A compilation from the Piano Technicians Guild and other sources
Your piano is made primarily of wood, a versatile and beautiful material ideal for piano construction. However, being
made of wood, your piano is greatly affected by humidity. Seasonal and even daily changes in humidity cause wood
parts to swell and shrink, affecting tuning stability and touch. Extreme swings in humidity can eventually cause wood
to crack and glue joints to fail.

Other materials in your piano also are affected by changes in moisture content in the air. The many felt and leather
parts in your piano's action can change dimension, affecting regulation and friction, or stiffness of the touch. Very
high humidity can even create condensation on metal parts such as strings, tuning pins and hardware, eventually
causing them to rust.

How does humidity level affect my piano's tuning?

Swelling and shrinking of the piano's soundboard is the most immediate and noticeable effect of humidity change.
The soundboard, a sheet of wood approximately 3/8 of an inch thick, is made with a slightly crowned shape. The
strings pass over the soundboard and are connected to it by a wooden piece called a bridge. The upward crown of
the soundboard presses the bridge tightly against the strings.

As the moisture level in the soundboard increases during periods of high relative humidity, the crown expands and
pushes the bridge harder against the strings. The strings are stretched tighter and the piano's pitch rises. Because
this increase in crown is greater in the center of the soundboard than at the edges, the pitch rises more in the
middle octaves than in the bass or treble registers.

During periods of low relative humidity the soundboard shrinks, reducing the crown and decreasing pressure against
the strings. The pitch drops, again with the greatest effect noticeable in the center of the keyboard. When relative
humidity returns to its previous level, the average pitch of all the strings will return to normal, although the exact
pitch of individual strings will be slightly changed from their original settings. Thus, a piano only will stay in tune as
long as the relative humidity level in the air surrounding the soundboard remains constant. Extreme humidity
changes require making greater changes in string tension to bring the piano into tune. This upsets the equilibrium
between the string tension and the piano frame, and the piano never becomes stable.

What is relative humidity?

Wood swells and shrinks in response to changes in the relative humidity of the air around it. 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. The moisture content of air is affected by weather as well as conditions and activities within the home,
while the moisture- holding capacity of air varies with temperature. One way of thinking about RH is that it is a
measure of air's tendency to absorb or release moisture to its surroundings. Thus when the RH of air in a room
increases, moisture will tend to transfer from the air to wood and other absorbent materials in the room. When the
RH of air decreases, moisture will transfer from other materials back into the air. The RH of the atmosphere is always
changing by the hour, and more dramatically, with the seasons. Consequently, the wood and felt parts in your piano
are constantly changing dimension as they absorb and release moisture.

Since RH depends upon the temperature and moisture content of the air, it is not possible to maintain a constant RH
by controlling room temperature alone. In fact, maintaining an even temperature while moisture content varies will
cause RH to change.

What can be done to minimize humidity problems?

Keeping the humidity level around your piano as constant as possible will help it stay in tune longer as well as slow
such damage as soundboard cracks, loose tuning pins, and glue joint failures. The first and simplest precaution you
can take is to position your piano away from areas where it would be exposed to extremes of temperature and
humidity such as heating and cooling vents, stoves, doors and windows. Direct sunlight is especially damaging. If
your home is not well insulated, an interior wall is preferable to an outside wall.

Controlling the humidity within the home is another step you can take to preserve your instrument. In most areas of
the country the relative humidity is very low during the cold winter season, and very high during the spring and
summer. In other areas these humidity cycles are reversed. Wherever you live, you have probably noticed the
symptoms of low RH (shocks from static electricity when sliding out of a car or after walking across carpet), and the
signs of high RH (limp, soggy feeling newspapers and sticking doors). To monitor RH changes in your home, you
may wish to purchase a moderately priced wall hygrometer available from most instrument supply companies or
electronics stores.

Use of a room humidifier during dry seasons will help somewhat. However, too much moisture added to a room
during winter months can cause condensation to form on cold surfaces such as windows, eventually causing mildew,
rot, and in extreme cases, damage to the building structure. During the humid season de- humidification is needed.
If your humid season is winter, keeping the home evenly heated will help. However, humid summer situations require
much more elaborate de- humidification systems. Unfortunately, it is seldom possible to adequately control the
relative humidity of a piano by controlling the room environment alone.

A very practical and effective answer to humidity problems is to have a humidity control system installed in the piano
itself. These systems consist of three parts: a humidifier for adding moisture to the air, a dehumidifier for eliminating
excess moisture, and a humidistat or control unit which senses the RH of the air within the piano and activates the
system to add or remove moisture as needed. These systems are designed to maintain the RH of the air within the
piano at the ideal level of 42%. The components are installed out of sight, inside the case of a vertical piano or
under the soundboard of a grand. They are easy to maintain, and can be installed by your piano technician.

How will humidity control benefit my piano?

While not eliminating the need for regular piano maintenance, humidity control will allow more stable tunings by
reducing the radical pitch changes your piano may experience through the seasons. When your piano stays closer
to its correct pitch level of A440 (A-440 cycles per second), your technician does not have to perform a large pitch
raising or lowering procedure prior to fine tuning. Thus, a balance of forces is maintained between the strings and
the frame of the piano, allowing more accurate and stable tunings to be done.

In addition, a stable environment will help to preserve your piano through the years. Wood parts, glue joints, metal
parts and your piano's finish will all last longer if not subjected to excessive humidity swings. Maintaining the correct
environment will preserve your piano investment for a lifetime of enjoyment.

Humidity and the Climate  

Excessive humidity and extreme temperature changes are the enemies of the piano. The piano is basically a
wooden instrument. Too much moisture in the air will cause the keys and action parts to swell, resulting in sticking
and sluggish notes. The felts will, over time, become hard, resulting in a noisy action. The tuning pin block–a
laminated hardwood block into which the tuning pins are driven, will expand around those pins, and then, when the
surrounding are becomes dry and the block loses some of its moisture, will contract, causing the tuning pins to
become loose, resulting in a piano that will not "hold a tune." The steel strings will become rusty and destroy the
tone of the instrument. The other metal parts will, likewise, rust and eventually need to be replaced.

The ideal level of humidity for a piano is around 40 per cent. While it is almost impossible to maintain a particular
level of humidity in a home, certain precautions can be taken. Don’t place the piano near a window or door where it
will be exposed to dramatic changes in outside humidity. Don’t place the piano near an air-conditioning/heating duct.
Don’t place the piano near a fireplace or other source of heat, which will dry out the air.

This brings us to the second "enemy"–extreme temperature change. Many of the things mentioned above relate to
temperature change as well as humidity. While humidity changes will alter the tuning of the piano, temperature
changes will "knock" a piano out of tune even faster. Do not locate a piano where it will be exposed to direct sunlight.
Not only will the sunlight fade the finish, but the piano will go "out of tune" in an incredibly short time. Placing a piano
on an outside wall was, in years past, a "no-no." Insulation techniques and air circulation were poor, and methods of
heating were such that a piano would "sweat" when placed against an outside wall. However, with today’s central air
conditioning, this is not nearly so much a problem.

Protecting Against Humidity  

One excellent way to deal with the humidity problem is to have your technician install a piano de-humidifier. This
device consists of a long aluminum tube containing a heating element which heats to about the temperature of a hot-
water pipe, and a humidistat, which turns the heating element on when the humidity level gets above 40% and off
when the level falls below 40%. The entire unit is installed inside the lower cabinet of a vertical piano, or suspended
directly underneath a grand piano. Power consumption is negligible, and the unit will last for many years. A
humidifier is also available, which plugs into the same humidistat. The humidifier is, in most cases, not really
necessary in the Houston climate.  

Q.  Would New Mexico's climate serve as a good example of an extreme climate that would affect my piano?

A. An excellent example. This climate is a good example that provides wide (often wild) swings in temperature and
humidity.  Pianos like consistent temperature and humidity levels.  What to do?

1) Temperature:

a) Locate your piano against an inside wall.
b) Keep your piano out of direct sunlight.
c) Keep your piano away from drafts, heat sources and air conditioning vents.
d) Keep your piano as far as possible from any fireplace or wood-burning stove.  Fire sucks moisture out of the air-
and your piano-faster than you can say, "My soundboard cracked!"

2) Humidity: (with a little humour added)

a) Keep your piano in a sealed room with a special humidifier that keeps the room humidity at 42% (manufacturers'
recommendation) while making no noise, or . . .
b) install an indoor swimming pool, or . . .
c) install a Piano Lifesaver Climate Control System from DAMPP-CHASER.  I consider these systems so essential to
piano care in New Mexico and similar areas.   Or . . .
d) do nothing-and pray.

To summarize:
Ideally, a piano should be kept in a room with temperature around 70°( ± 5°) and relative humidity around 50%
(±5%). The exact temperature and humidity is not as important as keeping as little fluctuation as possible.  Some
pianos react to conditions differently.  Yamaha and Kawai are known to have moisture proof treated felt parts in an
attempt to avoid some problems with changes due to humidity excursions.  The DAMPP-CHASER Humidistat system
is probably the best general system for establishing consistent humidity levels in extreme environments.  KeyArts /
Japan Pianos U.S.A. furnishes this system for our customers or consult your local piano technician.

Thanks for reading our piano care temp and humidity guide