Crawlspace Moisture
If you have a musty smell, visible mold, or a persistently damp floor near a crawlspace and haven't diagnosed why yet, this is the mechanism -- not a product pitch. Once you understand what's happening, the right next step (measure, then choose a dehumidifier or absorber) is below.
Where the moisture actually comes from
Soil under a house holds moisture year-round. Without a sealed vapor barrier laid directly over that soil, water vapor evaporates straight into the crawlspace air. From there it migrates upward into the subfloor and the living space above -- which is why a crawlspace problem often shows up as a musty smell or damp flooring one level up, not just as visible dampness in the crawlspace itself.
Standing water or a failed barrier needs a contractor first
If there's standing water, a visibly torn or missing vapor barrier, or active mold growth beyond a small surface patch, that's a structural repair job -- a dehumidifier or absorber placed on top of an unfixed source will run constantly without solving the underlying problem.
Next: measure, then choose
Get an actual reading with a hygrometer, then use this decision page to pick between a dehumidifier and a moisture absorber -- a smaller or vented crawlspace-adjacent space may not need full dehumidification at all.
This is basement-adjacent territory -- see Best Dehumidifier for Basement if the affected space is specifically a basement rather than a crawlspace.