HOW OFTEN SHOULD A PIANO BE TUNED?
This is the most frequently asked question of all. The best answer is what the manufacturers of Pianos themselves say about it. New pianos should be tuned four times a year for the first three years. After that, once or twice a year.
The good news is, Pianos which have been neglected can be restored by regular servicing (esp. tuning) and it will render them a more reliable instrument.
ONCE A YEAR is the minimal manufacturer/ factory recognized standard for frequency of tuning a piano. The instrument is made predominantly of two materials, steel and wood. Wooden sounding boards, etc. are very sensitive to humidity changes. Unfortunately, the moisture content of the soundboard changes 24-7 throughout the year and has it's effect changing the instrument's string tension (tuning) regardless.
Annual tuning keeps the Piano near it's intended A-440 Pitch/Frequency and cannot harm the instrument. Only if you have your instrument serviced regularly, will it keep its high quality. The convex/concave shape of the spruce soundboard was design-engineered & manufactured for the constant string tension of A-440 pitch. When the pitch falls considerably, the dimensional shape of the soundboard changes somewhat. Whether this becomes permanent or not, it lessens the tone quality and sound volume of the instrument from that which it is capable of.
David Henson
Certified Piano Technician