Good morning! My recent money pit acquisition has a very serious stack problem. It has been 90 degrees on the second floor and probably 65 on the ground floor. I am going to do my best to try to ‘plug leaks’ however I expect that it’s going to be futile. 
Is there a way to ‘move’ the air around the house to put some of this stack effect to use?

Also, basement floor radiant heat instead of putting a minisplit down there- would that be worth it? It’s never hot down there but I expect that once I pull up that super cushy carpet and leave it concrete it’s going to be frigid. 
Radiant heat on basement minisplits first and second?

Thanks!