You shouldn't have any trouble with maintaining your temp. We have 56 apartments at work that each use one. The units are installed in the living rooms and even in the apartments with seperate bedrooms it will still maintain both areas. I don't remember the exact footages of the apartments but we are only running 12,000 btu units. They work excellent all year long in northwest PA. In the summer you want to keep an eye on the drain. They tend to get gunked up with dust and dirt after awhile and will leak inside, that's even with ours pitched out.