Recommended Dehumidifiers for Archival Storage of Documents and Electronics

Archival storage rooms require much more than a dry environment. Documents, books, photographs, magnetic media, computers, circuit boards, and other electronic equipment can deteriorate when temperature and relative humidity (RH) fluctuate excessively. For this reason, choosing the right dehumidifier for archival storage is an important part of long-term preservation.

The Library of Congress recommends relatively dry, stable conditions for many paper collections, while the National Archives emphasizes continuous monitoring and control of temperature and RH.

What Humidity Is Best for Archival Storage?

There is no single RH target that is ideal for every archival material. However, 30–50% RH is a practical range for many document and mixed-media storage environments.

For example, the Library of Congress recommends approximately 30–55% RH for most books, while its guidance for paper materials often recommends around 35% RH.

For mixed collections containing documents and electronics, a good starting target is generally 40–50% RH, provided the collection does not contain materials requiring specialized conditions.

The key is stability. RH above 60–65% increases the risk of mold and material deterioration, while excessively low RH can make paper brittle and may create problems for some materials.

Why Use a Dehumidifier in an Archive?

High humidity can cause several problems:

Mold and mildew growth

Paper deformation and deterioration

Corrosion of metal components

Oxidation of electronic contacts

Condensation on cold surfaces

Damage to packaging and storage boxes

Musty odors

Increased insect activity

For electronics, humidity control is particularly important because moisture can contribute to corrosion and electrical reliability problems. Archival facilities therefore need to control not only the average RH but also rapid changes in environmental conditions.

A dehumidifier should work together with the building's HVAC system rather than being considered a replacement for complete environmental control.

Recommended Types of Dehumidifiers

1. Commercial Refrigerant Dehumidifier — Best for Most Archive Rooms

For a typical document archive, records room, library storage area, or electronics warehouse, a commercial refrigerant dehumidifier is often the most practical choice.

These systems cool air below its dew point, condense moisture on an evaporator coil, and then return drier air to the storage room.

Advantages

High moisture-removal capacity

Relatively energy efficient in moderate temperatures

Suitable for continuous operation

Automatic RH control

Available in portable, wall-mounted, and ducted configurations

Suitable for medium and large archival rooms

A commercial dehumidifier with built in humidistat can maintain a predetermined RH set point instead of simply running continuously.

Recommended application:
Document archives, libraries, records centers, museums, office archives, and general electronics storage.

2. Low-Grain Refrigerant Dehumidifier — Best for Moisture Emergencies

An LGR dehumidifier is more appropriate when an archive experiences flooding, roof leaks, pipe failures, or other water-damage events.

LGR technology can achieve lower dew points than conventional refrigerant dehumidifiers, allowing it to extract moisture from relatively dry air more aggressively.

However, an LGR unit is usually not the first choice for everyday archival climate control. It is better viewed as restoration equipment for rapidly reducing moisture after an incident.

For example, after a water leak, an LGR dehumidifier can be combined with air movers to accelerate drying and reduce the duration of elevated humidity.

3. Desiccant Dehumidifier — Best for Low-Humidity Requirements

A desiccant dehumidifier removes moisture by passing air through a moisture-adsorbing material rather than relying primarily on condensation.

This makes desiccant technology useful when an archive requires:

Very low RH

Precise humidity control

Low-temperature operation

Stable conditions in specialized storage

Moisture control for sensitive electronic components

Some archival materials require conditions significantly below normal room RH. For example, certain photographic and film materials may require specialized low-temperature and low-humidity storage.

For these applications, a desiccant system may be preferable to a conventional refrigerant dehumidifier.

Dehumidifier Comparison for Archival Storage

Dehumidifier Type	Best Application	RH Control	Low-Temperature Performance	Typical Role
Commercial Refrigerant	Documents, books, general electronics	Excellent	Good	Primary humidity control
LGR	Floods, leaks, restoration	Excellent	Good	Emergency drying
Desiccant	Specialized archives, sensitive electronics	Excellent	Excellent	Low-RH applications
Portable Residential	Small, non-critical storage	Moderate	Limited	Small archives only

For most document and electronics archival storage rooms, a commercial refrigerant dehumidifier is the best balance between capacity, energy consumption, reliability, and cost.

What Features Should an Archival Dehumidifier Have?

Choosing the technology is only the first step. A good archival dehumidification system should provide precise and stable environmental control.

1. Accurate Humidity Sensor

Choose a unit with a reliable RH sensor and adjustable humidity set point. A system that can maintain approximately 40–50% RH is suitable for many general-purpose archival environments.

2. Continuous Drainage

Archives may require 24/7 humidity control. A continuous drain connection eliminates the need to empty a water tank and reduces operational interruptions.

3. Automatic Restart

Automatic restart is valuable after a power outage. The dehumidifier should return to its previous operating mode without requiring staff to restart it manually.

4. Low-Temperature Operation

Storage rooms can operate at relatively low temperatures. A dehumidifier designed for low-temperature operation can continue controlling moisture without excessive frost-related interruptions.

5. Ducted Installation

For larger archives, a ducted commercial dehumidifier can provide more uniform air distribution than a portable unit.

Ducting also allows the equipment to be installed outside the collection room, which can reduce noise and simplify maintenance.

6. Remote Monitoring

Wi-Fi, alarms, Modbus, or other building-management interfaces can help facility managers monitor RH continuously.

This is especially valuable for valuable collections because an unnoticed humidity excursion can cause significant damage over time.

Recommended RH Settings for Documents and Electronics

A practical starting point is:

Documents and books: approximately 30–55% RH
Mixed archival storage: approximately 40–50% RH
General electronics storage: approximately 40–50% RH

Sensitive photographic/film collections: specialized conditions may be required

These should not be treated as universal specifications. Different materials have different preservation requirements.

The National Archives, for example, specifies RH set points between 35% and 50% ±5% for certain archival environments and emphasizes limiting daily fluctuations.

Therefore, stable humidity is often more important than simply choosing the lowest possible RH.

How to Choose the Right Dehumidifier Size

Dehumidifier capacity should be calculated based on more than floor area.

Consider:

Room volume

Outdoor air infiltration

Number of door openings

Building envelope

Local climate

HVAC operation

Number of people entering the room

Moisture generated by adjacent spaces

Desired RH set point

Required recovery speed after humidity excursions

For a well-sealed archive with stable HVAC conditions, the continuous moisture load may be relatively low. Conversely, an older records warehouse with frequent door openings may require substantially more capacity.

For large archives, it is generally better to perform a moisture-load calculation rather than selecting a dehumidifier based solely on square footage.

Dehumidification Is Only One Part of Archival Preservation

A dehumidifier cannot compensate for poor storage conditions.

The Library of Congress recommends keeping collections in clean, climate-controlled environments and avoiding attics, basements, and garages because of temperature, humidity, and water-damage risks.

An effective archival storage strategy should combine:

Stable temperature

Stable RH

Proper ventilation and air circulation

Air filtration

Leak prevention

Appropriate storage boxes and enclosures

Protection from sunlight and UV

Regular environmental monitoring

Pest management

Adequate drainage and emergency response

For valuable collections, environmental sensors should continuously record temperature and RH so that staff can identify trends before they become preservation problems.

Final Recommendation

For most archival storage of documents and general electronics, a commercial refrigerant dehumidifier with precise RH control, continuous drainage, low-temperature operation, automatic restart, and remote monitoring is the best overall solution.

For flood or water-damage emergencies, choose an LGR dehumidifier for rapid drying. For archives requiring very low RH or specialized low-temperature humidity control, a desiccant dehumidifier may be more appropriate.

The most important principle is not simply "keep the archive dry." It is to maintain a stable, controlled environment appropriate for the specific materials being preserved. This reduces mold risk, limits moisture-related deterioration, and helps extend the useful life of both paper records and electronic equipment.