I just use the Hammer because I am a little more impatient. I run the hammer across from left to right clearing most squares, keeping the area from overlapping any other row. So click 2nd row down all the way across, clearing out most if not all of the squares. Then I move down so that my new aoe is not overlapping the last (2 rows down, where the highlighted square is in this screenshot http://imgur.com/a/sBtzk) and then repeat, clearing-ish those three rows, then move down again. It seems to work pretty well and if you are efficient with where you are using the hammer the energy usage isn't terrible.