Humidity & Home
If the outside temperature is 10 degrees the recommended RH of a properly humidified home is 30%. If the temperature is below zero the recommended RH can drop to 15%! Luthiers recommend 45 – 55% RH. The home can be a hostile environment for a guitar; one of the reasons we created the Guitar Humidor™.
The Guitar Maker’s recommendations:
From the Martin Guitar Company site: Your guitar is made of thin wood which is easily affected by temperature and humidity. This combination is the most important single part of your guitar’s surroundings. Martin keeps the factory at a constant 45-55 percent humidity and 72-77 degrees Fahrenheit. If either humidity or temperature get far away from these factory conditions, your guitar is in danger.
Martin also suggests keeping your guitar in the travel case where the small space is more easily humidified.
How Serious is the dehydration to Guitars?
From Larrivee:
Fully 80% of the guitars returned requiring repair have damage which is the result of severe dehydration. Damage due to dehydration is not covered under warranty because it is owner-preventable environmental damage. Many people do not realize how damaging very low humidity can be on a solid wood instrument.
Damage may be permanent and may include neck shrinkage, bridge sinking or lifting, glue joints failing and soundboard cracking.
Properly Humidified Homes are still a hazard to Guitars
The chart below is the chart that comes with an Aprilaire central home humidifier. It is their recommendation for proper humidity levels in a home:
| Outside Temperature (0°F) | Recommended Relative Humidity | ||||
|---|---|---|---|---|---|
| +40 | ° | 45% | |||
| +30 | ° | 40% | |||
| +20 | ° | 35% | |||
| +10 | ° | 30% | |||
| 0 | ° | 25% | |||
| -10 | ° | 20% | |||
| -20 | ° | 15% | |||
If you are interested in reading more there is a very nice publication regarding humidity and home prepared by the Minnesota Blueflame Gas Association corroborates the chart above.
When the temperature outside drops below 40 degrees the relative humidity in a properly humidified home would be well under the recommended RH for your guitar. If the outside temperature is much below 10 degrees Fahrenheit, your home would present an extremely damaging environment for your guitar with a RH of only 15 to 25%.
Non-Humidified environments
It should be pointed out that most homes may not have a central humidifier and would not be considered a properly humidified home. These environments can be many times worse for your instrument. Additionally older homes may have drafts and leaks as well as less insulation and perhaps no moisture barrier, creating a less efficient heating/moisture environment. The more a furnace runs the more moisture it takes from the air and the lower your home’s RH. Therefore older homes are especially prone to be dry. In these cases you might not need very cold outdoor temperatures to have an extremely dry environment. The only way to know for sure is to use a calibrated hygrometer and measure your RH.
Be aware that your humidity will also vary room to room and even by location in a room. Of particular concern would be having an instrument near a hot air vent or outside wall. Air from the furnace is warm and dry and could do damage quite quickly to your instrument. It’s a good idea to always check the RH where your instrument will be.
How long does it take to damage an instrument?
Martin emphasizes that the speed of the change in humidity/temperature is a critical factor. In the winter season humidity in homes can drop very rapidly (overnight) with a cold front. This means that damage can occur quite quickly to an instrument that is not properly protected.
