The temperature of a pipe organ’s various components and the stability of these temperatures are, over time, the biggest determining factors in whether a pipe organ sounds in tune or not. A pipe organ will sound its best whenever it is at the same temperature as when it was last tuned. We usually request that this temperature be set to 70 degrees Fahrenheit or 21 degrees Celsius for several hours before any tuning begins. (The organ can also be tuned to a different baseline temperature within one or two degrees if desired.) Any temperature changes must be done gradually at no more than two degrees Fahrenheit per hour and a pipe organ will lag behind the room temperature-wise by several hours. In short, the room in which the organ resides must be returned to this baseline temperature several hours before the organ will be heard.
For a performance or tuning on a Friday for example, this may mean that any heating or cooling of the space may need to begin the day prior so as to obtain the desired gradual temperature change and a period of stability following. To the extent that such things can be controlled, room temperatures should never fall below 60 degrees F (15.5 degrees Celsius) or climb over 80 degrees F (26.5 degrees Celsius). This is not to say that the room must be kept at the same temperature all the time for the pipe organ; the climate control can be relaxed during the evening or other times when the sanctuary will be vacant to save expense.
The organ can also withstand a range of humidity between 35% and 75% RH, with occasional drops or spikes beyond these points. For greater tuning stability, an even tighter range in the 45% to 55% range is ideal. Again, it is important that any changes to the level of humidity not be hasty but are carried out gradually to give the organ’s many wooden components time to adjust to the lack of or increase of moisture in the air. This is a concern for any wooden furnishings including pianos – not just the organ!
When planning changes to or replacing an existing HVAC system, an organ’s pipes should never be exposed to conditioned (heated or cooled) air coming from a climate control system. Blowing hot or cold air directly on organ pipes will significantly affect their tuning and will cause them to badly sound out of tune with the balance of the instrument. Any air conditioning or heating outlets should be placed well away from the organ and should never direct forced air towards the organ. Rather, it is recommended that any ducting and grilles for HVAC purposes in the organ area should be used for air returns to promote air circulation.