Follow These 6 Steps to Determine the Correct Size Dehumidifier for Your Crawlspace

COMPACT $789 Purchase Crawlspace Dehumidifiers

PLUS $1197 Purchase Crawlspace Dehumidifiers

There are two sizes of Dri-CrawlSpace® Dehumidifier available.  Most crawlspaces can be guaranteed to maintain proper humidity using one or the other, or sometimes a combination of two units.

Click on a step below to see details or simply scroll down.

Determine Humidity Level Determine Air Changes per Hour Measure and Calculate Your Cubic Feet Calculate your Required Airflow Determine Minimum Dehumidification Capacity Choose Dehumidifier based on Airflow and Capacity

Be careful to NOT undersize.  If your dehumidifier is not powerful enough, it will work too hard to maintain the desired humidity level and drastically increase your electric bill.  To be sure your dehumidifier works efficiently, it is best to slightly oversize the unit for your crawlspace.

Click on these links or scroll down to see more helpful information…

• Tips for Sizing and Choosing a Dehumidifier
• Explanations of Terms Used in Sizing a Dehumidifier

By the way, take a moment to sign up to receive a FREE REPORT sent directly to your email that will reveal 7 Things You Need to Know Before You Buy Any Crawlspace Dehumidifier.

 

STEP 1.)  Determine Humidity Level

Before you chose a crawlspace dehumidifier, you must first assess the situation and determine the level of dampness in your crawlspace.  Since most people do not have a hygrometer, we have simplified humidity to 4 levels of dampness. These four levels of dampness are used to determine how much moisture is present, that must be removed:

Humidity Level	Crawlspace Characteristics
Moderately Damp	Crawlspace feels damp and smells musty in humid weather.  This is most common for normal crawlspaces that have no visible water source.
Very Damp	Crawlspace area always feels damp and smells of mildew, moisture spots on walls and floor.  If you have a hot water heater in your crawlspace, you can consider your space very damp.
Wet	Crawlspace feels and smells wet.  Leakage visible, mold and mildew present on surfaces.  Crawlspaces that are not totally enclosed can go in this category.
Extremely Wet	Crawlspace area has standing water present, or is waterfront property.

To help you accurately determine your moisture or humidity level, consider the environment around your house.  Is it often rainy?  Do you live near water?  Here is a map showing humidity for the United States.  Click the humidity map to see current humidity conditions.

 

STEP 2.)  Determine Air Changes per Hour

Next, take your dampness or humidity level to find your required number of air changes per hour (ACH).  Remember this number, you will need it in the CFM formula further below.

Moderately Damp	Very Damp	Wet	Extremely Wet
3 Air Changes	4 Air Changes	5 Air Changes	6 Air Changes

 

STEP 3.)  Measure and Calculate Your Cubic Feet

Determine the cubic feet of your crawlspace.  Take the length multiplied by the width multiplied by the height.  If there are multiple areas or rooms, you need to consider if the air can freely flow between them.  Separate areas may need to be addressed separately with their own dehumidifier.  But, if the areas are open to each other and air can freely flow between them, simply add the areas together.

 

STEP 4.)  Calculate Your Required Airflow

You will need your Cubic Feet and Air Changes number to determine Airflow.  Airflow is measured in cubic feet per minute (CFM).  Simply use the formula below to find the CFM you need for your crawlspace.

 

STEP 5.)  Determine Minimum Dehumidification Capacity

The following chart provides a helpful reference for finding your minimum dehumidification capacity needed for your crawlspace.  You should remember that this chart is a guide for general purposes and that there are many variables in dehumidification such as climate, number of occupants, number of moisture producing appliances and the number of windows and doors you have.  To talk to a technician about your crawlspace issues, call 1-800-564-0667.

Area to Dry	Dehumidification Required - Pints Per Day
Square Feet	Moderately Damp	Very Damp	Wet	Extremely Wet
500	10	12	14	16
1,000	14	17	20	23
1,500	18	22	26	30
2,000	22	27	32	37
2,500	26	32	38	44
3,000	30	37	44	51

 

 

STEP 6.)  Choose Dehumidifier Based on Airflow and Capacity

The final step is finding equipment that matches your requirements.  We designed the Dri-CrawlSpace^® Dehumidifiers in two sizes.  One or the other, or a combination of the two units can accommodate any residential or commercial crawlspace application.  As you can see from the table below, the Dri-CrawlSpace^® COMPACT will handle the requirements of our example (which needs 14 Pints/Day and 135 CFM) with some additional capacity to handle situations when you may have an unusually humid or rainy stretch of weather.  

Model	CFM	Pints/Day	Price
Dri-CrawlSpace® COMPACT	200	35	$789 Purchase Crawlspace Dehumidifiers
Dri-CrawlSpace® PLUS	350	50	$1197 Purchase Crawlspace Dehumidifiers

Remember, the two reasons you should use a dehumidifier is to protect your home and your health.  A properly sized and installed crawlspace dehumidifier, along with a vapor barrier, effectively helps to prevent mold, metal rusting, and the swelling of doors, wall panels and floors.  Keeping the indoor air moisture level low also helps deter dust mites and other allergens that thrive in humid conditions.

To insure that your dehumidifier removes as many pints of moisture as it claims, the Association of Home Appliance Manufacturers (AHAM) licenses U.S. manufacturers and private-brand sellers to certify, under the AHAM program, the water removal capacity rating and energy factors of dehumidifiers sold in the United States.  AHAM requires the water removal capacity be verified through independent laboratories using the American National Standards Institute (ANSI) test method.

Tips For Sizing and Choosing a Dehumidifier

If you are having difficulty calculating the amount of humidity in your crawlspace or house, you can buy a hygrometer.  A hygrometer is an inexpensive instrument used to measure relative humidity. When you have found a dehumidifier with the correct water removal capacity for your crawlspace, be sure to check for some other useful features: Installation Size - make sure your unit is small enough to fit throug your crawlspace entrance and short enough to fit in the crawlspace when raised off the ground Operating Temperature - make sure your crawlspace dehumidifier can operate in all seasons Drainage - because your dehumidifier is located in your crawlspace, avoid dehumidifiers with drain pans to empty, use units that have drain lines that will keep the water away from your crawlspace Another important consideration when installing your crawlspace dehumidifier is safety.  Make sure your dehumidifier is plugged into a properly grounded outlet.  Clean filters yearly and always follow all manufacturers’ instructions to insure safe and effective operation.

 

Explanations of Terms Used in Sizing a Dehumidifier

Dehumidifier Capacity - Pints Per Day (PPD) Dehumidifiers are rated by the maximum amount of moisture they will remove from the air in a twenty-four hour period.  This rating is measured in pints.  The capacity of a dehumidifier is expressed in pints of water condensed in 24 hours at 80 degrees and 60% relative humidity.  This capacity is often shown as "Pints/Day - 80°F@60%", or sometimes just "Pints".  The temperature, 80°F and RH level of 60% is a standard benchmark used by AHAM (Association of Home Appliance Manufacturers) and Energy Star. Airflow - Cubic Feet Per Minute (CFM) A lesser known, yet very important capacity for dehumidifiers and any air treatment equipment is Airflow Rate.  This is the speed the air moves through the unit, measured in CFM, cubic feet per minute.  It basically tells you how powerful the fan is.   Every dehumidifier has a fan that pulls the air through the unit.  Generally speaking, higher CFM means the air in your crawlspace will be dehumidified faster. Relative Humidity (% RH) When dealing with moisture issues, many people hear the terms relative humidity and dew point without fully grasping what they mean.  Relative humidity (RH) is the term most used to describe the percentage of water vapor that exists in a gaseous mixture of air and water.  A RH reading is a measure of the amount of water vapor present in the air compared with the amount of water the air can hold at the temperature at the time of measurement.  Relative humidity is expressed as a percentage and is calculated as follows: Relative Humidity = actual vapor density  x 100% saturation vapor density In plain English, the RH level tells you the percentage of water in the air.  When relative humidity is 100%, water vapor in the air will turn into rain, condensation, dew, snow or frost.  You can feel relative humidity on your skin because it is a measure of how much water vapor the air can hold before it turns to liquid. Relative humidity is affected by temperature.  As temperature becomes colder, relative humidity will raise.  Relative humidity in a room may be 50%, but when you introduce a cold glass of water, the air around the glass gets cold and condensation forms on the cold surfaces.  What happens here is that relative humidity of air contacting the cold surfaces raises from 50% to 100% as water vapor turns to liquid. Dew Point (Degrees) Dew point is the temperature at which water vapor condenses into liquid.  The dew point indirectly indicates a measure of how much water vapor there actually is in the air.