You should never place a piano in front of an open window. Moisture will attack the strings and cause them to rust. The best location for a piano is up against a wall and as far away from windows and heaters as possible.
According to public health recommendations, a piano can contain biological and chemical hazards. The inside of a piano is filled with dust that contain dangerous, even deadly poisons or diseases. You should never sit in front of a dirty piano.
The Piano Technicians Guild (PTG) has some useful information on piano care. Look in resources. www.ptg.org