Protecting Your Property with Proper Dehumidification
Excess moisture in enclosed spaces like crawl spaces, basements, and indoor grow rooms is the primary catalyst for mold growth, wood rot, and structural degradation. Our Dehumidifier Sizing Calculator uses psychrometric load estimates to determine the exact moisture removal capacity (Pints Per Day) your space requires to remain safe and dry.
Understanding Pints Per Day (PPD) and AHAM Ratings
Dehumidifiers are rated by their moisture removal capacity in Pints Per Day (PPD). The industry standard, established by AHAM (Association of Home Appliance Manufacturers), tests this capacity at 80°F and 60% Relative Humidity. When selecting a unit, it is crucial to use the AHAM rating rather than “saturation” ratings (tested at 90°F/90% RH), which artificially inflate performance numbers.
The Danger of High Humidity in Crawl Spaces
Crawl spaces are notorious for trapping moisture evaporating from the exposed dirt floor. When the relative humidity exceeds 60%, airborne mold spores begin to germinate on the floor joists and subflooring. Over time, this leads to wood decay and compromised structural integrity. Furthermore, up to 50% of the air on your first floor comes directly from the crawl space via the “stack effect,” meaning crawl space mold directly impacts your indoor air quality.
Commercial vs. Residential Dehumidifiers
While a $200 residential dehumidifier from a big-box store might work for a small bedroom, it will fail rapidly in a harsh crawl space environment. Commercial-grade units, such as the Argendon Sandidry Pro series, feature:
- Epoxy-Coated Coils: Protects against corrosive freon leaks.
- High CFM Blowers: Circulates air rapidly across large footprints.
- Built-in Condensate Pumps: Automatically pushes collected water vertically and outside, eliminating the need to empty buckets.
- Hot Gas Defrost: Allows the unit to operate in temperatures down to 36°F without freezing the evaporator coils.
Setting the Target Humidity
For optimal preservation of building materials and total inhibition of mold growth, target a relative humidity setpoint of 50%. Lowering the humidity further (e.g., to 40%) provides little additional benefit but drastically increases the energy consumption and runtime of your dehumidifier.
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Data-driven soil, irrigation, and yard automation calculators developed in accordance with university agricultural extension standards and empirical field testing.
Frequently asked questions
What is the difference between AHAM PPD and Saturation PPD ratings?
AHAM rating measures moisture extraction under realistic operating conditions of 80°F (26.7°C) and 60% Relative Humidity. Saturation rating measures extreme laboratory conditions of 90°F (32.2°C) and 90% RH, inflating PPD numbers by roughly 80%. Always size equipment by AHAM standards.
Why is a commercial crawl space dehumidifier required even with a vapor barrier?
While a 12 to 20 mil plastic vapor barrier prevents direct bulk soil water evaporation, exterior humidity still infiltrates through foundation masonry walls and rim joists. Mechanical dehumidification maintains RH below 55%, preventing fungal wood rot and mold.
What airflow (CFM) is needed for subterranean crawl spaces?
Crawl space dehumidifiers should cycle total space air volume roughly 3 to 4 times per hour. A 4,800 cubic foot crawl space requires minimum continuous airflow of 240 to 320 CFM to avoid dead pockets of stagnant moist air.
Do I need a built-in condensate pump?
Yes. Most residential crawl spaces lack gravity floor drains. A commercial unit with an integrated condensate pump can lift wastewater 15 to 20 feet vertically and pump it through foundation walls to exterior discharge lines.