Humidity and Tuning Stability
The big factor in tuning stability is the changes in pitch due to the rise and fall of relative humidity. These can be both large seasonal swings as well as the AC and heat turning on and off during the day.
Many people have the wrong idea that using central air conditioning keeps humidity down. While it does have some effect, the piano, which is mostly wood, still takes on a lot of moisture throughout the summer and fall. The soundboard and case expands. Usually the tenor and treble become sharp. The bass section may not move as much which results in wild octaves between the 2 sections.
Often in the fall I’ll find the pianos ¼ of a half step sharp in the middle. Then the opposite happens when the heat comes on which blows hot and very dry air. The soundboard shrinks and the piano can drop in pitch quite a bit.
The constant expansion and contraction of the wood causes cracking and splitting in the soundboard and bridges over time. It also causes wood cells to crush causing loss of resonance and crown over time.
Custom string cover with support sticks sewn in.
Installing a Damppchaser System
I strongly recommend Installing a Damppchaser system in your piano.
With the Humidistat Control it both adds and removes moisture as needed. The system installs under the soundboard in grands and inside the case in verticals and creates a separate environment from the room. With this system not only is the piano protected but tunings will last much longer.
Contact me to install a system in your piano.
Other Recommendations
Covers
I also recommend in many cases a custom string cover in a grand or a back cover on an upright. These make the Damppchaser work more effectively.
Deflect Airflow
Another factor in tuning stability is air vents blowing directly onto a soundboard. It is important to deflect airflow away from the instrument.
Avoid Direct Sunlight
Protect the piano from hot direct sunlight. Sunlight will also fade and peel the finish.