Piano Dehumidifier

Like all important questions the answer to the question "do I need a piano dehumidifier?" is not a simple yes or no. A better question might be "Do I need to control the humidity around and inside my piano?".

It is reasonable to assume that this is an important question for you if you have invested a substantial sum of money in a high quality piano and either you, or a family member, play the instrument. If so the answer is a resounding yes!

While it is certain that many of you know the answer to this question a word of explanation is called for to explain briefly the reasons for those of you who may not.

In the case of a piano this can result in problems. The wooden soundboard of the piano is not flat, it has an arch, known as a "crown". The crown gets a little larger or smaller with changes in its moisture content and, because this changes the tension on the strings the piano goes out of tune. The more extreme the fluctuations and the more occasions on which they occur the more likely it is that the soundboard will need to be re-built or the entire instrument replaced.

Excessive changes in humidity can affect other wooden parts of your instrument too but there is no need to dwell on them. All piano experts agree that excessive changes in humidity are harmful to your piano and that, therefore, humidity needs to be controlled.

The simplest way to understand this is to imagine two bottles, a one pint bottle and a two pint bottle. If the one pint bottle contains half a pint of water and the two pint bottle contains one pint, each bottle is half full. Each bottle has a "relative fullness" of 50%. That is to say each bottle contains 50% of the water it could contain relative to its total capacity, despite the fact that one holds twice the amount of water as the other.

Cold air, the one pint bottle, can "hold" less water than warm air, the two pint bottle. At 10C degrees, air with a relative humidity of 50% will be "holding" around 5 grams of water per kilogram of air. At 25C degrees air, at the same relative humidity, 50%, will hold 10grams of water per kilogram of air, twice as much.

The relative humidity is what is important, not the amount of water in the air. By keeping the relative humidity within a narrow enough range we minimise the transfer of water from wood to air, or air to wood.

The ideal relative humidity for a piano is 42% and most piano manufacturers recommend maintaining a range of 40% to 50% relative humidity. That range may not be achievable in some circumstances but most informed commentators agree that it is more important to limit the range in which humidity changes than it is to stay within the recommended upper and lower limits. In other words if you can keep humidity within a range of, say 50-60%, that is better than 40-55%.

This is why the question at the top of this page was rephrased. This is not just a question of using a piano dehumidifier, we also need a piano humidifier. Too low a level of relative humidity is just as harmful as one that is too high.

There are two aspects to this problem.

The terms piano dehumidifier and piano humidifier only apply in this context because they are being bought specifically to control humidity around the piano. They are straightforward domestic devices.

The piano dehumidifier and/or humidifier you purchase must have the capacity to sense the relative humidity in the room and to switch on or off when the threshold is achieved. The device that performs this function is called a humidistat. Since you need a piano dehumidifier and humidifier you can rely on, it is advisable to purchase from a reputable manufacturer and not simply buy the cheapest; but neither do you need the most expensive, with all the bells and whistles.

Apart from the humidistat there are three important things to consider:

1. Capacity - the piano dehumidifier or humidifier should be able to cope comfortably with the size of room in which you wish to use it. If your room is a little close in floor area to the maximum the manufacturer claims it is good for, buy "one size bigger". We always give this advice because data presented in manufacturers' specifications is collected under ideal onditions and your conditions are likely to be less than ideal.
2. Automatic restart - if there should be a power outage you will want the machine to restart automatically when the power is restored.
3. Quietness - less important for some but essential for most musicians. Look for a machine that is reported by users to be quiet.

There is on the market a system which fits, out of sight, in the piano itself. It is a combination of piano dehumidifier and piano humidifier, controlled by a humidistat, which maintains the interior of the piano at the optimum level of relative humidity. You can see the components of this sytem in the image below.

It is called the "Piano Life Saver" and is manufactured by Dampp-Chaser (yes, two "p"s is correct).

Its advantages are its precision and unobtrusiveness. Its principal disadvantage is cost. It can only be supplied by a licensed installer and costs several hundred dollars in the US or pounds in the UK.

It is not an alternative to the domestic devices, rather it is an enhancement, a second line of defence. If your budget will not run to both we recommend that you control humidity in the room first and only add the "second line" if and when resources allow.

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