Frank French 

Tuning, Repair, Restoration 

Humidity Control 

The Climate of Western Colorado is hard on pianos, most especially older pianos that have made their way to this desert ciimate sometime during their lifespan from a place with higher humidity.  If  the relative humidity in your home is 30%  or less there is a good chance the piano has dried out and gone flat over time.  During the summer months when many homes here are running  swam coolers there will be an increase in relative humidity in your home .  It is the ongoing fluctuation between dryness and higher humidity that has the strongest effect on de-tuning pianos and sometimes affecting moving parts in the piano’s action and pedals causing Irritating noises, sticking notes and a generally sluggish feeling in playing. 





Fluctuation in humidity is the main contributor to the piano going out of tune over time  with the usually going flat as it goes out of tune over time.   Nearly every piano that has not been serviced within one year will go  noticeably flat from its correct pitch . Extra effort is required to bring the piano to its proper pitch in a  procedure known as pitch correction before the piano can be finely tuned.  Very often two or more visits will be required to stabilize the piano at the right pitch.  Over the course of time there will be other adverse effects through neglect of proper and timely maintenance.  Costly repairs usually are the long term result .


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.  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.   For a general idea of expense please see the Climate Control Page


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. 

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How will humidity control benefit my piano?

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. 

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. 

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. 

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. 

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. 

For a copy of this or other PTG Bulletins and Pamphlets, or a list of PTG members in your area, vist the PTG web site or contact Piano Technicians Guild, Inc., 4444 Forest Ave, Kansas City, KS, 66106. Ph: (913) 432-9975 Fax: (913) 432-9986 E-mail ptg@ptg.org

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The preceding article is a reprint of Technical Bulletin #1 published by the Piano Technicians Guild, Inc. It is provided on the Internet as a service to piano owners. 

Piano Technicians Guild is an international organization of piano technicians. Registered Piano Technicians (RPTs) are those members of PTG who have passed a series of examinations on the maintenance, repair, and tuning of pianos. 

© 2009 Frank French

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