Please ensure Javascript is enabled for purposes of website accessibility Legend Brands Restoration | How do you determine how many and what size dehumidifiers to use on a water damage job?
How do you determine how many and what size dehumidifiers to use on a water damage job?
To determine the number and size of dehumidifiers to place on a drying project you must first calculate the cubic volume (length × width × height) of the affected space.

Next, remove any materials that will not be dried. This includes objects that are slated for disposal (because they are contaminated or extensively damaged) or delicate or valuable items that might be damaged by the drying process.

Now determine the class of the water loss. Classes of water loss describes the potential evaporation rate of the affected materials. There are four classes of water loss. Each class has a factor that indicates the number of cubic feet that can be dried per pint of dehumidifier capacity. In brief, Class 1 has less than 5 percent of surface area affected, Class 2 has between 5 and 40 percent surfaces involved, and Class 3 has more than 40 percent. Class 4 materials are typically dense materials that have been saturated with water. 

As mentioned, each class has been assigned a factor. We divide the cubic feet by the assigned factor for the class and type of dehumidifier being used. This calculation indicates the minimum number of AHAM pints required to effectively dry.

Low grain refrigerant and conventional refrigerant dehumidifier capacity is determined by placing a dehumidifier in a controlled chamber. 80 degrees and 60% relative humidity are maintained for 24 hours. The number of pints of water removed from the chamber under those conditions is commonly described as the AHAM rating. To determine the number of dehumidifiers that are required, divide the number of pints required to dry the space and then divide by your dehumidifier capacity (if you do not the AHAM rating of your dehumidifier, check the manufacturers website). The result of this calculation represents the number of machines needed. For this answer, always round up. Dehumidifiers do not work well when they are cut in half!    
Bill Weigand, Director of Restoration Chemicals for Legend Brands, has over 35 years of experience in the restoration industry. He has worked on disaster restoration projects in the United States, Canada and the Caribbean, and now teaches IICRC-certified smoke and water damage restoration courses for Legend Brands across North America.