I never realized how helpful air filters were as a landlord… Sure, as a landlord, I really understood why air filters were important for an HVAC unit! When you own several houses in a city, you swiftly begin to realize that when you do not change the air filter in your HVAC unit, you are really going to start experiencing problems with your HVAC units, then the air filter prevents dust from coating all of the parts within your HVAC unit, and if you change your air filter, you will find that your HVAC equipment absolutely breaks down less often than if you ignore the air filter in an apartment; Also, by increasing the air filter when you are supposed to, you can help your occupants to not get sick as often, then by forgetting to change the air filter, you are forcing your occupants to breathe in nasty air, however, now that I have been a landlord for a long time, I have discovered that the air filter can do something even more useful; In our house, I have a policy that states that you cannot smoke inside. However, I can tell that people smoke inside, and first of all, the aroma gives it away, but since people will claim that it is because of their clothing, I cannot use that to prove the smoke. However, by increasing the air filter in the HVAC equipment properly, I can tell if they smoke inside. When you smoke inside, it changes the color of the air filter in your HVAC unit, but people that smoke physical cigarettes turn the air filters orange, and people that vape turn the air filters black. This is a sure way to see if someone is smoking. Who knew that air filters could be so helpful?