Window AC vs Central AC

Check these articles.

Window ACs are MORE energy efficient than central ACs, NOT including installation and maintenance.

To replace a central AC would be about $3000 for the unit and a $1000 labor, For that you can buy 10 equivalent window ACs.

The price of a maintenance call on a central unit will buy a good window unit.

http://theenergynerd.blogspot.com/2011/05/fascinating-world-of-air-conditioner.html

http://www.greenbuildingadvisor.com/blogs/dept/musings/window-mounted-air-conditioners-save-energy