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I live in the Midwest USA, so that means that it is about 0 degrees Fahrenheit this time of year, or lower. This means that my home's heater is put to work in the winter months.

I purchased a humidity monitor which tells me that recently the humidity has been as low as 20% in my room with the temperature at 72 degrees Fahrenheit. Is it bad to store instruments such as violins, acoustic guitars, and electric guitars in this room? How so?

The instruments are never stored in their case; they sit on a rack in the open air.

This question, What is the proper humidity range for an acoustic guitar?, reveals that

A wooden instrument is ideally kept at about 40-60% humidity

But what will happen to a wooden instrument that is stored in a room with 20% humidity for long periods of time?

If low humidity is to be avoided at all costs, is the only solution to purchase a humidifer unit (to increase the humidity of the room and counteract the effects of a heater)? Of course, one resolution is to shut off the heater, but my comfort supersedes my instruments' comfort, naturally.

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When storing guitars and other instruments made of wood, one of the most important consideration is the environmental conditions that the guitar will be subject to during storage. This would include extremes of temperature and most importantly, relative humidity.

Wood is very susceptible to relative humidity levels (basically the amount of moisture in the air). Too little humidity and the wood drys out and your guitar can develop any number of problems. Conversely, if your guitar is exposed to conditions where there is too much moisture in the air, the wood can swell and cause different problems. Here is a link Humidity and Guitars that tells you more about how humidity can affect an acoustic guitar and the optimal humidity range.

Many people choose to store their guitars and other wood instruments in a hard-shell case with either a sound hole or an inside the case humidity control system.

There are several sound hole humidifiers that work great for acoustic guitars stored in their case. Here are some of the popular varieties.

Planet Waves Soundhole sponge humidifier This gadget drops in the sound hole and is suspended by the strings. You wet the small sponge inside whenever it dries out.

enter image description here This is a Dampit Soundhole instrument humidifier. It can be used in instruments with F holes as well as larger soundholes so it will work with violas or cellos for example. Again it uses a sponge to hold moisture.

enter image description here This is another Planet Waves Product called Humidipack and is a two way humidifier. According to the description on
Planet Waves dot com this is a

maintenance free, two-way humidity control system for guitar. It automatically maintains the optimal 45-50% relative humidity level within your instrument case, eliminating the guesswork and potential mess related to refilling a humidifier. Unlike refillable humidifiers, this system provides true “two-way” purified humidity control by adding and removing moisture on demand.

There are also many YouTube videos describing how to make a simple homemade humidifier using a sponge and something like a plastic sandwich bag with small holes punched in it. By making your own, you can size it to conform to any instrument or to whatever air space (however tight) might exist in your instrument's case. I have found that denser sponges tend to hold moister longer than the cheaper light weight ones. You can cut any sponge to fit the size you need.

If not all of your wood instruments are stored in a hard shell case or if you want to leave one on display or handy so you can play it daily without removing it from the case - you might consider a room humidifier to maintain the optimal humidity level in the room where your instruments will reside. Many models of humidifiers will automatically maintain a pre-set humidity level. You set the level and then leave it on. When the humidity drops below the pre-set level, it will automatically come on and run until the desired humidity level is restored.

A room humidifier will not work well in a wide open space. Ideally it should be used in a room with a door that can be kept closed during the dry heating season. You might also add some foam weather stripping to seal any gap below the door to make it even more efficient.

Regardless of which method you choose, it is important to maintain an adequate humidity level for the health of your instruments. With 20% or below, I am afraid your instruments may be susceptible to deleterious effects of drying.

Good luck.

  • What's interesting is that I have stored my wooden instruments on a rack in this very low humidity environment for several winter seasons now and I haven't noticed any issues. (I did not buy a humidity monitor until recently, and thus was wholly unaware of just how low the indoor relative humidity level sank during the winter.) Do you think that I just got lucky? – Bolt Dec 15 '16 at 20:41
  • Not all guitars are as susceptible as some. The most intolerant are acoustic guitars with solid wood tops backs and sides made from less dense woods such as spruce and cedar. Mahogany and maple can tolerate lower humidity due to the density of the wood. – Rockin Cowboy Dec 17 '16 at 0:37
  • You focused on the acoustic guitar in your answer, as did the website you linked to explaining the effects of low humidity on a guitar. Are solid-body electric guitars/basses as vulnerable under low relative humidity levels? All of the instrument humidifiers that I've ever seen are designed to be inserted into an instrument's sound hole (which a solid-body obviously lacks, perhaps implying that humidifiers are not obligatory for a solid-body instrument). But, then again, solid-body electric guitars are still made of wood...so I don't see how they would be any different. – Bolt Dec 17 '16 at 2:27
  • @Bolt Solid Body Electric Guitars tend to be less susceptible to humidity levels than acoustics. The wood in solid body electric guitars is typically well sealed with a finish topped by varnish or lacquer that seals the wood and inhibits the loss or absorption of moisture. Acoustic guitars on the other hand have raw exposed wood in the inside of the body and often have a lighter finish on the outside of the body to facilitate more responsiveness since the vibrations in the body are what produces the sound. Too much lacquer on an acoustic may dampen the sound. Not so on electric. – Rockin Cowboy Dec 18 '16 at 20:13
  • Ah, that makes sense. I only have two acoustic instruments, but I am going to take your advice and get my humidity level under control, because I'd hate to see any damage to my instruments. After all, the electric guitars still have wooden fingerboards, and I'd imagine that fingerboards are not as well-sealed as the bodies. Just look at the havoc that dry air did to the sealed exterior of this upright piano - yikes! – Bolt Dec 18 '16 at 22:33
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At low humidity the wood will dry out and contract (shrink). This will put stress on instrument and can cause parts of it to crack or for (glued) wood joints to come apart.

Other than room-wide humidification, the most common approach is to use miniature humidifiers that go into the instrument case with the instrument. A search on "instrument humidifier" should point you in the right direction. Basically you end up using the instrument cases as tiny humidity controlled rooms.

Exposing instruments to somewhat low humidity for a few hours a day while you use them should not adversely affect them.

  • Good tip about the instrument humidifier, but I have 7 instruments and some of the instrument cases (e.g., for an electric guitar) are too snug to squeeze a humidifier in there. So, it seems like buying a room humidifier probably makes more sense (both in terms of price and convenience) than buying 7 humidifiers and a couple new, larger cases. – Bolt Dec 15 '16 at 18:31
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Solid wood instruments like mid to high end acoustic guitars are actually quite sensitive to humidity. It probably depends a bit on what wood(s) an instrument is made of and how the wood is seasoned.

When the ambient relative humidity is low, water will evaporate out of tone woods. When it is high, tone woods will absorb water from the atmosphere. The wetter wood is, the more dense it is and the more it swells to a larger size, and vice-versa for dryer wood.

The density of a masterial greatly affects its sonic properties, so we would want the correct moisture content in our instruments to get the best sound. What's more critical is the swelling and shrinking of tone woods as their humidity changes. This can cause quite serious permanent damage to an instrument. Even short of damage, the sizes of the different materials do not all change in the same proportion, so the instrument geometry can be thrown off leading to all kinds of problems with tuning and playability.

Most instrument manufacturers recommend keeping instruments in their cases for protection. This also helps with temperature and humidity changes, and you can merely humidify your cases instead of an entire room. If you don't want to keep instruments in their cases, then a humidifier and possibly dehumidifier is necessary to preserve them properly.

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I have found that what hurts instruments the most is sudden and violent changes in temperature or humidity. If you can keep the humidity and temperature relatively constant trough the year, you should be OK.

It is things like an extended car ride in the boot of your car that has it in it to kill your instrument. I can direct you to a famous guitar dealer who I recently saw a video discussing this topic.

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    Agreed that extreme changes can do more harm that gradual - however constant low humidity is never good for wood which will dry and crack and shrink in the absence of enough humidity. – Rockin Cowboy Dec 15 '16 at 18:39

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