My filter doesn’t look dirty, should I change it?
Changing Air Conditioning Filters
Filtration is a long subject as there are a multitude of filters on the market, literally, “the good, the bad, and the UGLY”.
The best filter is a piece of cardboard; it lets nothing injurious to health through. However, the A/C won’t work with this filtration, so let’s try another approach.
Porosity, it the quantity and size of the “holes” in the filter that allow air passage. A typical flat 2’x2’x1” filter has some 4 square feet of surface area, where the same 5” deep “pleated media” filter contains 78 sq. ft. of surface area. With the greater surface area the size of the “holes” in the filter are smaller allowing it to capture more particles without a high pressure drop which is injurious to system performance and electric consumption.
The size particle a modern filter captures can be quite small, under 1-micron; the head of a pin being 9-microns therefore you may not “see” the dirt however the filter may be almost blocked. The only way to know is to measure the pressure drop across the filter with a Magnehelic Gauge which few homeowners possess. It is good practice to replace small square footage 1” thickness filters, under 5 sq ft, monthly when the system is in full operation (a month such as June) and the deeper “pleated” filters 4” and 5” at the recommended intervals which can be as long as 1-year depending on the conditions in the home. Items such as smoking and quantity of animals in the home effect the air conditioning filter change regimen.
