Good morning, yes, you can leave it externally, this is how this work is done, in terms of length, that depends, if it has all the condenser inside the cabinet and leaks, it is necessary to place an external grill of approximately 11 to 12 cubits for being a 1/4 hp engine, but if it is only the section that travels internally through the frame of the doors, you can place about 3 meters of 1/4 in. Pipe, or a small external grill of approximately 5 elbows.