How does humidity affect my piano?
    Extreme swings from hot to cold or dry to wet are harmful to your piano. Dryness causes the piano's pitch to go flat; moisture makes it go sharp. Repeated swings in relative humidity can cause soundboards to crack or distort. Extreme dryness also can weaken the glue joints that hold the soundboard and other wood portions of the piano together. Moisture may lead to string rust. A piano functions best under fairly consistent conditions which are neither too wet or dry, optimally at a temperature of 68 degrees F and 42 percent relative humidity.