Sliding Door: Measure the area you wish to cover. Determine whether you want your door installation to be an inside or outside mount. It is your choice as long as the finished Thermal Shield does not interfere with the door's operation.
French Door: On a French door, shield must be measured as an outside mount with enough clearance to open the door without interfering with the track on either side. Also, there must be enough clearance on top to clear the door frame.