1. Built-In Filter Change Indicator
You may have a thermostat that has an indicator to remind you to change your air conditioner filter at predetermined times. Some can even be programmed to remind you at an interval of your choice. While these are good for reminders, they not too valuable because they don’t specify when your filter has actually become clogged enough to stop air flow and start ruining your unit’s operation.
2. Monthly Check Ups
Every month, take your filter out and inspect it. When you see that it’s dirty enough to actually change, it’s a good idea to write the date down on the side of your duct system, air handler, (or whereever your filter is installed). After a solid year of doing this, you’ll have a good guide to follow for when you have to change your AC filter.
3. Purchase An Air Filter Gage
The best thing to do is to use an air filter change indicator. These inexpensive devices mount onto the side of your air handler and, as your filter becomes dirty, an indicator needle moves from “Filter Is Clean” to “Change Filter”. They’re accurate because they work on negative air pressure, as opposed to you trying guess.