Common lore says that a piano should always be on an inside wall. This is not necessarily true. Evenness of humidity and temperature is what you should strive for. Thus, a piano in an unheated room is better off than one in a family room that's alternately heated, cooled and ventilated with open windows. If the piano is facing a fireplace or heater and its surface feels warm, it's too close.
Consistency is more important than the actual levels of temperature or relative humidity.
If you can't find a suitable location, have a climate control system installed in the instrument itself. These units can greatly improve tuning stability and other climate-related problems where it's not practical to control the environment of the entire house.