Can I convert my standard cold air return duct to a smaller, hopefully, 4" duct? Trying to gain ceiling height in an older basement.
Thanks

NO not really. You need a massive amount of free flowing cold air to return to the unit. 4 inch pipes will not cut it.

Now if you will explain in detail the ceiling layout and post pictures I will try and see if I can see a way for you to do it.

Why do I get the feeling that when people ask questions such as these and do not get the answer that they hoped for they end up ignoring the advice given and do what they want anyway?

Because it is usually true. LOL

Sad. Just plain sad.

I am not trying to single out the OP here either. Just making an observation.