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Pianos & Humidity Control

The second most important thing you can do for your piano after tuning, is to control the humidity in the environment that the piano is being kept in.

There isnít a piano made that will stay in tune if it is exposed to dramatic swings in humidity. The parts of a piano are made of metal, felt and wood. The cast iron plate and steel strings are not greatly affected by high humidity or extreme dryness. But the felt and wood components will swell with rising humidity or shrink when the air dries out.

When the wooden bridges, soundboard and back posts of a piano swell with the summer humidity, the pitch of the strings will rise. Unfortunately, because the strings are all different lengths, the pitch does not rise evenly. The reverse happens when the heat comes on in the fall and the inside air starts to dry out. The shrinking wood will allow the tension to come off the strings and the pitch drops accordingly.

Piano technicians know from experience, that pianos in concert halls, which are tuned throughout the year will always follow a predictable pattern. When the season starts in the early fall, the piano will be slightly above pitch from the summer humidity. Throughout the fall the pitch of the piano will have dropped a little each time they come back to tune. This goes on until the spring when the humidity starts to rise. From that point on, each time they return they will find the piano has crept up in pitch and has to be brought back down to concert pitch. This continues until the fall and then the whole cycle starts over again.

Uncontrolled humidity swings can do more harm to a piano than just affecting the tuning. High summer humidity and extreme winter dryness can cause cracks in the soundboard and bridges. The cracks will appear in the winter when the wood shrinks but the high summer humidity may have been the cause, as the wood crushed together when it expanded only to separate when it dried out. Extremes in humidity can also lead to sluggish or sticking action components. I always get the most calls to fix sticking keys in the dead of winter and during a summer heat wave.

What does this mean for your piano?

You can prevent damage from humidity swings by
  1. never placing a piano on top of a heating vent.
  2. If you have a grand piano close to a forced air vent, place a baffle on it to direct the flow away from it. This will protect it from having the heat collect under the soundboard.
  3. Donít place your piano in a south facing picture window. The sun is lower in the sky during the winter and it will bake the piano every afternoon in what is already the driest time of the year.
  4. Have a good humidifier installed on your furnace.
  5. Use your air conditioner throughout the summer. It will draw a huge amount of moisture out of the air and it will prevent the piano from absorbing it.
  6. Have a humidity control system installed in your piano. I used to just install the Dampp-Chaser® System in pianos that were in problem locations where the lack of humidity control was causing major problems. But after years of seeing how well they work to stabilize pianos, I would recommend them to anyone that has an expensive instrument that they want to preserve.

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