Temperature controlling the collections

May 12, 2025 | Treasure tales and archive snippets | 3 minute read

At Holkham Hall, we have rooms full of treasures that have been collected over hundreds of years. From Old Masters paintings to ancient marbles to tapestries, there are many different materials to care for in our collection.

Anthony van Dyck’s portrait of the Duke of Arenburg in the centre of the room. Mr and Mrs D Carver

One of the mains ways in which we can ensure that these items are staying in the best condition they can be is through environmental monitoring and control. The main environmental factors that we are looking at when carrying out monitoring are Temperature and Relative Humidity (RH), as well as light levels.

At Holkham we use two environmental monitoring systems, one called Eltek and one called TinyTag. The Eltek system is typically used for areas where we need to monitor the conditions across a whole room, for example in the State Rooms or Libraries. This monitors temperature, humidity and light levels. TinyTag is used where we need to look at the conditions in a specific area, such as in display cases or on bookshelves.

The Eltek monitors send data directly to our Collection Teams computers so they can track what is happening throughout the day. Wherever we can, we aim to keep our temperatures between 18°C and 20°C, and the RH between 40-60%. If we keep our conditions within these parameters, this keeps things comfortable for both our collection and our visitors. Data from the monitors is downloaded every three months and is analysed by our Collections Coordinator, who can then compare to previous years and decide if any additional measures need to be put in place.

When conditions fall outside these parameters it can cause problems and damage for the collection. Having temperature or RH that is too low can cause materials to become brittle, whereas if they are too high this can lead to problems with damp, warping and mould. Keeping the conditions just right helps the collection to stay in good condition and reduce the need for remedial conservation treatments in the future.

Using heating is the best way to control the RH, as an increase in temperature will bring the humidity down. Over the years, there have been various heating systems installed through the Hall. The first central heating system was installed in 1843 for the newly married 2nd Earl and Countess, in time for their first winter at Holkham. This was based on the original hot air system, of which air vents can still be seen around the Hall today. Today, the heating in the Hall operates on a hot-water system which is powered by biomass boilers using wood from the Estate.

If you visit the Hall, you may see equipment around such as heaters, dehumidifiers and fans. These may look slightly out of place in our wonderful historic Hall, but they are working hard to keep those conditions stable and protect our interiors and collections.