Humidity Question - How does temperature affect proper RH for Guitars?

[rpg51]

This is an issue I have been meaning to ask about for some time. 

Assume for the purpose of discussion that the ideal condition for my guitar is 70 degrees and 45% Relative Humidity.  If my guitar is unfortunately kept in a room where the temperature is 90 degrees, not 70 degrees, what RH level is best - higher than 45% RH, lower than 45% RH, or exactly 45% RH?  If the RH should be different that 45% how can I calculate or estimate the proper RH. 

Now, same question but the temperature is 55 degrees ....

[johbren]

I wish I could answer that. I too get confused I went out and bought a planet waves hygrometer right now it says 51%at 69 degrees F that is a good range ive had it up to 70% at 80 degrees a few days ago and as low as 36% at 68 degrees this past winter when the humidifier wasnt putting out cause the filter was clogged and you know what my Larry never complaind a bit.

[Calvin]

The way I understand it, you just set the RH.  Because the guitar is in equilibrium with air in terms of water content (i.e. there is no tendency for water to go either the guitar's or the air's way).  While it's true that hot air at same RH has more moisture, it can also hold more moisture (so eventhough there is more water in the air, they dont mind staying there because they can).

I have one guitar that's actually too wet because I had a case humidifier lol (it's fine now, poor baby :GRN>).

[Steve]

If the amount of water vapor is held constant, then if you;

--reduce the temperature, the relative humidity goes up

--increase the temperature, the relative humidity goes down.

If you add more moisture to the air then RH will change also.  Here is a link that helps you to understand RH.

Humidity and Temperature

I have one guitar that's actually too wet because I had a case humidifier lol

I once purchased a used OM-21 from a guy.  He said that the sound just didn't do it for him.  When I got it I could smell mildew in the sound hole and it sounded like it was full of socks.  After I got it dried out in a week or so out of the case, it sounded like a bell, just beautiful!  It was just to wet from a sound hole humidifier!  I still have it and it has a wonderful tone, I can't part with it even though it's a Martin. :GRN>

[Ratishna]

Hard and fast criteria don't really exist.  You don't want it too hot and damp or too cold and dry.  But the sweet spot in the middle is a lot bigger than you might think.

E. Shoaf

[rpg51]

The way I understand it, you just set the RH.  Because the guitar is in equilibrium with air in terms of water content (i.e. there is no tendency for water to go either the guitar's or the air's way).  While it's true that hot air at same RH has more moisture, it can also hold more moisture (so eventhough there is more water in the air, they dont mind staying there because they can).

I have one guitar that's actually too wet because I had a case humidifier lol (it's fine now, poor baby :GRN>).

So the idea is that if the guitar is at 90 degrees it can hold more water than it can at 70 degrees without distorting?  And that is what happens if you keep the RH the same at both tems, correct?   The wood fibers actually will have more water in them at higher temperatures.  And it works the other way too - lower temperature, same RH, means less water in the wood fibres?  Right?  But like the air the guitar can hold more water at higher temps without showing any signs of swelling????  I've got to say this is a little hard for me to grapple with.  Doesn't make much sense to me.  I would have thought that you would want to lower the RH at higher temperatures so that the guitar has the same amount of water in the wood fibers as it does at lower temperatures???

I know this is probably not all that important but for some reason I find it interesting. 

[Calvin]

RH is how much water air can hold, has nothing to do with your guitar.

Guitar just has x amount of water it needs.  So lets say it's hot out, the air is holding alot of moisture (say RH is 50%), but that doesn't mean it's going to go inside your guitar if your guitar's moisture content (not relative) is the same as the air.  There is no pressure for the water to move eitherway.

Yes.  Hotter air has more moister per same RH value.  But then since it has no problem of holding it in the air, the water will not go into your guitar unless your guitar is significantly more dry.


...or so I understand. :GRN>