I'm not in the HVAC business, but this is how I was able to lower my upstairs heat. I removed it.
My problem, and I suppose yours is similar, I had no upstairs air return. Only air return was downstairs.
Hot air rises, cold air sinks. In my opinion, you can force all the cold air upstairs you want, it's just going to find a way downstairs. The warm air is staying up at the ceiling. That warm air needs to be removed.
Some may disagree with this but it did help my situation. It was a tough job finding a route from the upstairs ceiling back to the return plenum. I used 10" hard pipe, insulated with R8 duct wrap and a 14" x 20" filter grill.
Hope this helps.
My problem, and I suppose yours is similar, I had no upstairs air return. Only air return was downstairs.
Hot air rises, cold air sinks. In my opinion, you can force all the cold air upstairs you want, it's just going to find a way downstairs. The warm air is staying up at the ceiling. That warm air needs to be removed.
Some may disagree with this but it did help my situation. It was a tough job finding a route from the upstairs ceiling back to the return plenum. I used 10" hard pipe, insulated with R8 duct wrap and a 14" x 20" filter grill.
Hope this helps.