Relative Humidity Overview

What is Relative Humidity (RH)?

RH is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. RH depends on temperature and the pressure of the system of interest. It requires less water vapor to attain high relative humidity at low temperatures; more water vapor is required to attain high relative humidity in warm or hot air.

RH is normally expressed as a percentage; a higher percentage means that the air–water mixture is more humid.  

In cold climates, the outdoor temperature causes lower capacity for water vapor to flow about.  Therefore although it may be snowing and at high humidity relative to its temperature outdoors, once that air comes into a building and heats up its new RH is very low.  This results in very dry air, which is a hostile environment for a guitar and the primary reason we created the patented ClimaStand.

RH and Your Guitars

The recommended RH for guitars is 45 – 55%; however, 40-60% is generally considered acceptable.  This is not a subjective range of one luthier, but rather a consensus across the board from every luthier on the planet.  

From Taylor guitars website:

"Proper hydration is vital to the performance of wood products like guitars, whose stored moisture can be robbed by dry, thirsty air. In fact, extended exposure to dry conditions poses one of the biggest threats to a guitar’s health. As a guitar loses moisture, the wood shrinks, which not only compromises the playability and sound of the instrument, but can also lead to cracking and other damage. If you notice your guitar’s action getting low and buzzy, or feel your frets protruding as you move up and down the neck, it’s likely a symptom of a dry guitar. Even if you don’t currently see or feel these symptoms, your guitar could still be dry. Maintaining proper guitar humidity levels will help you keep your guitar in top playing condition."

There is also some really good information from our friends at Santa Cruz Guitar Company.  Make sure to click the header for Temperature and Humidity.

RH and Your Home

Additional issues occur within the home which can make RH control difficult to manage for both human comfort and the health of your guitars.  For example, unless you live in an arid climate, periods of high humidity create a myriad of problems for structures and people. Symptoms of high humidity would include:

These conditions will also hold true in climates that go through seasonal temperature swings, which is really a majority of North America.  When the temperature drops, we turn on the furnace and simultaneously the humidity levels inside the house drop.  The following chart shows just how low the RH can get inside a house at typical winter temperatures.

Indoor vs. Outdoor Humidity Comparison Tables

Outside Temperature Outside Relative Humidity Indoor Humidity with Indoor Temp @ 72 degrees F
-10 degrees F 40% 1%
60% 2%
80% 2%
0 degrees F 40% 2%
60% 2%
80% 5%
10 degrees F 40% 4%
60% 5%
80% 7%
20 degrees F 40% 6%
60% 8%
80% 11%
30 degrees F 40% 8%
60% 13%
80% 17%

 

We’ve all felt the depleting effects of dry conditions on our bodies. Think of a long flight spent in an airplane cabin, where the humidity can drop below 15 percent. Or the parched interior of a home being heated during cold winter months, where the humidity can sink into the single digits. Our eyes and skin get dry, we get thirsty, and in extreme cases we might even get a headache or a nosebleed. Therefore, it's no surprise that most people attempt to humidify their homes to make it more comfortable to live in.  When we start to introduce humidity to combat the dry air, we wind up with the same undesirable high humidity issues listed above.

What About a Single Room Humidifier?

A common used technique is to humidify a room where guitars are stored using a single room humidifiers.  Keeping the air in the 45-55% range over the course of a winter is more than most homes can handle. Water or ice will appear on windows and it can migrate into walls and attic cavities. After a few winter seasons, homes may begin to experience molding, rotting, and deterioration. Eventually homeowners will have to pay for repairs and replacements, but it can also result in poor health.

Another important topic to consider is that most people like to vacation from the colder climates during the winter.  During these times, you cannot simply just run your room humidifier dry and hope for the best.  

What Is the Best Method to Keep Guitars Safe?

So we as guitar owners hit a fork in the road - how do we tackle the issue that guitars want to be at 45-55% RH and the limitations and ramifications of humidifying our homes to that level?

There are several options for guitar owners with varying levels of effectiveness and work involved to achieve proper levels.  Sponges are an option that has been available for quite a while.  A very popular model is the Oasis OH-1.  Although effective, they still require regular monitoring and maintenance to ensure the sponge doesn't dry out.  A more reliable method is to utilize our method by employing the D'Addario 2-Way Humidification packets.  Click here to learn more about the Acoustic Remedy Humidification System, which includes not only the packets but also a sealed interior environment.