I am often bewildered at some of the comments I hear with regard to humidifying a guitar. Most music stores will try and sell humidifiers that fit in the guitar sound hole as the preferred method for humidifying your guitar and although these products vary in their effectiveness, they may not be the best source for a well balanced moisture content. I will explain this later in this post but first it is important to understand simply how relative humidity works.
Understanding Relative Humidity and Temperature
Relative Humidity (or RH) is a measurement in percentages of the how much moisture that air is holding relative to the air temperature and the dew point (dew point equals 100% Relative Humidity or RH). When the temperature drops by one degree, the relative humidity will actually increase by 2.2%. This is why we often see dew outside in the morning time during certain times of the year. Since the objective is to keep a balanced RH around your guitar, it is safe to say that keeping a guitar (especially acoustic guitars) in an environment that has major swings in humidity and temperature will destroy the instrument. First, you want to make certain that the room that you keep your guitar or guitars in maintains a fairly stable 72 degrees and that the guitar is placed away from windows, exterior doors and sunlight. Secondly you want to spend a few bucks on a descent hygrometer so that you can monitor the relative humidity in that room.
The RH of the room that you keep your guitars in should maintain a reading of 40 to 55 percent. Too many days consistently below 40% RH and you will begin to notice that the finish has a corduroy look to it, the action has changed and even cracks occur in the top, back or sided of the guitar, just to name a few of the problems that can occur as a result of a low relative humidity. Too much humidity can cause a bloated effect and since mold and fungus typically require 55% RH (or higher) in order to become active or "alive" or non-dormant, the guitar can actually develop patches of mold and fungus.
In The Case or Out?
I am often asked "should I keep my guitar in the case or out?" and my answer is.......maybe. I'll explain; If you have a room that you can maintain the RH between 40% to 55% during most months of the year then by all means keep the guitar on a guitar stand and leave it out of the case as the guitar wood will maintain a more balanced moisture content. If you do not have a suitable room for this, then your next option should be to keep it in your guitar case with a sound hole type of humidifier. I suggest this as a second option because there is no real control of the humidity inside the case, and guitar cases are usually lined with products that absorb moisture. While the inside of the guitar box can get so much moisture that fungus grows other parts may just get enough or too little. Worse yet, guitar players using these type of humidifiers often forget to systematically "wet" the humidifier causing it to have a reverse effect as it dries out and then tries to absorb the moisture from the air inside the case.
How do I do it?
I am in a climate where only few months out of the year are not humid enough and so for me I keep my completed guitars in a climate controlled room. Because wood is like a sponge it will hold the moisture for a little while and so I will run a humidifier in the room once per day unless we are having a cold spell. What works for me here at Hawkins Guitar in Virginia Beach Virginia may not work where you are but if you understand how relative humidity works it should help you set up an environment that is good for your health and your guitars health.