By Natalie Norwood
Air filters are a hassle; trust me, I get it! They need to be changed every 30-60 days. They come in a variety of styles, sizes, and MERV ratings, which some people can find overwhelming. They aren’t always located in convenient or attractive places either (crawlspaces, I’m looking at you). And of course, you must remember to always have an extra one on hand, so you can actually change it.
At this point you might be wondering why we even bother with these pesky parallelograms comprised of folded paper or cloth in their simple little cardboard frames. Well, as much as we love to hate these guys, they actually serve a very real purpose. Yes, they “filter the air” by trapping dust, some allergens, and potentially even virus molecules and microorganisms, depending on your MERV rating, but they also do so much more than that.
In order for your HVAC system to function properly it must receive the ideal or optimum amount of airflow throughout the indoor and outdoor units. Obviously, if your system is full of dust, pet hair, or other debris the air will face more resistance as that material builds up. Now it’s unlikely you would ever have a line of your ductwork completely closed off due to this debris buildup, but we aren’t as concerned with what’s in the duct (strictly speaking as related with filters). The actual concern is what’s happening to the “guts” of your equipment.
1) Clean filter on left, dirty filter on right
Despite its very simple design on the outside, your HVAC equipment is intricately designed by the laws of physics. Efficiency comes down to minute differences in pressures, air flow (lack of resistance), surface area of heating/cooling surfaces, number of returns/vents, and the size of each line of ductwork. When one of these pieces of the puzzle is off, your system doesn’t perform as effectively as it should. In the long run, this reduces longevity and increases the property owner’s expenses (power use and the cost to maintain/repair the equipment).
2) Hair & debris that was found wrapped in a blower wheel.
When your HVAC equipment is in “cooling” mode, the coils and refrigerant lines inside are actually removing the heat and moisture from the indoor air. The unwanted heat and humidity is then transferred to the outside and “expelled”. The refrigerant contained inside the HVAC system and its intertwined lines, running between the indoor and outdoor units, on a very basic level functions much like the blood in our bodies. It takes the heat from inside the home, outside to the compressor, which increases the pressures in the lines, and pumps it back to the indoor unit, where evaporation occurs as the fan blows over the indoor evaporator coils. The cold air that is produced in the process is then blown into the house providing you with air conditioning. The even more impressive aspect to this process is how the refrigerant changes from a state of liquid to a high-pressure gas while moving from the compressor, condenser coil (outdoor) and evaporator coil (indoor), which is a way more convoluted process than we’ll get into today! In short it produces a continuous cycle of heat and humidity being removed from the indoor air exiting to the outside air, while cool air is being returned inside the home and blown throughout the home.
Now, imagine if all or most of the surface area of the evaporator coil (indoor unit, the one remember, which uses the cold temperatures of the refrigerant inside to blow cold air into the house) is covered in dust and other debris. As more and more debris builds up, the surface of the coil continues to lose its ability to effectively exchange the heat, right? Not only is the overall amount of air flow being reduced, in essence the debris begins to insulate the surface of the coil, preventing the colder temperatures from escaping. Before you know it, you have ice buildup, which eventually leads to a fully frozen coil!
3) Dirt & debris on an evaporator coil (indoor unit).
This can happen on the outdoor unit, just as easily as the indoor.
4) Frozen evaporator coil 5) Ice buildup on outdoor unit (condenser coil).
Key Points to Takeaway:
- Air conditioning is an intricate system designed to remove heat and humidity from the indoor air
- Airflow is KEY to the function of both heating and cooling modes of HVAC.
- Filters do more than keep your ductwork and breathable air clean
- Restricted airflow can lead to a higher incidence of mechanical breakdown due to an increased strain placed on the mechanical parts
- Fan works harder to push air
- Coils cannot release hot temperatures as designed.
- Compressors work harder with increased pressures as the entire system experiences strain and a slowdown with the airflow.
- Your filter could potentially restrict airflow if your MERV rating is too high for the system to handle, but the biggest threat for clogging the system is the dust/debris.
- Dirt, dust, and other debris accumulating on the coils will prevent heat transfer, thus preventing your system from cooling properly. It may also lead to the system freezing – literally
- Filters should be CHANGED EVERY 30-60 DAYS
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