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Shop humidity: Am I nuts to focus on dew point instead of relative humidity?
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Shop humidity: Am I nuts to focus on dew point instead of relative humidity?
Not sure if this is the best place for this, but whatever. I need somebody to check my logic here–I could be completely wrong in my thinking.
I’m about to start up my new shop in Ireland, and the humidity/temperature situation is VERY different than the Greater Washington DC region. I will also be unlikely to have as complete control over temperature and humidity as I did in our extremely tight, air-conditioned house in the US. I also know my customers won’t either, by and large.
For example, where I am today it’s 5 degrees celcius (40F) and 93% relative humidity, which is standard for this time of year, and easily twice the humidity often seen at that temperature in the DC area. Compared to the guideline of 74F and 45% RH for guitar storage (and generally shop conditions), that’s way too cold AND too wet. I know though, that cold air holds less water than hot, which is why 30% humidity in Arizona is super sweaty, but feels bone dry in Ireland.
That made me question what was the constant that the recommended temperature and humidity represented. I think that constant is Dew Point, which is a measure of the actual available moisture in the air, and presumably the amount of water available to soak into a guitar, and is derived from temp and RH and specifically accounts for lower water density in colder air.
My hope was that with dewpoint I could make a sliding scale that would allow me to balance a colder temperature with a higher RH and still get the same dew point, making the shop air still good for guitars, but more in line with how people actually live here.
I made the scale, and found that the recommended temp and RH represents a dew point of 49.5F. Using that, I found that at, say 68F (a common number indoors in the US in winter) you can have RH of 52% and still be the right amount of ambient moisture for a guitar. But on the other side, when it’s 80 degrees in your shop (hopefully never) you’d need to maintain RH of 32% to get the same level of raw moisture in the air. These aren’t huge numbers, but if you live in an area that’s a little more extreme seasonally you could see a significant change in your RH target.
Obviously nobody keeps their shop in the absolute Goldilocks zone all the time, but if you struggle to bring humidity down or keep your heat up, you might be able to cut yourself a small break, and you might be able to give a customer a better target humidity based on how warm/cool they keep their house. Am I completely wrong in all this?
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4 Replies
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Maybe ask other Ireland luths? @gerryhayes
Maybe your shop should be somewhat dryer than the dryest that your customers homes would be?
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I definitely intend to follow up to see how much a problem over-humidity even is here. I’m mostly just interested to know if anybody thinks I’m way off base with using a target dewpoint to figure optimal temperature or RH. It makes sense to me, but then if that were the only measure of truth the world would be VERY different.
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It’s possible that I’m under-thinking this but I generally keep my workshop around 45% RH. I run a dehumidifier that snaps on automatically if humidity gets above this. Because the dehumidifier kicks in as needed, I don’t spend any time thinking about dew points. And, as for temperature, in the winter, I try to keep it around a comfortable 20ºC (68F) while I’m working there and I’m ok to let it fall to low teens (C) during the night unless I’ve got some work that I feel is particularly temperature-sensitive. The temperature is monitored to heat as needed to maintain across the day/night.
Our climate is (as far as I remember) high 70s or low 80s RH pretty much all year around. I don’t see a lot of dry instruments. Some houses can get dry inside during winter (depending on a bundle of factors) but most instruments are not too dry here.
I’d say that the majority of Irish players don’t think about humidity (and for the most part, they can get away without doing so). For those that do think about it, the main thing I have to do is tell them they probably don’t need that humidifier in their soundhole. The advice I generally give to musicians is to buy a few cheap hygrometers, leave them in the places their guitars live and keep an eye on it. If they agree to do that, I’m happy. I can’t imagine having to discuss dew points with them. 😄
Like I say, maybe I’m under-thinking this. If a dew point calculation works best for you, go for it. It’s worth remembering that most players here probably aren’t losing sleep over it though.
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Thanks a lot, Gerry. I figured that I was probably overthinking, so it’s nice to get some more practical thoughts on the matter. After posting I wondered if I weren’t more likely to encounter musty instruments that were put away in a damp shed for ages than dried-out ones. Sounds like there’s not an epidemic of too-moist guitars either, so I guess I’ll just do what I did in the US, which is basically what you do here. Mind the temperature up to a point, and try to keep the humidity in a reasonable zone.
In case you were wondering, though, at 20C you could keep the shop at 52% RH and be spot-on, according to the Dew Point calculations. Save a little runtime on your dehumidifier, maybe.
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