How To Buy A Dehumidifier – Part Two

In the first part of our dehumidifier buying guide, we started you out some of the basic things you need to figure out before you start checking out dehumidifier reviews and spend good money on a unit. We showed you how to figure out humidity level, air changes per hour (ACH) and how to calculate your room’s square footage. Now we are going to turn those figures into a formula that will tell you exactly what size unit you need to buy.

Calculate Your Room’s Cubic Feet

Measure the height of your room, from floor to ceiling. Now take the square footage of your room and multiple it by the height of the room to get your room’s cubic footage. For example, if your square footage is 80 feet and the height of your room is 8 feet, then your cubic footage is 640 cubic feet.

Determine Your CFM

Your CFM is the amount of airflow in cubic feet that you need in order to properly dehumidify your room. To determine this value, multiply the cubic footage of your room by the ACH and then divide by 60. For example, if your room is 640 cubic feet and your ACH is a 5, then multiply 640 by 5 and then divide by 60 (640×5=3200/60=53.3 cubic feet per minute) to get your CFM.

Determine How Much Moisture You Need To Extract From Your Room

How many pints of water you need to extract from your room depends on your ACH and your square footage. Use the guide below to determine how many pints of water you need your dehumidifier to extract from your room each day:

  • ACH 6: 16 pints per 500 square footage. For each additional 500 square feet add an additional 7 pints
  • ACH 5: 14 pints per 500 square footage. For each additional 500 square feet add an additional 6 pints
  • ACH 4: 12 pints per 500 square footage. For each additional 500 square feet add an additional 5 pints
  • ACH 3: 10 pints per 500 square footage. For each additional 500 square feet add an additional 4 pints

For example, if you have a room that is 500 square feet and you have an ACH of 6, then you need a machine that extracts 16 pints of water per day. However, if the room is 1000 square feet with an ACH of 6, then you need it to extract 23 pints per day.

Buy A Dehumidifier According To Your Specs

Now you need to find a dehumidifier that supports both your CFM requirements as well as your pints per day requirements. Make sure you read the specs of the dehumidifier you are thinking of buying to make sure that it fits your needs. However, there are a few other things you might need to consider before buying your unit. One, if your CFM requirements are much higher than any dehumidifier on the market, then you will probably have to buy multiple units to properly dehumidify your room. Two, if you CFM falls between the ranges of two different models, then you might want to buy a unit with a higher CFM and just run it less often.

This concludes our two-part article on buying a dehumidifier. I know that it might seem like there are a lot of steps and that it might take a bit of time to determine ACH, CFM and pints per day, but trust me it is worth the effort. You don’t want to buy a unit that isn’t capable of dehumidifying your room properly, but you also don’t want to buy a bigger unit (or more units than you need). By taking the time to follow these steps, you can make sure you buy the best dehumidifier for your particular needs.


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