A piano consists of about 10.000 parts. Most of them are made of wood.
Since wood is an organic materia, it is easy to understand that a climate with small changes in temperature and humidity is by far best for your piano.
In Scandinavia we have dry, cold winters and humid, warm summers. The extreme seasons affect the moisture content in our instruments. Tuning stability and a reliable function of the action are affected solely by the change of this moisture content.If you just have bought an expensive instrument it would be a good idea to consider a device for climate control. My advice to you is:
Piano Life Saver System.
It creates a micro-climate around your instrument and near the soundboard that will keep the humidity around 42% at evert time of the year!
I happen to be a certified field installer of this system. (See below)