Herb, I work fo a major filter maker. Micron-Efficiency

9.5 - 50% terrible

17.1 - 75% bad 22.2 - 90% typical of a really cheap filter

33.4 - 98.7% irrelevant

34 - 99% same, irrelevant GM did a wear study in the late 80's, it clearly showed that partic... Login to read more.