My answer to this question will come shortly, but first let’s consider some issues commonly found in answering this question.
It is often heard that you should not put your piano near a window. This rule of thumb was more true say in 1913 than in 2013. Windows in 1913 did not seal as tightly as modern windows do and homes were much less air tight, particularly around windows. Subsequently, there was more air movement and climate variability nearer the windows than on the inside walls. While the inside wall may still be more stable today, the difference is pretty negligible.
However, sun light, whether it is from 1913 or 2013 is pretty hard on a piano. But in 1913 you were much more likely to have heavy drapes around the windows both to dampen the air movement and block out excess sunlight. Today, we just let the sun pore in, we even will put in sky lights if possible. All of this high powered light will heat your piano, especially the ubiquitous black pianos, causing as much tuning instability as the 1913 walls and windows. Sun light will also fade the color out of any wood finished furniture and flooring.
What about the basement family entertainment area? Modern basements are certainly drier than those found in older homes however by their very nature the humidity levels are higher, sometimes much higher than those found on upper levels of the home. I have a friend who has a newer home and his basement flooded in this spring’s heavy rains. He was able to get his guitars out of his basement, but if his piano has been there he would have lost it. As a general rule I would assume any piano which has been in a basement for more than two years as little to no economic value left. Yes, some will still be fine, but most suffer from mold and animal and insect infestations you can’t see from the outside.
Some modern homes with open floor plans will have large sitting areas on their second floors which make for great, out of the way, places for their pianos. Don’t try to do this on your own! That turn you walk so easily through every day can be nearly impossible for a 500 pound upright to navigate except on its side. Heavy pianos will also destroy those beautiful wood stairs you just had refinished. Let the professionals do it and don’t just go with the cheapest quote, pay the extra for the best movers in town.
OK, so sunlight is bad, windows, as long as they are shut are less bad, and basements are deadly, where can I put my piano?
Where ever you want to! My first rule on piano placement and use is to enjoy it! I can fix everything else. If you like to play by the windows flung wide open in your 100 year old, original condition house, go for it! I personally love to play with the windows open and fresh air flowing all around me. You just may want to tune your piano more often, that is all. If your kids love to jam in the basement with their friends and the pianos gets all moldy, so what! Who would trade that experience for anything?
Put your piano where ever you want and enjoy it for the rest of your life, otherwise why bother.