I do believe it is a "stinking" ship. If it is ok with you, could you help me with one last question and I'll be out of your "air" for the evening...

I was told that my house does not have a return air duct.
It doesn't surprise me to hear this since not much about this home appears to be done properly. Could you explain the benefits of the return air duct particularly since I will be considering the new Rheem furnace? I am not HVAC saavy so I do not know what impact no return air has had/will have... Thx, much.