and to further that, the more sugars there are to ferment, the more activity there will be, the more heat is created. so you're aiming for 68-72 as the beer temp, not the ambient air temp. one way you can easily help lower this if it's not possible to lower the ambient temp is by putting it in some kind of tub filled with water. if even the water is 66, that will be better than ambient air at 66. and then you could even add a bit of ice, or point a fan at the water with a wet towel draped over the top of the fermenter, and that will significantly help keep those temps low. after the main activity has stopped (anywhere between 4-7 days), then you can start to allow the temp to rise up into the 70s.