If you open all the doors in a house (except doors to outside, obviously) and turn the AC on to cool the entire house, will the floor above the AC get cooler or hotter?
I can't imagine it would have much effect on the floors above either way. Probably cooler, but I could be totally wrong.
It's weird because when I walk between floors the difference is immediate, I am not even halfway down the stairs and suddenly it's much cooler. I have to wonder if the AC is simply useless for cooling above floors, or, it's actually making above floors hotter. But I need to know.
edit: For the record I am only talking about 1 floor above. So basically 2 floors are involved. (the floor with the AC, and the floor above) Edited the original post to reflect that. (i.e. I replaced the words "floors above" with "floor above")
Do you only have a single AC? Man, must suck to live in places that don't normally get hot.
All I have to offer to the conversation is that warm air rises, but I'm not sure exactly how an AC cools, so I can't answer your science question with enough confidence.
But unless you have a very very strong AC with massive capacity and a tiny house and the cooling required (temp difference to outside + insulation factor) is small, the top rooms are unlikely to notice any appreciable difference. So in most cases it won't do jack shit for upper floors.
Well generally speaking, heat rises. So yeah, the second floor would probably stay fairly hot. I mean with natural airflow throughout the house i'd imagine it'll eventually get cooler upstairs but it'll take awhile.
If a second AC unit isn't possible at the moment, maybe putting it upstairs might be the best bet.
It won't make the 2nd floor hotter, but it probably won't cool it much either.
The 2nd floor is always going to be hotter because the sun is heating up your roof and turning the attic into an oven, unless you have some extremely good attic insulation and venting, the top floors of the house will be greatly affected by that heat.
@kidavenger: Well, and by natural convection - the warm air wants to rise (less dense) and the cool air wants to sink (more dense), so without some sort of 'active' (read: fan) way of moving the cold air up, chances are the second story won't get cool.
As to the ways ACs work - it's just a 'heat mover'. Since we all know energy (in this case, heat) can neither be created nor destroyed (with few exceptions and certainly not under living room conditions..), an AC unit simply moves the heat outside (via the coolant), bleeds it off into the atmosphere, then grabs more and repeats the process.
Here's the trick to 2 story homes with 1 AC unit: You have to set the thermostat (assuming it is downstairs) cooler than normal in order to try and get the upstairs at the level you need. Of course this will just cause the downstairs to be colder than you would probably like and the AC unit may or may not be able to keep up.
Like other people have mentioned, heat rises. The temperature near the thermostat is what you wanted so it shuts off. Now there's nothing but heat starting to build up top until the next time the thermostat kicks in because the downstairs got warm enough. The floors will have the same temperature in the summertime so you have to compensate somehow.
Personally, I just recommend getting a good standing fan and pointing it at you. That right there will fee like a 5 degree difference. I bought this from Lowe's and helped a lot when during that last heat wave we had of 110º for a week and a half.
I think it is less the power of the AC and more the power of the fans. Very little of that air upstairs is going to flow down to be replaced by cooler air. Maybe if you had fans upstairs circulating the air down the stairs.
The AC itself isn't going to make the up stairs hotter. Might not make it cooler though.