Climate Control Systems
Humidity Control for Pianos
Because pianos are mostly made of woods, there is one optimum humidity that can be said to be beneficial to pianos, which is between 40-50%.
It's important that the wood and glue joints not get too dry: for them a good humidity is desirable. On the other hand, for the metal parts, more than 50% humidity is not needed, otherwise they will tend to oxidize or rust, and action parts will often stick when the moisture in the air rises above a certain level. But the worst thing for wood or wire is to have sudden or severe humidity changes, which can cause soundboards to crack or split, or condensation to form inside the piano, usually on the strings. Humidity changes are often responsible for a host of other undesirables: White spots on piano finishes; the need for more frequent tunings, as strings go out of tune in response to the soundboard swelling and contracting; glue joints cracking and opening up, and cracks or splits in the finish, in the soundboard, pin block, lids, legs and/or other structural members.
Outdoor vs. Indoor climate
Most people worry about moving their piano to a different climate, but it's important to remember there are actually two types: outdoor and indoor. The place where people seem to run into the most problems with any kind of piano (whether targeted for a so-called U.S. climate or not), is when they fail to have any concept of extreme, or rapidly changing, humidity conditions inside their home. By this I mean that there are homes where the humidity was so high you could feel it: it felt damp and muggy, and the piano owner wondered why keys and action parts on the piano were sticking, and why the strings were covered with rust. On the other hand, if you run your furnace in the winter to the point where the humidity in your home drops to 10 or 20 %, be aware that it can cause damages to the soundboard, and/or pin block. No piano will survive conditions like these for long. Depending on how well your home is insulated, the indoor climate may be quite different from that outside. Try not to park your piano close to sources of direct sunlight, radiators, aquariums, bathtubs or showers, heating registers, etc.
How to keep an eye on the piano
It is recommended to keep an hygrometer, which measures the humidity level in the room. This meter can be purchased from your local hardware store.