I had a local person over to look at my situation, what do you think of what she said?
said that with newer central AC's I shouldn't need to undersize to dehumidify well, she said they are doing the dehumidifying part at the beginning of the cycle so there's more dehumidifying done.
said that a heat pump is no better than just AC for dehumidifying. Somebody told me that a heat pump with heat strips would dehumidify fine at 60F. Apparently they were talking about a situation where you're running AC and using the heat strip so it doesn't ice up. I don't know why having a heat pump would be better than just having AC for that.
But she said that if I got a heat pump, I'd have to replace the furnace, it's an older furnace. It works fine and it's quiet so I don't want to do that.
She said the mini-splits they install don't have ducts, they're just supplying cold air in one place, mounted on a wall somewhere.
She thought that would do fine at air conditioning my 660 sq ft upper floor. I'm skeptical about whether one outlet can dehumidify the whole place, I think you would need air circulating for that. Kitchens and bathrooms often have locally higher humidity.
But she said I would need another mini-split for the 330 sq ft lower floor as well if I wanted to dehumidify there.
But I've read about mini-splits that do have ducts, so maybe one of those could do the upper and lower floors. It would probably be expensive in labor to put in separate ductwork for the AC, though.