Dehumidifiers are a great tool to use when your business has suffered from water damage. When assessing the damage, it can be overwhelming to determine what type of dehumidifier you will need and how many dehumidifiers you will need. Here are six steps to help you determine what size dehumidifier you will need and how many dehumidifiers you will need to eliminate the water from your home or business.

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  1. Assess the damage and moisture levels. Do you have a slightly damp carpeted area, maybe a little moisture in your drywall, or are you dealing with puddles of standing water?
  1. Determine where you can rent the needed equipment. Find a rental company that can accommodate you with industrial strength dehumidification units as well as supplemental air movers or fans.
  1. Work with a technical or sales representative. Technical/sales representatives can help you calculate what type of units you’ll need, how many, and how strong they’ll need to be.  Do not assume stronger and faster is better. Depending on the severity of the damage and levels of moisture, drying things out too quickly can result in cracked drywall or other complications.
  1. How many air changes do you need? Dehumidification units typically refer to the number of “air changes” they complete per hour, which is simply how many times the room’s ambient air is processed through the machine per hour. A good rule of thumb is to start at 6 air changes per hour and go down from there depending on the severity of the water damage.
  • Six air changes per hour would be for a very wet environment, such as a room with standing water, visibly soaked drywall, etc. Keep in mind, if the water damage is this bad, a total or at least partial replacement of the drywall in the room will probably be necessary.
  • Five air changes per hour are needed when there is slightly less water, but the room is still very wet. You may still need to consider additional drywall replacement.
  • Four air changes per hour would be needed for a very damp, but not totally soaked through room.
  • Three air changes per hour would be necessary for a room that is moderately wet/damp. You will be able to feel slight moisture in the carpet or drywall to the touch, but will not see any water seeping through.
  • Two or one air changes per hour would be for anything less serious than the above scenarios.
  1. How much air needs to be processed? Now you will need to determine the amount of air that will need to be processed, a.k.a. cubic feet of air per minute (CFM).  In order to determine the CFM, start by determining the cubic feet of the room being treated. You can do this by multiplying the room’s length by the width and height (LxWxH).
  1. Use your CFM to determine how many dehumidifiers you need. Multiply the cubic feet of the room by the number of air changes needed per hour, then divide that number by 60. Now you’ve got your CFM and can pick out how many dehumidification units you’ll need. A good rental company will have a decent assortment of CFM ranges. Portable Air has dehumidifiers that range from 160 to 400 CFM.

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Here is a quick example to put all of the above information together: If you have a room that is 10,000 cubic feet with moderate water damage, you will need around 3 air changes per hour. So, that’s 10,000×3 = 30,000. Divide 30,000 by 60 = 500. Now you know that you will need at least 500 CFM of dehumidification in that room to get the desired effect. Therefore, based on the above example, a 400 CFM unit and a 160 CFM unit working together would be a great option.

For more information on dehumidifiers and determining how many units you will need to combat water damage, visit or call 800-341-4297.