When an open or ventilated drying system is inappropriate, a closed drying system using mechanical dehumidification equipment should be used. Certain minimum dehumidification capacities are appropriate for most closed drying systems.
The IICRC recommendations for initial dehumidifier capacities listed below should be considered, along with other factors including professional judgment, when making decisions about how much equipment is needed. After the initial installation, appropriate adjustments in dehumidification equipment capacity are made based on changes in environmental conditions, such as temperature, RH, SH and material moisture content. Initial dehumidifier capacity requirements are calculated using the formula discussed below:
- Step 1: Calculate the cubic feet (ft) of air in the area being dried by multiplying its length x width x height.
- Step 2: Determine the Class of the water-damaged environment.
- Step 3: Using the IICRC initial dehumidification capacity table below, select an appropriate divisor and calculate the minimum dehumidification capacity required for initial setup of a closed drying system, by dividing the divisor into the cubic footage of the area being dried. This yields the total number of pints of dehumidification capacity needed; i.e., AHAM-rated pints that should be removed from that area every 24 hours to achieve effective drying.
- Step 4: Using the Association of Home Appliance Manufacturers (AHAM) specifications regarding the dehumidification capacity of specific equipment, calculate the number or size of dehumidifiers required. Dehumidification capacity for refrigerant dehumidifiers is expressed in pints of water removed in 24 hours at AHAM-designated conditions of 80°F (27°C) 60% RH (pints per day, or ppd @ AHAM test specifications). This ppd @ AHAM rating is available from the refrigerant dehumidifier manufacturer. Dehumidification capacity for desiccant dehumidifiers is expressed in cubic feet per minute (cfm) of air processed
Initially, effective drying of structural materials requires that air in a structure be exchanged based on the dehumidifier’s ability to remove a specific number of pints per day. On-going equipment use is based on psychrometric calculations to verify adequate and safe drying.