Relative Humidity
Organs are composed primarily of wood and soft metals. As with anything made of wood, the organ goes through immense changes throughout the seasons. Violinists and other string players are acutely aware of relative humidity as lack of moisture in the air can damage their instruments.
Wood acts much like a sponge. As the moisture level in the air increases, wood expands, primarily across the grain. Likewise, when the humidity level drops, wood shrinks. While this change is not easily perceptible to the eye, it can amount to as much as a 2% change in the width of a board throughout the course of a year. In a large panel this might be 1/4" or more.
Wide humidity swings do great damage to organs and everything else made of wood. Consider the following example: The temperature outside is 35° and the relative humidity outside is 40%. If we heat this air to 70° without adding additional humidity, the relative humidity has dropped to under 12%. By means of comparison, the average relative humidity in the Sahara Desert is 25%. During the summer, it is not uncommon for the relative humidity inside a non-airconditioned room to reach 70% or higher. The result: a 60% swing.
Obviously, the best choice is to manage the relative humidity throughout the year, adding humidiy in the winter and removing it in the summer. Most churches, however, either do not or cannot increase the humidity to acceptable levels in the winter. The best alternative is to do minimal heating during the winter, i.e. heat only for times when the building is in use, and maintain a minimum temperature of 50–55° the rest of the time.
To calculate the relative humidy indoors, enter the outdoor temperature and relative humidity, and the indoor temperature into the calculator at the left. Press the "Calculate" button and you can see the indoor relative humidity.
