Pianos and humidity

From time to time I get jobs that involve fixing loose tuning pins on pianos. The pins (which maintain and control tension on the strings) are generally between 50 and 65mm long and are driven into a thick piece of wood called the wrest plank.

The reason I mention this is to raise the topic of how humidity can affect your piano. Although temperature changes can make a difference, a piano is likely to be fairly happy as long as the variation isn't too extreme. More problematic are changes in humidity - specifically relative humidity (the amount of water vapour in the air as a proportion of the saturation point at any temperature). Relative humidity can easily be measured using a hygrometer - these can be purchased very inexpensively from shops or on the internet (left-hand picture shows an analogue type, the right-hand one a digital; these are both combined thermometer/ hygrometers). Hygrometers generally need to "settle" in a room for a certain length of time before giving a true reading.

Generally speaking, pianos are happy with relative humidity in the central range (40 to 60%); allowing humidity to get lower or higher than this for long periods may cause problems. In practice, high humidity conditions can occur when pianos are stored in locations such as unheated outbuildings or the piano is in a damp or cold place (possibly close to a poorly-insulated outside wall). Low humidity however is a more common problem in modern centrally-heated houses because during the winter cold air from outside is heated without adding any moisture, so the relative humidity drops very rapidly (warm air can hold much more water vapour than cold air). For example, if air at 4ºC is taken in from outside at 80% relative humidity and heated to 22ºC inside the house, the humidity level drops to just 25%.

Common symptoms of low humidity conditions (35% relative humidity or less) are:

• Loose tuning pins due to drying out of the wood in the wrest plank. These can sometimes be fixed, but tuners will charge for doing this and in some cases may have to install a new string since the pin may need to be removed to fix the problem
• Soundboard (and sometimes other wooden parts) may start to crack or split

An important point to note is that older pianos (because of the materials used) are generally much less tolerant of very dry conditions that newer ones. If you can't keep your piano in a cooler place and a fairly long way from radiators during the winter, then consider getting a more modern instrument.

Problems that may be associated with damp (over 65% relative humidity) conditions are:

• Film of rust may appear on steel strings and tuning pins, and verdigris on copper
• Mildew on wooden parts
• Veneer peeling on case
• Keys and action parts sticking or sluggish
• Problems can result when the piano dries out (e.g. things coming unglued).

Alleviating the problem of very low humidity

• If a hygrometer shows there is a problem, consider putting the piano into a room other than the main living room (dining rooms are a popular choice) where the heating can be kept on a slightly lower setting during the winter
• Otherwise see if you can turn the heating down a little generally
• Keep the piano some distance away from any radiators or other direct heat sources
• Keep it out of direct sunlight if possible
• It is possible to purchase humidity control systems, though these are only likely to be a sensible investment for more expensive pianos.

Leaving a jar of water laying around in the room will not be enough to make any significant difference to the humidity, though putting it inside the base of an upright with the top closed might just be enough to help a little - however if you do, remember that it's there when you move the piano and don't spill it or it could cause damage.

Oddly enough, allowing the temperature to fluctuate a little more in the room (cooler in winter and warmer in summer) may help to moderate the humidity variations that are so bad for your piano.