How did you come up with these calculations? I thought it was something like 2 CFM per square inch on the duct size? I know the supply trunks(2) off the furnace are a combined 32 x 8. Both taper down along there runs. Returb is 26 x 8 the whole way until it enters furnace( gets larger) Not sure if this helps. They have another day left here, so I want to make sure anythingthat needs to be done is done. Thanks again for all the help.
If the return duct is large enough, could I simply put another return opening on the other side of the wall? It would be aesthetically neutral. If so, how large?