Keeping your guitar at a comfortable temperature is critical for its longevity. Avoid exposing your guitar to hot, dry air during the winter months. In this climate, relative humidity can drop to as low as 25 percent, which can cause issues linked to extreme cold and hot weather. The ideal humidity level for guitars is between forty and fifty percent, although this may vary depending on where you live. It's also important to consider the relative humidity of the environment in which your guitar is stored. Using a digital hygrometer will help you determine what level is best.
If you're storing your instrument in a basement, consider using a dehumidifier to maintain a consistent 45%-55% humidity level. A guitar with high humidity can be prone to string rust, which can indicate a serious moisture problem. Another option for storage is an attic, which has a tendency to be warmer during the day. In such a case, you should keep the guitar away from air ducts and heating systems.
Although temperature alone is not as damaging to your guitar as humidity, extreme humidity conditions can cause significant damage to your guitar. Humidity affects how much moisture is in the air. Although most wood is tolerant to changes in temperature, extreme changes can cause serious damage. Heat weakens glue and weakens lacquer, while cold chills wood and causes "crazing" (a network of fine cracks).