diffusional effect, which explains the capture of smaller particles. Because the small particles do not contain much mass, they are affected by the bombardment of air molecules that cause them to take an erratic path, which increases the route through the filter, increasing the chances that the particle will collide with a fiber. Straining is the filtration effect where the size of the particle is larger than the distance between the fibers (like a coffee filter).


Filters are given their rating by the term “MERV” or Minimum Efficiency Reporting Value. It is a number from 1 to 16 that is relative to an air filter’s efficiency. The higher the MERV rating, the more efficient the air filter is at removing particles. The lower end of the efficiency scale is the fibreglass panel filter that has a MERV rating of 1 to 3. On the higher end a MERV 14 filter is typically the filter of choice for critical areas of a hospital and this prevents transfer of bacteria and infectious diseases. Higher MERV filters are also capable of removing higher quantities of extremely small contaminant (particles as small as 1/300 the diameter of a human hair). A higher MERV rating filter has more resistance to airflow because the filter media becomes denser as efficiency increases. For the cleanest air, the highest MERV rated filter that the HVAC equipment is capable of forcing air through, based on the fan power, is what should be selected to create the optimal indoor air quality.


A typical 1-inch coarse filter provides protection for only the largest particles (10 microns and larger). These filters are designed only to protect the furnace or fan coil from bulk dust that can clog the cooling coil or otherwise decrease heat transfer efficiency. Because of the inability of these filters to capture smaller particles, they do very little to improve indoor air quality. These basic filters are generally a MERV rating of 1 to 3.


These filters typically have a MERV rating of 4-5. Although they are an improvement over a low-density coarse filter, they can capture some of the larger particles found in household dust. These filters can commonly be found as replacement filters in home improvement stores.


For a more effective air cleaning capability than standard 1-inch filters, box or cartridge filters may be used. These filters are typically MERV 8 to 13. They have the ability to capture particles with some efficiency down to 1 micron. In addition to being more effective in capturing smaller particles, pleated filters have the advantage of having greater holding capacity due to increased surface area. This extends the life of the filter. Typically these filters achieve a MERV 9 rating.


Electronic air cleaners differ considerably from mechanical “panel” filters. EACs use high-voltage electrodes
installed between grounded plates to create an electrostatic field imposing a charge on the dust particles as they pass by the plates. The particles are then attracted to oppositely charged collector plates. Several factors affect the ability of an electronic air cleaner to remove dust: particle size, velocity, voltage, plate spacing and ionizer spacing. Electronic air cleaners require occasional cleaning of the collector, or grounding plates. While this requires additional maintenance, their advantage is that there are no replacement filters required as with mechanical or electrostatically charged filters. Because electronic air cleaners can produce some amount of ozone as a by-product of normal operation, it is important to determine how much ozone different EACs produce. In general, ozone can be minimized with proper maintenance of an EAC, but the amount of ozone generated by an air cleaner can vary greatly between brands and should be a factor when selecting a device for the home.


How well and for how long a panel filter works is a function of the type and density of the media used and the amount of capture surface area that is contained within the filter. To increase surface area, panel filters are pleated like an accordion to get more surface area to capture more particles and last longer. Typically the more pleats in a filter, the better and longer it will work. Also the deeper the filter pleats, 1-inch, 2-inch, 4-inch, the more filter material there is and thus the better and longer a filter will work. It is recommended to replace your air filters every 1-3 months to remove indoor pollutants and create a healthy breathing environment. The amount of filter changes vary with the location and the type of structure, some commercial and industrial buildings require more changes due to high pollutants and occupancy.


To enquire about your air filtration needs or to schedule a commercial, strata or residential HVAC preventative maintenance quote please contact SD ATLAS HVAC at   We are proud to serve Langley, Surrey, White Rock, Vancouver and the rest of the Fraser Valley and lower mainland.



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