I am going to have 4 heavy-breed hens in a coop that is probably about 5' x 3.5' x 2.5' tall (with a /\\ shaped roof so that adds a little extra space), with at least 1 window. The run is going to be underneath (with an added tractor attached at times and free ranging each day for a while). I live in New England with sometimes brutally cold winters and hot humid summers. Is there a minimum amount of vented space I should plan into my coop-building plans? I assume I'll have triangular shaped vents at the top of the sides, under the roof. How man square inches of vent should I have and where should I put the vents so that the chickens get plenty of ventilation but no drafts/draughts? I thought I read there was a formula somewhere for this.