When was the last time you changed your return filter at home? You know, the one you forget about until it's too late: your system quits working, you call the AC tech out to your home and you quickly change your filter so that you don't look like a scrub. And by that point you could plant potatoes in the dirt accumulated on the face of your filter.
Your return filter is the one protective measure for your HVAC system that you control. Let's look at why the return filter is needed and what it affects:
First and foremost your filter is designed to protect your indoor cooling coil, known as an evaporator coil, from collecting dirt and becoming clogged. Your evaporator coil resembles your car radiator coil, being a circuit of copper tubing surrounded by tightly-spaced aluminum fins. If dirt and dust get trapped between those fins air cannot flow across the coil, and that's what we scientifically refer to as bad. Soon your refrigerant pressures drop, the coil temperature dip below 32 degrees F. and the condensed water vapor begins to freeze to the coil. Soon you have a large block of ice, which restricts airflow even more, effectively compounding the problem. You may have seen this in the form of ice on the large refrigerant line leading up to your outdoor unit, which means your indoor coil is an igloo. This phenomenon occurs anytime your airflow is reduced while the AC unit is running. So a dirty filter restricts airflow, the indoor fan will begin to pull the dirt through the filter to the evaporator coil and soon your coil is plugged with dirt, which brings us neatly to the next point.
In addition to removing heat from the air, the evaporator coil removes humidity. Warm moist air will condense back into water when it moves across a cold surface, which is why your beer bottle sweats on a summer day. Your evaporator coil is slanted or angled to allow this condensation to run into a drain pan, where it can then run through a drain line to the outside of your home. But what happens when this water hits the dirt that has collected on your coil? That's right, it becomes mud, which then clogs your drain line and causes the condensation to overflow the pan and drip into the emergency drain pan that your furnace or air-handler sits in. And since most of the emergency pan drain lines aren't graded well, the pan overflows and you get a nice water-spot on the ceiling. So a dirty filter encourages a dirty coil, which equals a clogged drain and water-leakage.
A blocked filter will also reduce your AC system's efficiency, or how much bang you're getting for your buck. As I mentioned above, a reduction in airflow across your evaporator coil will change your refrigerant pressures, meaning the system will not work as it was designed to. A reduction in airflow also means you aren't removing the proper amount of humidity from the air. Excessive humidity is actually the first thing your AC system has to overcome before any sensible cooling can occur. If the air in the living space cannot be fully processed, or conditioned, it will retain humidity and feel stuffy, or muggy. Your system will run longer as a result, which equals more money spent on your electric bill. So a dirty filter equals more humidity and a reduction in efficiency, meaning more dollars for less results.
Finally, what about your indoor air quality? Is your home excessively dusty? Most of the visible dirt and debris that collects on your filter (and your counter tops, for that matter) is actually exfoliated skin. Gross. Think about that the next time you let a filter go for six months before changing it. Your filter is operating at less than 100% from the first moment it begins to collect debris, so what about a week from that? A month from that? Most filter manufacturers and HVAC experts recommend that you replace your return filter at least every thirty days. And when you replace that filter think about all the particulates that probably aren't getting caught, that just continue to circulate in your air stream. A good quality filter will not only protect your evaporator coil, it will help clean up the breathable air in your home. On most commercial buildings, outside air is brought in to mix with the building air in what is known as a fresh air exchange. More than likely your home only circulates the same air over and over again, with very little fresh air infiltration. The cleanliness of this air, therefore, is paramount. And is directly related to the effectiveness of your return filter.
