Lack of A/C on 2nd floor question

Master Brian

I have an old 1-1/2 story, 1915 Bungalow. At this point, the 2nd floor only has baseboard and space heat and a single window A/C to cool about 600sqft of living space.

The main floor and basement is on my forced air furnace and a/c. I have a door at the top of the stairs on the 2nd floor as well as a door splitting main level from basement.

One question is, since I don't have central a/c on the 2nd floor, is it a bad idea to open windows up there, with the door at top of steps open, while the a/c in the rest of house is running? Since heat rises, would that help with efficiency of my main floor a/c or hinder it? When the door is closed, the stairway traps heat at top of door. I guess I am curious if I'm wasting electricity or actually helping save.

What about the door splitting the basement and the main floor. Once my 15mo old is safe around the stairs, I'd like to eliminate this door as I'm finishing off my basement and don't like the door placement. I understand my cool air will sink to the basement, but if tap into the return air duct in the basement would I help efficiency some? Sometimes that door is open during the day currently and the basement seems to stay a consistent 65* summer, fall, spring and winter. I am finishing it and it's insulated well. Am I wrong to think a return air pulling from this cool air would help keep my house cooler with less usage from the a/c itself? I do realize the a/c pulls humidity out of the house and basements are generally more humid, but not sure of the effect. My basement stays pretty dry, but not sure of humidity level.

beenthere

No, that won't help. it will just let more hot air enter the first floor through the normal cracks and leaks it has.

Master Brian

So, in the end, I'll end up paying more to cool than if I leave the door shut?

Thanks

beenthere

That is what would happen.