The Hub

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?