am one of those rare people who actually remember and know when it is time to change the air filter in my central heating and air conditioning system unit.
This is because for starters I have a reminder set on my cell phone to notify me on the day that the time is here to change the air filter of the central heating and air conditioning system.
The other thing is I can tell when the air filter is dirty because my allergies will start acting up. And when this happens even in the slightest, I will change that air filter of my central heating and air conditioning system. It does not matter if it was not the exact time yet, I will change it because it was really needed. This does not happen often this way, but maybe a few times a year. And it is usually when I do not buy HEPA air filters. If I get some air filters that are of the generic brand on sale I usually have to change them a lot sooner than later. This happened just this past month actually. I was using cheap air filters I had picked up on sale at this local dollar store because money was tight. So I could not really afford to get my usual HEPA air filters for my central heating and air conditioning system unit. But money is coming back up for me, so starting next month I will be back to buying the high quality HEPA air filters for my central air conditioning and heating system and no more cheapos for a while.