Symptoms of a Dry Guitar
If your guitar displays any of these symptoms, it is most likely in need of humidification.
• Sharp fret ends
• 14th fret hump’
• String fret buzzing (low action)
• Sunken top
• Flat back (no arch)
• Loose bracing
• Cracks or seam separations
• Lacquer checking (small cracks in a nitrocellulose finish)

Proper Care of Acoustic Instruments
Acoustic instruments are built in environments where air is kept
between 18 and 24 degrees Celsius and 45-55% relative humidity (RH).
To avoid damage, you should keep your guitar within these ranges.
Keeping your acoustic guitar in a hard shell case during periods of low relative humidity is the single most effective way to protect your instrument from damage. The humidity inside your home in the middle of the winter in Canada can dip as low as 10% RHl
Humans are affected by low RH as well. Do you get dry skin or itchy eyes, or experience static shocks walking across your carpet? If you have these symptoms, then your acoustic sitting out on its stand in this kind of environment is suffering too
Using a sound hole humidifier and placing the guitar in the case, away from heat vents, will protect your instrument when it is not in use. During very cold weather, check your sound hole humidifier a few times a week. Sponge-type humidiers must not be allowed to stay in the instrument when they have dried out. The sponge will re-absorb moisture back from the guitar! Keeping a digital hygrometer inside your case will tell you instantly the RH of the environment around your guitar.

Instead of humidifying the guitar in the case, you can keep your guitar out but humidity the room with a cool or warm mist room humidifier. This only works if you can keep the room between 45-55% RH. If the room has windows or weak insulation, humidity in these ranges in interior heated rooms can cause condensation around colds spots, possibly resulting in the development of mold. Using a case is a much simpler solution.
Don’t forget about your guitar’s fretboard. Most acoustic guitars have either rosewood or ebony fretboards. These pieces of solid hardwoods can lose humidity just like the thin pieces of the solid wood body. As the fretboard loses moisture, it will shrink. The frets, being metal, will not – and therefore will protrude from the edges of the neck

Periodically, run your hand up and down the edges of your fretboard and feel for any protruding ends. You can place a case humidifier in the neck area of your case to introduce the moisture back into the fretboard. When performing a string change. take the opportunity of having the strings off the neck to clean and condition the fretboard. Get rid of fingerboard gunk and polish the frets at the same time by rubbing 0000 steel wool the length of the board. After wiping it down, apply some fretboard conditioner to the board and rub it with your fingers. Let it sit for a few moments and then wipe off the excess.

Do: Keep your guitar in its case when not in use.
Do: Use a sound hole humidifier and check it regularly.
Do: Leave your guitar in the case when bringing it in from the cold until it has come up to room temperature. Taking a cold instrument out of the case into a warm room will cause rapid movement of the wood, leading to crazing, checking and possibly cracks in the wood.
Do: Keep the case closed while you are playing your guitar so as not to lose the stored up humidity.
Do: Use distilled water in humidifiers to increase their longevity. Do: Condition your fretboard periodically to keep it from drying out
Don’t: Leave your instrument out on a stand near heat vents.
Don’t: Keep papers, sheet music, cardboard or other paper products in the case with the humidified guitar. They will absorb some if not all of the humidity from the guitar.
Don’t: Allow a sponge type humidifier to get dry inside the guitar. It will start to pull humidity FROM your guitar, becoming a dehumidifier.
Don’t: Get too close to the fireplace during your winter sing-a-longs!
Don’t: Allow any water on the surface or inside the guitar. Guitars need moisture VAPOUR, not water. Water will damage the guitar.

The important thing to remember is to use common sense. If the environment is making YOU uncomfortable, then your guitar is uncomfortable. Your-skin doesn’t react well to dry conditions. You don’t like huge changes from hot to cold or cold to hot and your guitar doesn’t either. You wouldn’t put your pet in the trunk of your car in the winter would you? Treat your guitar like your cherished pet. It won’t lick your face but you’ll get years of enjoyment from it nonetheless