I forgot to mention anywhere that after I had had my attic fan, roof fan, for about 15 years, I was up on a ladder and found a layer of lint or something over the entire soffit vent. It was like the lint one takes off the lint trap in a clothes dryer, though not as heavy as it gets in my drier. I have a two story townhouse and couldn't see it from the ground, even when I knew it was there.
My soffit vents are about 4 inches deep, front and back of the house and as wide as the house is wide, covered with something like window screen.
Smaller soffit vents would get an even thicker level of "lint".
Meirman
If emailing, please let me know whether or not you are posting the same letter.
Change domain to erols.com, if necessary.