Do you go by the calendar or by how gross the filter looks when you pull it?

I check mine every month now, and I don't even go by the calendar anymore. I pull it out and hold it up to a lamp in the hallway. If I can't see light coming through evenly, it goes in the trash, end of story. The 90 day printing on the frame means nothing in a humid place where the blower runs half the day.

I'm up near the coast in South Carolina, so not quite as brutal as the Keys, but close enugh. I used to buy the cheap fiberglass ones and swap them monthly, then I switched to a pleated one rated around MERV 8 and found it loaded up just as fast but caught way more. Now I buy a four pack at the start of summer and just plan on going through them.

One thing that helped me was writing the install date on the filter frame itself with a Sharpie. Sounds obvious but I went years guessing wheather it was two months old or five. Now my wife and I both know at a glance, and whoever walks past the closet first does the swap.

Also worth checking whether your return path is pulling in attic or wall cavity air, becuase a leaky return will choke a filter fast no matter how often you change it.

I went a diffrent direction with this problem a couple years back. Instead of trying to stretch a nicer filter and judging it by looks, I just stopped buying the pricey pleated ones and buy the basic MERV 8s in a bulk pack from the hardware store, then swap every single month no matter what they look like. Costs me about the same over a year as replacing the fancy ones every 90 days, maybe less.

The way I see it, a filter that's half loaded restricts airflow, and restricted airflow makes the blower work harder and the coil run colder in a humid place, which is exactly what you don't want. My upstairs unit in coastal Georgia iced over one August because I'd let a pleated filter go too long, and the repair visit cost more than five years of cheap filters. The lamp trick the earlier poster described is fine, but honestly by the time a filter fails that test it's been choking your system for a while alredy. Monthly swaps on the cheap ones mean I never have to think about it. I put a recurring reminder on my phone for the first of the month, swap it while the coffee's brewing, done. My filter slot is in the hallway ceiling so the whole job takes two minutes on a step stool.

Run time matters more than the calendar anywhere the AC barely shuts off from May through October, and from the sound of it your unit qualifies.

I just learned the arrow on the frame actualy matters and points toward the machine, not the room. I had mine backwards for who knows how long til a neighbor looked at it for me. No wonder it always seemed clogged on the wrong side.

Also my dog sheds like crazy in spring and the thing fills up way faster then, so maybe pets make a difference too? Does hair really get pulled into that spot or is it mostly just dust?

I do tune-ups on the side and the worst one I saw last summer was exactly this. Homeowner went five months on one filter, blower was starving, coil iced over and he thought he had a refrigerant leak. Cleaned the filter slot, hosed off the coil, and the temp drop across the coil went from about 9 degrees back up to 18. Filter was the whole problem. Down there in that salt air you're smart to pull it early, the humidity alone loads them up.

First post here, hope this is the right thread. We rent a small duplex and until last month I honestly did not know the filter was my job. Landlord mentioned it in passing and I found the slot behind the couch of all places. Mine is a wall return, not a closet like you all are describing, and it seems to get dirty way faster than I expected even though our unit is tiny. I set a reminder on my phone for every 30 days as a starting point since I have no feel for it yet. Is a wall return worse for pulling in dust from the room or is it basically the same thing?