Sizing Calculator
Enter your crawl space dimensions and conditions. This gives you a recommended capacity range, not a single number — real sizing has a range because two identical square-footage spaces in different climates and conditions need different capacity.
How this calculator works
This is an engineering estimate, not a substitute for a professional moisture assessment — treat the result as a starting range for comparing units, not a guarantee.
- Volume: area × ceiling height gives crawl space volume in cubic feet.
- Base rate by climate zone: we use your zone's risk classification (from our climate-zone dataset — see theclimate zone guides) as a proxy for moisture load, since that's a real regional data point rather than a subjective "how damp does it feel" guess: severe zones use 3.0 pints/day per 1,000 cu ft, moderate zones use 2.0, low-risk zones use 1.2.
- Vapor barrier modifier: −20% — a soil-covering vapor barrier measurably cuts moisture migrating up from the ground.
- Standing water modifier: +35% — a history of bulk water intrusion means periodic moisture loads well above steady-state humidity diffusion, which the base rate alone doesn't capture.
- Range: we show −15%/+25% around the computed midpoint rather than a single number, because dehumidifier capacity ratings are themselves derated in real conditions (see each review's coverage-vs-claimed discussion).