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Some filters do have a spray on them.

Originally Posted by Birmingham

depends on the style of filter and the merv rating.

-fiberglass throwaway filters some it doesn't matter some are sprayed with a type of spray adhesive that really doesn't ever dry you want the sticky side to be up stream so it can catch the smaller particulates and hold them to it with the air pressure.

-paper style throwaway filters its normally just the wire support so the filter wont be sucked into the return, i have made a dollar or two on service calls where i pulled a filter out of a blower wheel.

-higher efficiency media can be mechanically or electrically charged HEPA they will only work in one direction and normally can not physically be installed in the wrong way, the frames are made not to fit.

Thanks for the info. I thought i had heard that one style has something sprayed on them to catch particles.

depends on the style of filter and the merv rating.

-fiberglass throwaway filters some it doesn't matter some are sprayed with a type of spray adhesive that really doesn't ever dry you want the sticky side to be up stream so it can catch the smaller particulates and hold them to it with the air pressure.

-paper style throwaway filters its normally just the wire support so the filter wont be sucked into the return, i have made a dollar or two on service calls where i pulled a filter out of a blower wheel.

-higher efficiency media can be mechanically or electrically charged HEPA they will only work in one direction and normally can not physically be installed in the wrong way, the frames are made not to fit.

Basic pleated filter
Use this arrow for the support on top
If installed the wrong way, the support won't be there
When filter is loaded with dirt
Air will suck up the filter Media out of cardboard frame.

I believe some filters have increasingly denser filtration media that is designed to catch the big stuff first and the smaller stuff as the air makes its way through. Also, if a person takes the filter out, it serves as a reminder of which way the filter was in so you don't suck all the dirt off by putting it in backwards.

Filter ?'s

Why exactly do air filter have a specific air flow direction arrows besides the fact of that ones that side has supports? I was told that one side has something on it that helps capture particals. Is this true?