Pianos are Sensitive!: Pianos are sensitive to changes in temperature and humidity.  Where you place the piano is critical to the stability and longevity of the instrument. 

Pianos Don't Like Change: As far as possible, the piano should be in a place with the least amount of change in the atmosphere, out of direct sunlight.  That means as far from a heat source, vent, or open window or door. 

Sunlight: West facing windows allow a lot of heat in, which is not good for a piano.  Some brief sunlight from a southern sky or eastern window is okay.  Wood colored finishes are especially prone to bleaching in sunlight, even if it is indirect.  I strongly advise getting UV film on your windows to protect the finish of your piano and furniture.