In general, the springs that are on the door will be what do the lifting of the door, and the opener is in place to assist. We generally recommend at least a 1/2 Horse Power, and this is what most of our professional-grade openers are. If you have an oversized or exceptionally heavy door, you may want to consider a DC motor (not rated by horsepower but often compared to 3/4-1 HP) and consider the drive mechanism as well (chain drive/belt drive).