I have only installed 1 heat/cold vent in my HT room. th room is 15X25 and I have included a diagram to show where the vent is. I need to know if you guys think I should add one more and if so would it Be OK on the same wall? Also should the return go near the floor or ceiling? I have the heat/cold vent a few inches off the riser in the rear of the room. any thoughts would be great. the red spot is the heat/cold vent I have so far.