The amount of water in your home's wood varies greatly depending on the relative humidity (RH) level of your indoor air. If RH is too low, your indoor air will absorb water from the wood, causing it to shrink. If RH is too high, the wood will take on moisture, causing it to swell.
This is why maintaining optimum RH levels is important. Industry experts recommend keeping your home's relative humidity levels between 30-60% for musical instrument preservation.
Too much humidity in your home can cause:
Too little humidity in your home can cause:
"Seasonal and even daily changes in humidity cause wood parts to swell and shrink, affecting tuning stability and touch. Extreme swings in humidity can eventually cause wood to crack and glue joints to fail...Maintaining the correct environment will preserve your piano investment for a lifetime of enjoyment." - Piano Technicians Guild