Hi Ann. How high is your ceiling?
Floor area (3000 sq feet) times height equals volume, so if you have 8 ft rooms, then you have 24000 cubic feet. If your rooms average 7 ft, you have 21000 cubic feet and so on.
Divide the volume of your house by 6000 and you get the number of foggers you will need.
Hope this helps,
Stephen La Rocque.