My house is pretty old and unfortunately the ductwork design is in need of improvement. I have a new furnace and air conditioner that do a good job but they're oversized a little and my ductwork isn't ideal. In a few places, one register is split between two rooms with an adjustable damper in the wall. I think I have only two return registers upstairs.
Ideally, how do I want to have this done? My sq footage is a bit under 800 with an unfinished basement. Do I want to have more than 2 return registers upstairs? Do I ideally want one in every room?
I run a dehumidifier in the basement to control the humidity. Would it be better to put a couple supply registers down there to provide some dry cool air in the summer and warm air in the winter? I wonder if putting only returns down there would depressurize the basement and just bring in more unwanted outside air.
I need a lot of help on this if you can tell Thank you very much.
Hard to give any specific ideas about duct design without a site visit, or lots of pictures.
It's always good to have returns to each room (except bathroom, kitchen, laundry, etc), but that can ratchet up the cost of ductwork. Two returns upstairs may be all you need - or you might need more, or perhaps only 1. Impossible to say without some knowledge of your layout.
As to returns in the unfinished basement: Unless you're going to condition that space, then you should not return air from that space. Adding a couple of supply registers won't do you much good either. You should either condition the space or not, but don't do it halfway. Also note that if you plan on doing this, then almost certainly your system would be undersized, so take that into consideration.