As described by the Piano Technicians Guild website: “Relative humidity (RH) is the amount of moisture contained in the air, compared to the maximum amount of moisture that the air is capable of holding”.

As for sound and action, excessive dryness causes the piano's pitch to go flat, while high moisture levels make the pitch go sharp. Also, changes in humidity will make the wooden parts to swell and shrink, affecting tuning stability and touch.

Furthermore, not only the sound is altered, but also the piano itself is harmed: Excessive moisture will swell the wood and rust the strings and all metal parts, while excessive dryness will distort your piano’s soundboard and weaken its glue joints. Repeated changes in the humidity levels will eventually render your piano useless. That is why a precise climate control is so important.

Depending on your needs and possibilities, there are several ways to keep RH under control:

The most effective is the “Climate Control System” which, installed inside the piano, will keep it within the factory suggested limits. This is the most recommended solution because it’s specifically designed for pianos.

The system consists of a series of dehumidifier rods (depending on your instrument and levels of humidity, could be one or more), a humidifier (if needed), and a humidistat (a control unit, which depending on the environment turns on and off the dehumidifier and/or the humidifier).

Degen’s Piano, Inc. is a qualified Dampp-Chaser Piano Life Saver System, installer, and will gladly answer any questions you might have about it.

You may find more on the subject by visiting FAQ section of this site and at the PTG's technical bulletin on humidity control.