How dirty should a filter be when it's changed - I change every 2-3 months?
I use the cheap blue disposable fiberglass filters and there are a few very small dustballs on the filters but otherwise it does not look dirty at all. I switched to the disposable filters because when I used the washable fiberglass or hogshair filters in the past, there was very little dust on those so I thought I wasn't getting enough filtration. But now I wonder if the disposable filters are providing any filtration.
I'm afraid to move up to the pleated filters - I don't see how air moves through those things.