Humidity Control

Humidity Control

Humidity is a big killer of pianos! if regulation or tuning stability is a problem (or there are old glue joints in the piano) we insist that a humidity control system be fitted.

We supply and install systems designed for pianos, keeping the relative humidity at ~42%.

Read all this section – it is important for you to understand the consequence of climate on your piano.
All Wood Shrinks and Swells with Humidity Changes – even your Piano!

Sticking Drawers – When humidity levels in the air are higher, you may notice that some of your cupboard drawers stick. This is because the wood absorbs moisture from the air and swells.

Sticking Doors – You may have a door that works perfectly in dry seasons, but sticks when the humidity goes up.

Loose Furniture Joints – Glued wooden joints become loose and wobbly when the air in your home becomes dryer from winter heating or from a change to dry weather.


Sticking Keys – Just as doors and drawers become tight with high humidity and loose in dry air, the keys of your piano may stick down when struck in times of high humidity. When the environment surrounding your piano is dry the keys may seem to rattle when played.

Sluggish Action – As you play your piano, you will notice how responsive the keys are to your touch. The way the keys cause the wood (felt covered) hammers to strike the strings is part of thousands of interconnected wooden parts called the piano action. With high moisture levels in the piano action, the action is sluggish, and the keys seem non-responsive to your touch.


Bridge and Soundboard Damage – The Soundboard is the largest piece of wood in your piano. It actually vibrates to amplify the sound produced by the strings. The bridges of your piano are joined to the soundboard and support the strings.

MOIST CONDITIONS – As the soundboard absorbs moisture from the air surrounding the piano, it swells, producing an upward bulge. Through the bridge, this put additional tension on the strings. Now the pitch is too high in the lower mid range and extreme treble string.

DRY CONDITIONS – When the soundboard shrinks and flattens, the tension of the strings over the bridge becomes inadequate. The pitch of the mid-range and treble strings is now flat.

CRACKED SOUNDBOARD – Over time, constant changes in humidity levels, with the corresponding shrinking and swelling of the soundboard, will damage the integrity of the soundboard. You will often see crack in the soundboard due to humidity damage.

Pin Block Plank Damage

MOIST CONDITION – The strings of your piano are held tight by the pins in the pin block plank. As the plank absorbs moisture in periods of high humidity, it swells, crushing the wood fibers against the pin.

DRY CONDITIONS – In dry periods, the wood shrinks away from the pin, loosening it and causing the string to sag. When this cycle is repeated time after time, the wood fibers surrounding the pin are destroyed and lose their resilience.

DAMAGED PIN BLOCK – With continuous swelling and shrinking, the wood in the plank is often no longer able to provide a snug fit required to hold the pins in place.

String damage

RUSTED STRINGS – The strings of your piano are responsible for producing the musical sound. With exposure to high humidity levels over long periods, strings become rusted and corroded.

RUSTED TUNING PINS – At the junction where rusted strings wrap around rusted pins, rust corrosion forms a hardened bond between the two. Then, during a tuning, when your piano technician turns the pin to stretch the string, the inflexible rusted string snaps at this point.


A Climate control system fitted in your piano maintains your piano at an average 42% relative humidity as recommended by major piano manufactures. When your piano soundboard is kept at a constant moisture level, shrinking and swelling are minimized.

Your piano goes out of tune when the humidity in the environment surrounding the piano changes. The humidity levels in your home environment are controlled to some extent by the temperature. Generally, an air conditioner will remove some humidity, but when there is a drop in humidity when dryness set in, presents a significant moisture change which will put the piano out of tune. When your piano is maintained at 42% relative humidity, it will stay in tune longer and better.


The Climate Control System is made up of three basic components which work together to control the humidity levels within your piano, maintaining the recommended average 42% relative humidity, no matter what the external conditions are.

HUMIDISTAT – this is the brain of the system, which senses whether the wooden parts of the piano are too moist or too dry.

DEHUMIDIFIER – carries moisture away from your piano using air currents when humidity levels rise.

HUMIDIFIER – moisturises the dry wood of you piano when the humidity drops below 42% RH.

These components cycle together to maintain the wood of your piano at 42% RH. When the humidistat, located less the 25 mm from the soundboard, senses that the wood is dry, it turns the power on the humidifier. Then, when the humidifier has provided enough moisture to the soundboard, the humidistat turns off the humidifier and turns the power on to the Dehumidifier. The Dehumidifier carries away moisture from the soundboard on air currents until the humidistat again senses that the soundboard is dry. The system again switches to the humidifying function. The cycle continues day after day, year after year, protecting your piano from external conditions.

The control system comes with a watering system to allow you to keep the humidifier supplied with about 4 lts of water.

The system is installed out-of-sight in your piano


The early 20th century saw peak production of pianos as economic prosperity permitted many families to own a piano. Thousands of those vintage pianos survived the years and are now being restored to their original condition. Today, leading piano re manufacturers strongly recommend the installation of a climate control system to prevent continued wood cell deterioration and metal erosion in the older piano.


A piano is best placed on an inside wall away from direct sunlight, heat and air flows. Reading the above you should understand the effects of climate on the piano. Sometimes a piano can be placed on an external wall if the wall is insulated.

Often you hear people say a piano shouldn’t be place on an outside wall, this came about in the days when homes where weather board and had scrim walls and no insulation. However if you are concerned about the placement of you piano then you are best to ask when we come and tune it for you.