Dehumidifiers and Humidity Control in Archives and Libraries

Q: What is the best type of humidifier for archive stores?

Typically, archives have very low air change rates, so low-duty systems are usually sufficient. For precise humidity control, a resistive steam humidifier is preferred over an electrode boiler type. This type of humidifier can also be fitted with a room distribution fan if no central ducted air handling system is available.

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Benefits

Proper humidity control in archives, libraries and long-term storage is vital for many reasons.

Preservation of Materials

Keeps paper, books, textiles, and artifacts safe from mold, warping and brittleness.

Prevents Pests and Insects

Deters infestations that could destroy archival materials.

Ensures Long-Term Stability

A consistent environment helps deliver decades and centuries of conservation

Archive & Library Humidity Control

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Dehumidifiers and Humidity Control in Archives and Storage Areas

Preventing excessive humidity protects delicate materials such as paper, textiles, wood, and leather from damage caused by moisture absorption, dimensional changes, and mold growth. Many pests thrive in humid conditions, including booklice, silverfish, and carpet beetles. These pests can damage collections by feeding on archived materials and leaving droppings.

Magnetic and optical media are highly vulnerable to corrosion and data loss in humid conditions. Mold can also pose a health risk to staff and visitors, as well as damage building materials through condensation and corrosion.

Condair dehumidifiers help leading archives worldwide protect collections by controlling humidity and ensuring long-term preservation.

Humidification and Humidifiers for Archives

In cold climates, heated indoor air can have very low humidity, which poses a risk to many natural materials. Paper loses moisture to dry air, shrinks, and becomes brittle. Distortions in leather, parchment, and textiles can cause book bindings to lose their integrity, especially when combined with the drying of adhesives.

As static electricity increases in low humidity conditions, electro-sensitive materials such as film are placed at greater risk.

International standards such as ISO 11799:2015 reinforce the need to control humidity at levels appropriate to the materials in question and the local climate. They also emphasize minimizing fluctuations, as rapid changes in humidity can have the most detrimental impact. Institutions such as the Smithsonian Institution Archives and the National Archives and Records Administration both recommend a minimum humidity of 30% RH, while avoiding fluctuations greater than 5% RH in any 24-hour period.

Energy-Efficient Environmental Control

Heating alone is often mistakenly used to reduce relative humidity but does not lower the absolute moisture in the air, leading to high operating costs. Dehumidification directly removes water vapor from the air, delivering up to 60% energy savings compared to heating-only strategies. This makes long-term preservation both cost-effective and more sustainable.

Use Cases

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Projects and References

National Army Museum, UK

The National Army Museum is the leading authority on the British Army and its impact on society past and present. Condair has supplied and installed three Condair RS resistive steam humidifiers to maintain the humidity around the exhibits and archives.

Rijksmuseum, Netherlands

The Rijksmuseum is one of the world's finest art museums with over 1.5km of galleries and artworks by Rembrandt, Vermeer and Van Gogh. The Condair DL hybrid humidifier is maintaining the ideal humidity for the preservation of paintings such as The Night Watch, The Milkmaid and The Merry Drinker.

ARoS Aarhus Art Museum, Aarhus

Condair DL hybrid humidifiers ensure optimal indoor humidity at The ARoS Aarhus Art Museum, protecting over 1,100 paintings and 400 sculptures.

Precise humidity protects millions of books at Bibliothèque Nationale de France

As one of the most recognisable and symbolically powerful architectural landmarks of contemporary Paris, the Bibliothèque nationale de France (Site François-Mitterrand) sets new standards in cultural design, monumental scale and preservation of knowledge. Condair is proud to contribute to this visionary institution with advanced hybrid humidification solutions that protect priceless collections, ensure visitor comfort and guarantee energy-efficient climate control.
Preserving millions of books, manuscripts, maps and artefacts demands rigorously stable climatic conditions. Optimal relative humidity “crucial for preventing damage to paper, bindings and other organic materials“ is reliably maintained by Condair DL hybrid humidifiers.

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Frequently Asked Questions

What is the best type of humidifier for archive stores?

What is the ideal humidity for an archive?

The ideal humidity depends on two factors: the objects being stored and the temperature stability of the storage area. For organic items such as paper, wood, and textiles, the ideal range is between 35% and 60% RH within a temperature range of 55°F to 68°F (13°C to 20°C). For inorganic items such as metal, a lower humidity range of 11% to 45% RH is typically ideal.

What kind of dehumidifier is best for an archive store?

There are two main types of commercial dehumidifiers: condensing and desiccant.

Condensing dehumidifiers perform well when the store temperature is above 68°F (20°C) and typically below 95°F (35°C). With this technology, humidity levels from above 45% RH up to 95% RH can be achieved. However, reaching low relative humidity levels below 40% RH is more difficult, where desiccant dehumidifiers are required. Condensing systems typically offer control accuracy of around ±10% RH. They also require either a drain connection or regular maintenance to empty condensate tanks.

Desiccant dehumidifiers offer a much wider operating range in terms of temperature, from -22°F to 104°F (-30°C to 40°C), and relative humidity from 0–100%. They can achieve very low humidity levels, even below 10% RH if required, and provide much more stable control, typically ±2% RH or better. They do not require a drain connection but do require a ducted exhaust to vent moist air outside the conditioned space.

Why is it so important to control humidity in an archive?

Items made from organic materials such as paper, wood, and textiles react to changes in humidity and can physically change shape. Repeated fluctuations in relative humidity can cause structural damage over time. In addition, because these materials are organic, there is a higher risk of mold growth at elevated humidity levels.

For inorganic items such as iron or steel, the rate of corrosion (rust formation) is directly proportional to the humidity level. Corrosion can occur up to six times faster at 90% RH compared to conditions below 50% RH.

Will heating alone keep an archive dry?

Heating alone will not keep an archive dry. While it will reduce relative humidity, it does not reduce absolute humidity. Absolute humidity is the mass of water vapor per unit volume of air. Heating also does not change the dew point temperature, which is critical because it is the point at which liquid water can form on object surfaces.

To “dry” an archive, it is necessary to reduce absolute humidity by physically removing moisture from the air. This can only be achieved using a dehumidifier. Heating alone also typically results in higher running costs.

Using a dehumidifier will typically result in up to a 60% reduction in energy consumption compared to direct space heating.