Climate Control 

Climate control is important because inappropriate temperature and relative humidity (RH) can severely limit the lifespan of paper collections. High temperature increases the speed of the chemical reactions that cause deterioration.  High relative humidity provides moisture to fuel these reactions—the higher the humidity, the more quickly deterioration proceeds. Relative humidity that is too low can cause documents to dry out and become brittle. 

Temperature and RH are interrelated—a change in one will bring about a change in the other. Managing temperature and relatively humidity levels is referred to as climate control. 

As a first step towards limiting deterioration by good climate control, an institution should aim at maintaining stable conditions year round, no higher than 70°F and between 30% and 50% RH. If possible, a lower temperature is better for your collections; however, RH should not be allowed to get too low or damage from drying out can result. Generally, you should try to keep RH no lower than 30%. 

Keep It Steady

The more fluctuations there are in temperature and relative humidity, the more deteriorating effects there are on your collections. And, to take this a step further, the more rapid the fluctuations occur, the worse it is for your collections. So maintain the most stable climate possible over time. 

If you had a choice of two storage climates for your records, which one would you choose? 

Environment 1
This storage area is located near an office work area with heating and cooling systems. Although the temperature and relative humidity aren’t monitored, the climate is generally people friendly – with temperature between 65 and 70 degrees and a stable humidity level. 

Environment 2
This storage area is one of those rooms that is “hot in the summer” and “cold in the winter.” During the cooler months of the year, the temperature stays between 50 and 60 degrees Fahrenheit and RH is generally around 60%. During the warmer months, the temperature stays between 70 and 80 degrees and RH is generally about 40%. 

Click here to view the answer.

When the temperature is lowered, the RH will rise--and when it reaches 100% the air will become saturated and moisture will condense out. (This is called the dewpoint.)

Keep it steady!

How Can You Tell If the Climate is Okay? 

There are many monitoring devices that help you monitor your climate. The key to monitoring your climate is to record the measurements systematically. Once you have recorded measurements over a period of time--several weeks at a minimum, you can evaluate your climate and determine whether or not you need to take action. 

What Do You Need To Monitor the Climate? 

At a minimum you need reliable thermometers and humidity monitors in all your storage areas. These don’t have to be expensive, but they do have to be reliable!   

Humidity can be measured using Humidity Indicator Cards, available from many archival suppliers. These cards usually cost less then $10 for a package of five cards.   

Or for about $70, you can purchase a hygrometer. 

For about $100 you can purchase a simple thermohygrometer (also called a hygrothermometer) that measures both temperature and RH.   

You can also purchase digital versions of hygrometers and thermohygrometers – although they are most expensive. And if you want to monitor continuously, you can purchase a hygrothermograph.   

Your equipment doesn’t have to be complex and digital. You can monitor climate using a reliable thermometer and hygrometer for about $100. If you combine this relatively inexpensive equipment with a chart where you write down the temperature and humidity readings every day for several weeks,  you have a sound climate control system. Remember to monitor climate in all your storage areas! 

You can purchase climate monitoring equipment from a variety of vendors, including traditional archival supply companies and scientific instrument companies.

What If the Climate Isn’t Okay?

If your climate is less than perfect, you should consider taking some actions to improve the situation. Remedies could include:

Installation of central environmental controls Use of portable air conditioners, humidifiers, and/or dehumidifiers Removal of collections from attics, which tend to be hot, or basements, which can be damp Improvements in insulation and building seals

Be sure to continue to monitor the conditions once you've made changes so you can make any additional necessary adjustments.

A hygrothermometer is a device that gives readings of temperature and relative humidity.

A hygrothermograph is a monitoring device that is placed in a storage room to monitor and automatically record temperature and humidity at certain intervals.  It records the measurements on a scaled paper chart.

Want to learn about some other climate monitoring devices? Click here to read a technical leaflet from the Northeast Document Conservation Center.