On a Class 4 water intrusion that is 2,000 square feet with an 8-foot ceiling...

The IICRC WRT body of knowledge explains that Class 4 water intrusions involve deeply held or bound water and typically require specialized drying methods, including desiccant dehumidification. Initial desiccant sizing is based on cubic footage and airflow capacity rather than AHAM pints.

In this scenario, the affected volume is 2,000 square feet × 8 feet = 16,000 cubic feet. A common WRT starting guideline for desiccant systems is approximately one 400 CFM desiccant unit per 8,000 cubic feet for Class 4 conditions.

Dividing 16,000 cubic feet by 8,000 cubic feet per unit results in an initial recommendation of two 400 CFM desiccant dehumidifiers. This capacity provides sufficient airflow and moisture adsorption to manage the heavy moisture load typical of Class 4 losses.

The WRT manual stresses that this is an initial recommendation and must be validated through psychrometric monitoring and material moisture readings. Desiccant systems are often adjusted as drying progresses.