Humidity Control

By far, the biggest factor affecting tuning stability is humidity; more precisely, fluctuations in humidity.

The more stable the humidity, the more stable the tuning. Let’s look at two examples:

1) A piano is tuned in the winter, say, December. At this time the humidity is low at 30% and it stays fairly close to this level until March. So far so good…the pitch is staying fairly constant as well as the tuning.

Then March arrives and the humidity increases to 60%. What happens? The pitch of the piano also goes up. It is now sharp and out of tune.

2) A piano is tuned in July when the humidity is high at 70%. The tuning remains relatively stable until December when the humidity falls to 30%. What happens to the tuning? It’s now flat and out of tune. 

What’s going on? In a nutshell: the soundboard is reacting to the humidity. 

The strings of a piano are tightly strung across the soundboard. The soundboard is a thin, but very large piece of wood (usually spruce) that acts as a speaker to increase the volume of the strings.They don’t actually touch the soundboard, but run across long wooden “bridges” that are glued to the soundboard.  

Being made of wood, the soundboard is very sensitive to changes in humidity. So, in example one, the humidity hovered around 30% for several months and the tuning remained stable. Then the humidity increased to 60% when spring came and the soundboard absorbed this extra moisture which causes it to swell. While it is expanding it is also pushing upward on the bridges and since the strings are attached to the bridges they also are pushed upward. 

And when the strings are pushed upward they get tighter and tighter which means their pitch also goes up. Which means the piano has now gone out of tune. (The reverse happens in example two.)

Controlling Humidity

There are several ways to control humidity, although most of them are very expensive or unworkable. If the humidity where you live fluctuates wildly from season to season, the best way to make piano tunings more stable is to either have your piano tuned more often (2-4 times per year) or have a humidity control system installed directly in the piano.

This system is known as the Piano Life Saver System (also called a Dampp-Chaser) and can be very effective in controlling humidity in a piano year round.

For more information on this system just click on the link below:

As a certified installer of this system, I would be happy to answer any questions you might have. Just give me a call or send me an email: Contact


© Gregory Griggs 2021