A few years ago, we added an external glass door to our south-facing front door. Don’t do this. The glass helps trap heat and turns the whole thing into an oven. It gets hot enough to burn you and has damaged the paint on the front door. As the energy.gov site says, “Never add a glass storm door if the exterior door gets more than a few hours of direct sun each day. The glass will trap heat against the entry door and could damage it.” Would have been nice to read that a few years ago.