Your piano is made primarily of wood. When the moisture content of the air around the wooden parts is high, natural law dictates that the parts absorb the moisture as they seek equilibrium. In the same respect, when the relative humidity of the air in and around the piano drops, the wood releases the moisture back into the air. Wood expands as moisture is introduced and contracts as moisture is removed. This causes several detrimental effects in your piano:
The action parts - Just as wooden doors and drawers become tight and may even stick in times of high humidity, the thousands of action parts in your piano also expand causing an increase in friction that can at the least causes excessive wear and may cause notes not to sound altogether. In addition to the decline in response to your touch, swings in humidity put a strain on the glue joints that keep the parts together. In Southeast Georgia, high humidity is a fact of life. The wood in your piano however, has put off the things of old such as sprouting leaves and is best preserved when moisture is kept under control.
A piano is a significant investment worth protecting. We have briefly mentioned a few vital areas that can easily be protected from excessive moisture and humidity changes. Humidity Control Systems are affordable, silent, cost but pennies a day to operate and are maintenance free. Our systems are guaranteed for five years when installed by a qualified piano technician and our experience has been they work flawlessly long beyond that period - just keep them plugged into the outlet and the Humidity Control System does the rest. We've included a link below so you can view the manufacturer's web site. Since relative humidity here along the coast rarely drops to a dangerous low for a piano (and even then not for a significant amount of time for the piano to be adversely affected) we normally install systems that do not include a humidifier. So here's to piano longevity, tuning stability and preventive maintenance!