How do you determine how many and what size dehumidifiers to use on a water damage job?

Started by Amy , July 7, 2021
5 (2)

Water Damage Restoration Commercial restoration

To determine the number and size of dehumidifiers for a drying project, you must first calculate the cubic volume (length × width × height) of the space involved.

Then remove any materials that will not be dried. This includes items that are to be discarded (because they are contaminated or badly damaged) or delicate or valuable items that could be damaged by the drying process.

Now determine the class of water loss. Classes of water loss describe the potential evaporation rate of the materials involved. 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 short, Class 1 involves less than 5 percent of the surface area; Class 2, between 5 and 40 percent; and Class 3, more than 40 percent. Class 4 materials are typically dense materials that are saturated with water.

As mentioned earlier, each class has been assigned a factor. We divide the cubic feet by the assigned factor for the class and the type of dehumidifier being used. This calculation yields the minimum number of AHAM pints required for effective drying.

The capacity of low refrigerant dehumidifiers using conventional refrigerant 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 these conditions is commonly referred to as the AHAM rating. To determine the number of dehumidifiers needed, divide the number of pints required to dry the space by the capacity of your dehumidifier (if you do not know the AHAM rating of your dehumidifier, check the manufacturer's website). The result of this calculation will indicate the number of units needed. Always round up when giving this answer. Dehumidifiers do not work well if they are cut in half! 

David, Director of Restoration at CADPXS Brands, has over 35 years of experience in the restoration industry. He has worked on restoration projects throughout the United States, Canada and the Caribbean and now teaches smoke and water damage restoration courses for CADPXS Brands throughout North America.

(888) 928-1380 (Monday-Friday: 08:00AM - 5:00PM) UTC Email:

2 Reviews 5 (2)
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Communication level 5
Recommend to a friend 5
Communication level 5

Mariah Bennett 5
United States

Using a suitable dehumidifier saves our equipment costs. You can imagine that if the dehumidification capacity of the equipment you use is too small, you must buy one or more. When the dehumidification capacity of your dehumidifier is too large, the equipment function will be very Big waste.

Published on 2021-07-07 15:55:36

Cole Warren 5
United States

Dehumidifiers are not as powerful as possible, because bigger usually means higher noise levels. In many cases, two small dehumidifiers are more effective than large dehumidifiers of the same power, because two smaller dehumidifiers can more effectively drive the airflow and improve the efficiency of dehumidification.

Published on 2021-07-17 14:30:40

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