This reddit/Firearms thread discusses dehumidifiers and the process of trying to keep your guns from rusting.
There is some confusion in that thread and I know this comes up sometimes so I thought I would clarify this issue for readers.
Customary dehumidifiers are nothing more than strip heaters. What happens is that when sensible heat is added to air, it moves horizontally across the psychrometric chart and (a) increases the dry bulb temperature while also (b) decreasing relative humidity.
Relative humidity is not absolute humidity. The number of grains of moisture per pound of dry air doesn’t change when sensible heat is added (or even removed, as long as we stipulate not condensing moisture out of the air). Changing the relative humidity changes the amount of moisture the air can contain. At a higher temperature, the air can contain more moisture, and lower temperature lower amount of moisture.
The air contains more energy at higher temperatures and thus it’s more difficult for the moisture to condense out of the air. Try moisture removal only occurs when the air is passed across a cooling coil down to the condensation line, passing that condensate to a drain pipe (usually with a running trap that needs to be inspected at least yearly to ensure no clogging and filled with Clorox). Then when the air must be sensibly heated again, with a true reduction in absolute humidity for use in the designated space. This is what happens when you air condition your home.
![Charting the Proper Psychrometrics of Humidification and ...](https://www.esmagazine.com/ext/resources/images/2021/ES-petrus-slide1-900x550.jpg)
It isn’t usually practical to pass the air in your gun cabinet or gun safe through a cooling coil to remove moisture. The only other option for conditioning the air is to pass it over a strip heater thus changing the relative humidity, not absolute humidity.
As long as the space where your guns are located is already conditioned, i.e., your home, that’s usually not necessary. However, I do a little extra by putting desiccant in my gun safe to ensure the driest possible environment.
I don’t like the idea of a strip heat causing an increase in dry bulb temperature in my gun safe, mainly because of possible malfunctions.
If your gun safe is located in an unconditioned space like a basement, you may have to consider strip heating. The better option would be to remove your safe and put it in your home. I don’t have a safe in my garage for that very reason (and also because of possible theft).