The IICRC WRT body of knowledge provides guidance for initial LGR dehumidification capacity based on cubic footage and class of water. For Class 3 intrusions, which involve the greatest amount of moisture absorption and evaporation (excluding Class 4), a higher dehumidification capacity is required.
A commonly taught WRT guideline is approximately one LGR dehumidifier (≈150 PPD) per 3,000 cubic feet for Class 3 conditions. Applying this to a 9,000 cubic foot drying chamber results in a total recommended capacity of approximately 450 PPD.
This capacity ensures that evaporated moisture is removed efficiently, preventing elevated humidity and secondary damage. The WRT curriculum emphasizes that insufficient dehumidification in Class 3 losses can stall drying and increase microbial risk.
As with all equipment recommendations, this is an initial placement subject to adjustment based on monitoring data, but 450 PPD represents the correct starting capacity under WRT guidance.
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