The environment in which you place a piano is very important. Remember this is a wooden instrument with thousands of parts essentially hiding inside a piece of furniture.  Extreme humidity changes can affect the moisture content of the wooden parts causing them to swell or shrink. This may also cause the finish to crack and chip, the string tension to change so as that the piano requires more frequent tuning and the critical tolerance of action parts to be distorted or possibly the soundboard to crack. 

Generally an atmosphere that is not comfortable for people is not very good for pianos either. 

Therefore it is best to keep sudden changes of temperature and relative humidity to a minimum. Avoiding temperatures above 90 and below 60 and relative humidity below 40% or above 60% will help provide the proper atmosphere for your piano. 

And at all costs avoid placing your piano near any heating source or steam radiator. It is also advisable to keep your piano away from direct sunlight in order to better maintain the finish. Every piano should be tuned at least four times the first year if new and twice a year thereafter. This is not only better for your ears but also for the longevity of the instrument itself.