We are intending to remodel our kitchen on the first floor of our home. Some of the air conditioning and heating ducts (approx. 9" high by 12" wide) run on one side near the ceiling of the kitchen and we would like to make them smaller by using flat ducts, (about 3" high) so that we can increase our cabinet space. One contractor said that it was possible to do this and another contractor said no since you won't have enough volume of air going through them to heat/cool the second floor. Who is right? Please advise us. Thank you.