Maintenance: Best Practices

Balance Pins

The following text contains excerpts from the Maintenance chapter of Mario Igrec's book Pianos Inside Out. Some of the cross-references and footnotes were removed.


Controlling the climate is an absolute prerequisite for a piano’s stability and longevity. Humidity and temperature must be kept at acceptable levels and within close tolerances, or the instrument will go out of tune and deteriorate. The first rule is not to place a piano near sources of temperature and humidity changes: poorly insulated outer walls, windows, radiators, directly over or under heating or air-conditioning vents, or in direct sunlight, or a draft. The second rule is to maintain the temperature and humidity at levels as constant as possible. A piano subjected to unstable climate conditions will not hold its tuning, its soundboard will degrade, other wooden parts will crack, the finish will get damaged, and the action will become sluggish or loose.

The effects of climate changes can be reduced to some extent by keeping the lid of a grand piano closed, and the piano draped in a padded cover when not in use. The cover absorbs and releases moisture, evening out changes in humidity, and helps protect the finish.


Humidity affects all materials in a piano. The dimensions of porous materials like wood, leather, and felt change with variations in humidity, while metals oxidize in excessive humidity. Wood swells and shrinks because its hollow cells absorb and release moisture from the air. Because of the composition of the cells, the swelling causes the wood to expand across the grain much more than along it. Consequently, when the grain in a wooden board runs at varying angles, which is almost always the case, the swelling causes warpage. The best way to reduce warpage is to control humidity.

Soundboard and Tuning Stability

As wooden cells in a soundboard swell and shrink due to changes in relative humidity, the board wants to expand or shrink across the grain, but the ribs to which it is attached do not permit that. Since the soundboard is crowned upward to resist the downbearing of strings, its expansion and shrinkage affect the degree of crowning. Expansion increases the crowning, pushes the bridges up, increases their pressure against the strings, and makes the pitch rise. The opposite is true of shrinking—it reduces the degree of crowning and lowers the pitch.

Since the greatest change in crowning occurs in the widest area of the soundboard, the greatest variations in pitch tend to occur in the tenor section. The middle section can be greatly affected as well. For example, a piano in which A4 is tuned to 440 Hz at 50% relative humidity may get above A450 at 90% R.H., while the deep bass and high treble remain close to A440. When the R.H. drops to 10%, the same piano may drop to under A430 in the middle. In some climates, relative humidity in a home without air-conditioning may exceed these extremes.

Measuring Relative Humidity

Relative humidity is measured with a hygrometer. Some home digital weather stations have one or more remote sensors that can be used to measure relative humidity in other rooms or outside. Older spiral-type hygrometers are less accurate than digital units, but even those can vary by 10% or more.

Lowering Humidity

Piano dehumidifiers have come a long way from their beginnings as simple heating rods mounted under a grand soundboard or on the bottom of a vertical piano case. Such dehumidifiers were often installed without humidistats and overdried the piano. Today, heating rods are a part of a complete humidity-control system such as the Piano Life Saver System, by Dampp-Chaser®, which maintains humidity within a narrow, preset range. You can expect a piano dehumidifier to be moderately to very effective for a grand soundboard (more so if a special cover is installed under the piano), not very effective for a grand action, and very effective for both the soundboard and action in verticals. By far the greatest value of a piano dehumidifier is in stabilizing the tuning by maintaining the same moisture content in the soundboard year-round. Tuning pins and strings will not be as well protected in grands. Dehumidifying the air in the room is still the more complete solution, but a piano dehumidifier is quiet, less costly to operate, and more environmentally friendly because it uses a fraction of the energy required by the other solutions.

Moisture-absorbing agents such as silica gel are limited in their ability to remove large amount of moisture, but they do lower humidity and act as a humidity shock absorber. They are not effective in pianos that are kept open or are opened frequently. Music Sorb, by Fuji Silysia Chemical, Ltd., is a synthetic silica gel for pianos and other wooden musical instruments. It absorbs moisture during humid months and releases it back to the air when humidity levels drop. Supplied in attractive moisture-absorber bags, this product can be placed on the grand plate, in the grand action cavity, or on a vertical’s baseboard or key bed. Keep silica products away from children and pets.

Air conditioner: A properly sized modern air conditioner is an efficient dehumidifier in warm climates. Its refrigerant gas is pressurized in a “condenser,” a radiator where the gas is condensed into a liquid. It is depressurized in another radiator, called the evaporator, where the refrigerant turns back into gas. On the pressurized side, the refrigerant is hot; when depressurized, it cools rapidly. Because of the great differential in temperature between the two “sides,” the system removes heat from the room by transferring it to the outside air. The process also removes moisture from the air by condensing it on the cold evaporator coils (whose operating temperature is between 34° and 42°F [1–7°C]). The condensed moisture is drained or evaporated outside. An air conditioner is very efficient as a dehumidifier when outside temperatures reach or exceed 90°F [33°C], even when the R.H. is very high. It is less efficient at lower temperatures or if oversized, because it will then run for shorter periods of time. Some air conditioners have a dehumidification setting, but this is useful only within a relatively narrow temperature range.

Central air-conditioning systems are energy efficient. Select at least a 13 SEER183 unit with an expansion-valve evaporator, and ask your contractor for a system with a built-in dehumidifier.

Air dehumidifier: This relatively inexpensive, selfstanding, portable unit works on the same principle as a refrigerant-based air conditioner, except that both “sides,” cold and hot, are inside the room. The air first passes over the evaporator, where, due to the great cooling effect, the moisture from the air condenses and drips into a removable container. This cool air is then reheated by the condenser coils, now with less humidity. Unfortunately, dehumidifiers heat the air somewhat, and are not practical in warm climates unless air conditioning is also used. These units are equipped with a crude humidistat and will cycle on and off, but don’t expect precision. When the ambient temperature is below ca. 65°F [18°C], the condensed moisture from the air freezes on the evaporator coils and the unit must stop working momentarily to melt the ice. Most units do this automatically by means of a deicing sensor.

Portable room dehumidifiers are noisy, and their water pans must be emptied daily unless you install permanent drainage—through the wall or into a floor drain, for example. The noise and the heat they generate make them impractical to run while you are in the room, and that leads to fluctuations in humidity. However, a dehumidifier helps reduce humidity in the entire piano, and is valuable even when you have a piano humidity-control system.

Central dehumidification: If you have a central air conditioning system, the most effective way to reduce humidity is to retrofit the existing system with a whole-house dehumidifier. Whether or not this expensive solution is justified depends on how effective your air conditioner is as a dehumidifier, and how many months of the year you need additional dehumidification.

So what should you get? Unless you can afford a whole-house dehumidifier, a piano humidity-control system is a safe investment in all but the driest climates, where such systems may not be able to deliver sufficient amounts of additional moisture. In cold, damp climates, a self-standing dehumidifier is a good solution if you don’t use the room a lot. If you keep your house cool, the unit may not be effective, as it will spend a lot of time deicing. In moderately warm climates, an air conditioner should be supplemented with a dehumidifier. In a subtropical or tropical climate, central air conditioning is a must, with additional dehumidification needed during spring and fall.

Increasing Humidity

Relative humidity needs to be increased in dry climates, and when heating is necessary to maintain a comfortable temperature. The easiest way to humidify the air is to let the water evaporate by itself. However, the evaporation at room temperature is slow and would have to occur over impractically wide areas to be of any consequence. Placing a pan or a bucket of water under the piano is totally inadequate.

In buildings with radiator heating, placing pans of water atop radiators will help, but not enough to protect the piano. Well-insulated, radiator-heated houses are fairly easy to humidify, but the piano should be placed away from the radiators. Floor heating can be damaging—turn it off in the area under the piano if you can, and install a piano humidifier. Forced-air heating (hot air delivered through vents) causes a lot of air movement and requires much larger amounts of moisture to be added to the air. Pressurized systems in institutional settings present an even greater challenge because they exchange large amounts of air. If you are considering a piano dehumidifier such as a Dampp-Chaser, you may want to invest in a complete Piano Life Saver System, which includes a piano humidifier. I am less enthusiastic about the humidifier than the dehumidifier in this type of system because it involves more maintenance and its protection is limited to the soundboard in grands (the action and pinblock are mostly unprotected). Still, it is valuable as a way of supplementing other ways of humidifying the air, and will help maintain the tuning year around.

A moisture-absorbing agent such as Music Sorb will moderately increase humidity levels during heating season by releasing the moisture it absorbed in more humid months. It will not be effective if you live in a climate that is dry year-round.

Dusting Between Tuning Pins For moderate humidification, an ultrasonic humidifier may be the best solution. It is virtually noise free because it disperses water into the air via a membrane that vibrates at ultrasonic frequencies. Small ultrasonic humidifiers may not be sufficient for the coldest days, but are inexpensive enough that you can buy several of them. Expect to fill the tank once or twice a day, and to empty and clean the unit weekly.

A small ultrasonic unit may suffice in a mild climate, but if the relative humidity frequently drops below 25%, you should obtain a console or a floor-standing ultrasonic humidifier with more than one tank, or with a water hookup.

In areas with hard water, any ultrasonic humidifier will generate fine white dust, and its membrane may lose its efficiency due to calcification. A water-softening cartridge (make sure cartridges are available for your unit) is an effective way of solving this problem. You may consider installing a water softener or buying a reverse-osmosis filtration system, which removes minerals from the water.

An older type of humidifier has a revolving screen dipped in a pan of water, and a fan that blows air through the screen. Such humidifiers are noisy, bulky, and inefficient. The screen and the pan must be washed often to prevent buildups of dirt, algae, and fungi.

If you already have a central climate-control system that delivers air-conditioned and/or heated air through air vents, consider adding a central humidifier to the system. This may be worth the expense; such humidification prevents health problems, and protects all wood items in the house with less maintenance.


Sudden fluctuations in temperature, for example when stage lights are turned on or sun hits the piano, have an immediate effect on pitch. The effects of temperature and humidity are complementary—while heat stretches strings and lowers their tension, it also lowers relative humidity. This decreases downbearing force and further reduces string tension.

Allowing the room’s temperature to fluctuate seasonally—higher in the summer and lower in the winter—helps moderate fluctuations in relative humidity, and is also a good idea from the standpoint of energy conservation.

Preventing Damage by Insects and Rodents

Pianos have a lot of felts and cloths, which attract clothes moths. The best prevention may be to avoid high humidity and to periodically vacuum the interior of the piano, including all accessible felts and leathers. Promptly dispose of the bag contents, which may contain eggs, larvae, or even adult moths. Some piano owners report good results from placing a small bag of dried lavender or cedar balls in the action cavity. (Make sure the bag won’t interfere with the keys or the action.) A concentrated lavender oil or gel may be another beneficial repellent, but keep in mind that both lavender and cedar lose their effectiveness as their aromatic oils dissipate—replenish them frequently.

Moth balls and crystals can be effective in an air-tight environment, but it is not clear how long the piano would need to be sealed, and they may damage plastic parts in the action. Keep in mind that most vertical pianos have openings in the back, and that their front panels are not air-tight. You may want to place moth traps inside the piano. If you are not sure whether you have an active infestation, that will prove or disprove it.

Whatever repellent you use, air the piano from time to time to avoid the product’s possible corrosive effects, and to expose the larvae to light. The brighter the light, the more disruptive it is to moth larvae. For more information, read “Clothes Moths: Integrated Pest Management in the Home,” available at

Wood-boring insects are a problem particularly in warm and wet climates. The most common are woodworms, which sound like crickets as they eat their way through wood. They create small exit holes, under which you may find a small amount of wood dust. Woodworms progress slowly, but can create a lot of damage if left untreated for a long time.

Termites are as much a threat to pianos as to any wooden structure. Severe infestations can leave whole parts of the piano, such as legs or parts of the case, hollow, just waiting to collapse.

Mice and rats are known to nest in pianos left untouched for a long time. They will damage wood and felt, and will bunch fibrous material as bedding for their offspring. The best way to protect against them is to keep the house rodent-free.

Infestations should be treated promptly by professionals. Don't try to clean an infestation yourself to avoid exposure to diseases that are spread by rodents.

Preventing Corrosion

Humidity is not the only factor that promotes corrosion of metal parts. Woods, glues, and finishing materials in pianos release acidic gases that attack all metal parts, from strings to tuning pins, springs, action center pins, key pins, even key leads. Corroded leads can expand so much that they split the keys and block the entire keyboard. Trying to depress the keys of such a keyboard results in further damage.

The best way to avoid corrosion is to periodically air the piano. Keep the fallboard open at all times, or at least during the day. Whenever playing a grand, open its front lid; in a vertical, open the top lid from time to time.

Periodic Maintenance


Pianos should be tuned at least once a year or more often, depending on the amount of use and seasonal changes in climate. Aside from the obvious benefits, tuning a piano regularly promotes pitch stability, allows servicing the piano humidifier/dehumidifier, and provides an opportunity to address any other problems. Learn more about our tuning services.


Like any fine mechanism, the piano action, keyboard, dampers, and pedals need to be regulated periodically. Learn more about our action, keyboard, and damper regulation services.

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