I sort of started this thread elsewhere, but very poorly.
I have a Bryant Evolution A/C system, ductwork in my attic. reasonably sized ducts (8" feeds of 12x30 mains). system is a year old, ductwork is older. For yuks last night I checked the static pressure at the stat with the fan on high, and read 1.37!!! Then I thought - end of season - dirty filter! So I went up to the attic. With the filter slid out most of the way (so it's still blocking the opening in the side of the ductwork, but NOT the airflow), my static dropped to 0.8. So I sighed relief. Then I changed the filter and put it back, and the SP went back up to 1.34???
It's a Spacegard (Aprilaire) 2200 Media filter.
Does this make sense to anyone? It doesn't to me. Should I get a different filter? Should I stop checking my static?