Confused about humidity levels in basement - a math problem
Your basement is not nearly as sealed as you think. Which is actually a good thing.
You need to constantly have make up air. That is air to replace the air you breathe. Otherwise, while your H2O is going down (thanks to the dehumidifier), your O2 is also going down and your CO2 is going up as you breathe. I am not going to do the math, but just think &quot;Apollo 13&quot;.
End result, even a relatively well sealed basement (or any other room or entire house) has quite a bit of air moving in and out all day long. Yes, we want to minimize it to keep heating &amp; cooling costs down, but it is nowhere near zero. So some fresh air comes in, with more humidity and some old air goes out. All day long. Plus if there are people or pets around then they will add to the humidity with every breath. Plus, depending on the permeability of the basement walls, you may get some moisture coming in from the ground as well.