Find the Source of Crawl Space Moisture
A musty smell is a reason to investigate moisture, not enough information to identify the source. Look for a pattern before choosing a fan, liner or dehumidifier.
Separate water entry from humid air
Note whether the problem follows rain, appears near plumbing or occurs during humid weather. From a safe access point, look for wet soil, damaged ground covering, pipe leaks, condensate discharge and damp framing. Outside, check where roof runoff goes.
Do not enter standing water or a space with damaged wiring or unsafe framing. Those conditions need professional assessment first.
Measure air humidity and track the pattern
A hygrometer measures relative humidity in the air. A material moisture meter answers a different question about a surface or building material. Record humidity, temperature, location and recent weather so readings can be compared.
EPA recommends indoor humidity below 60%, ideally 30–50% when possible. A single air reading does not show whether concealed wood is dry or prove that mold is absent.
Resolve the cause of a persistent smell
Repair the moisture source and address affected materials. Fragrance or a lower dehumidifier setting does not remove existing contamination. Persistent odor, hidden damage or a larger mold problem is a reason to involve an experienced remediation professional.
Your next step
Keep a short log of rain, odor and humidity. Take photos from a safe location and use the pattern to describe the problem when requesting help.