AC Air Filters

AC air filters have a rating, not always easy to find, but they have one.  The most common is the MERV rating, explained below:

MERV Rating (Minimum Efficiency Reporting Value): As you have already learned, the MERV Rating is the primary rating system used in the industry, both domestically and internationally. Established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, MERV rates a filter’s ability to capture and hold particles and pollutants.

MPR (Micro-Particle Performance Rating): MPR Rating is a rating system developed by 3M. It rates the manufacturer’s filters and their ability to capture airborne particles smaller than 1 micron.

FPR (Filter Performance Rating): FPR Rating is a rating system developed by The Home Depot for brands sold through their stores, including Honeywell. It utilizes a color code and number scale (4 to 10) that closely resembles the MERV rating.

AC filters are a trade-off between efficiency and air flow.  You need air flow to cool your home.  The more air you move, the more times you change over the air, the more cool air you are circulating, the cooler your house stays.  The filter’s efficiency reduces the air flow, but means the filter traps finer particles in the air. Taken to extremes, to maximize air flow, you’d use no filter. This will work for a short time and is the most expensive solution (it cost $$$ to get the AC evaporator coil cleaned ). The opposite end is to put a piece of plywood in the air filter slot.  No dust gets through the system, but no air does either.

In Florida, in my opinion, the MERV 8 filter is the best bet for use.  We’re talking the $6 to $10 pleated paper filters.  The $2 fiberglass filters do not filter enough and you’ll end up spending more money to get the evaporator coil cleaned, the AC services and have dusty ducts.  The $20 allergy rated filters are too fine. The plug up in about a week’s use and reduce the air flow.  They have to be changed out much more often.

Here’s an evaporator coil that is in serious need of a good cleaning.


In addition, change your filter monthly.  Do not believe the 90 day claim on some filters.  This is Central Florida.  We are in a sub-tropical climate, meaning we have more dust, mold and pollen in our air than most places.

After you’ve changed the air filter, find the drain line access:

ac drain line

Pull the cap off and pour approximately 2 cups of white vinegar down the drain line. This will flush the system, and prevent the growth of algae and slime in the drain line.

ac vinegar

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