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More about the indoor climate in historic churches

Historic churches are of great cultural and historical value and play a valuable role in society. The building often offers a wealth of information about the history and development of a specific region, but also offers information about structural and architectural abilities of yesteryear. Therefore its preservation is essential!


Finishing and decoration of the historic interior is generally done with valuable but climate-sensitive materials such as carved wood and frescoes. Heart of the interior is often the historic church organ. Depending on the age of the church this organ is already in use for centuries. From practice is known that in recent decades historic church organs frequently are affected by a change in indoor climate. Formerly, when the church was unheated or only locally heated with for example foot stoves, the climate inside the church was very stable all year round. Especially after the introduction of warm air heating the church climate got out of balance. With warm air heating the church is being violently heated before a service with inlet air temperatures up to 100°C.

  Fluctuation in the indoor climate cause by heating

This heating strategy in the church causes large fluctuations in temperature, but more importantly significant fluctuations in relative humidity (RH). In particular this surge in RH is the culprit behind many damage processes to historic organ and interior. What happens exactly during the heating of a church with an air heating system? The chart shown at the right side displays the measured temperature and RH in a historic church organ during a typical Sunday service. In the early morning the heating system is switched on manually, so the temperature in the higher placed organ rises from 12 to about 25°C within a few hours. RH in the organ falls considerably within this short time frame, due to the physical relationship between temperature and relative humidity. In this example, RH drops from 50% to 25% in only a few hours.


As warm air rises, the higher parts of the church volume -often containing the organ- are much warmer and drier than air in and around the pews. As a result of this decrease in RH hygroscopic materials like wood start desorbing moisture. These objects can get deformed and even permanently damaged by cracking or delamination. In historic church organs wooden pipes and wooden wind drawers often suffer the most, detuning the organ or even making it unplayable. An extensive organ restoration is inevitable. Depending on the size of the organ the cost of such a restoration can rise up to hundreds of thousands of Euros. When restoring an organ, a thorough evaluation or renovation of the heating system therefore is essential, to prolong the restoration interval substantially.

 Fungal growth on a wooden organ pipe

Current insights show us that the climate in a historic church is essential for the preservation of building, interior and organ. The building can suffer greatly because of an incorrect climate. During services often a lot of moisture is released in the church, caused by individuals and an improper heating strategy. This excess in moisture can condensate on cold surfaces of the structure and may cause mold growth or damage to valuable stained glass windows.


The church heating system plays an essential role in the preservation of building, interior and organ. Modern church heating systems therefore are not only designed for thermal comfort for occupants, but also for optimizing the indoor climate for conservation of the historic building, interior and organ. These systems are designed for high energy efficiency, for example using low temperatures or using local heating.


Please contact us in case of any questions, or browse through our reference projects for an impression of our method.



Last Updated on Friday, 13 November 2015 16:02