Qdeathstar:
Right now, the stepper turns a lever that rotates a 1ft aluminum bar.
That is not clear.
In general, torque equals distance times force, provided that the force is perpendicular to the distance.
The torque reqd to hold a door open can be measured by attaching a fish scale to the knob (holding the scale perp to the plane of the door) and multiplying the force times the width of the door (to the knob).
You'll need more torque than that to overcome friction, the inertia of the door, wind pressure, stack effect, and aerodynamic effects.
You can estimate the reqd total torque by pulling the door open with the scale, at the speed you want the door to open. Then double it.