Relative Humidity

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Relative Humidity

Postby Jason Johnson » Wed Nov 07, 2012 2:34 pm

Hello all....Sorry if this is not the proper place for these questions. This is the only place I can think of to find expertise.

I've been playing for about 30 years, but I have only used one nice electric Gibson Les Paul (91) for the longest time. Now, after acquiring many different ethnic acoustic instruments from all over the world, and I find myself being worried about relative humidity.

I keep my instruments in a dry basement, and I am worried that the humidity is creeping down to 40% since I have been monitoring it. I hear that 45-55% is necessary to make sure it doesn't dry out. After looking at some consumer reports, I decided on getting a Crane elephant humidifier since the room is quite small (150 or so square feet). The issue is that on full blast, it only seems to get it to 43%.

My questions are:

1. How concerned should I be about this storage environment at 43%?
2. If so, what's the best way to increase the humidity even more? Whole-house humidifier might work? Something else?
3. How concerned should I be about my 5 year old insruments that have not had any increase in humidity? (I am sure I will ask the lutheir the next time I have them setup/corrected).

Thanks for your time...

Regards,

Jason
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Re: Relative Humidity

Postby Bob Gramann » Wed Nov 07, 2012 2:50 pm

I like to keep my house above 40% to protect my instruments. (I build in the 40 to 45% range). Before you do anymore, find a way to calibrate your hygrometer. Most affordable hygrometers aren't very accurate--you can spend a long time chasing a non-problem. Calibrating it near the value that you want (and at a temperature very near the temperature of your basement) is most useful. If you are near where the humidity for your area is measured by the weather folks, you can take it out in the middle of the day and compare to the public reading at that time. I use a psychrometer (you can Google that) to calibrate mine. You can make a psychometer with two identical thermometers and a small piece of cotton cloth.

Not everyone agrees with me, but I am very wary of whole house humidifiers that attach to the furnace. When they work, they're great, but they have the potential to leak and damage the furnace. I had a neighbor whose home caught fire when corrosion caused by the humidifier allowed the gas to escape. I humidify my whole house in the winter with two large tabletop units. I like the Hunter units with the permanent wicks. I don't like the noise they make.

If your instruments haven't cracked yet, or even if they have, your goal is to keep them properly humidified in the future to protect them.
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Re: Relative Humidity

Postby Jason Johnson » Wed Nov 07, 2012 3:00 pm

Bob Gramann wrote:I like to keep my house above 40% to protect my instruments. (I build in the 40 to 45% range). Before you do anymore, find a way to calibrate your hygrometer. Most affordable hygrometers aren't very accurate--you can spend a long time chasing a non-problem. Calibrating it near the value that you want (and at a temperature very near the temperature of your basement) is most useful. If you are near where the humidity for your area is measured by the weather folks, you can take it out in the middle of the day and compare to the public reading at that time. I use a psychrometer (you can Google that) to calibrate mine. You can make a psychometer with two identical thermometers and a small piece of cotton cloth.

Not everyone agrees with me, but I am very wary of whole house humidifiers that attach to the furnace. When they work, they're great, but they have the potential to leak and damage the furnace. I had a neighbor whose home caught fire when corrosion caused by the humidifier allowed the gas to escape. I humidify my whole house in the winter with two large tabletop units. I like the Hunter units with the permanent wicks. I don't like the noise they make.

If your instruments haven't cracked yet, or even if they have, your goal is to keep them properly humidified in the future to protect them.



Gotcha - thanks. I do not see any damage so far, but I will take them in locally to make sure.

I have used three different monitors, this one "seems" to be accurate, but if it stays above 40, I won't be too alarmed. Thanks for the info on the whole-home versions. If it starts to seep into the below 40% range at all, I guess I will just try a beefier tabletop unit. Thankfully, they don't seem too expensive. I will take a look at the Hunter.
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Re: Relative Humidity

Postby Bob Gramann » Wed Nov 07, 2012 3:30 pm

"Seems" accurate may not be close enough. I have several of digital hygrometers. The best is within 2 points of actual, the worst is sometimes 20 points off depending on the temperature--that one was advertised as "accurate" by StewMac. The others are usually off around 10 points on the face reading. Until you check yours, you don't know. The one I depend on is a $150 Abbeon unit which was advertised as "certified." I still had to calibrate it when I got it. Once calibrated, it has held. I check it at least once a year.
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Re: Relative Humidity

Postby Randy Roberts » Wed Nov 07, 2012 10:38 pm

Jason,
I, and the vast majority of builders here, agree with Bob with exclaimation points.
I have 8 digital hygrometers (OK, there was a sale <g>), and 4 home made hygrometers, that I spent a day calibrating with my psychrometer. Of the digitals, one was right on (until a week later, when it was off by 14%), 3 were within 6% plus or minus, and 4 were 10-15% off. They were a mix of models of 3 different brands. I stuck a piece of tape on each with how much it was off, but don't trust any of them.

The homemade ones have been remarkedly accurate, and are easy to make. They have also been quicker to reflect change in the humidity than the digitals. Just sanded a piece of baltic birch plywood down to two plies and glued it to a staff with a scale on the bottom. It does take running through several days of varying humidity to mark the scale on them.

The point is that you have to be able to calibrate to the truth, and the truth is only found in a wet bulb/dry bulb thermometer (psychrometer).
Without that you really don't have a clue. The microenvironment the instruments are in may vary wildly from where the reading the newscast gives is based on .

You are best off at whatever humidity the guitar was built at in the first place, which you probably won't be able to know, but most hand builders try to build around 40%. If your ethnic instruments were built in the tropics during monsoon season, then 40% might be a problem, but otherwise you should be fine there.
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