Out of sight, out of mind. If you have this attitude toward the air quality in the crawl space under your house then you’re heading for trouble.
Choosing the best crawl space dehumidifier to ensure a mold and damp free crawl space can save you a lot of money, hassle and health problems.
Mold spores are constantly in the air just looking for an ideal spot to start growing. If the inside of your house is heated and the humidity level is kept below 60% then you won’t give mold a chance.
The crawl space under your house is a bigger challenge though. The high levels of moisture in the ground beneath the crawl space will quickly result in mold growth if you don’t get rid of that moist air with an under house dehumidifier.
Besides the damage this can eventually do to the underside of your house there are health implications as well.
If your house is heated then the air inside rises up and results in air being drawn into the house from the crawl space.
Along with that air comes the spores and other nasties that cause allergies and other respiratory problems. Your best bet to combat this is to use a dehumidifier or a decent fan with a humidistat.
There are some indoor commercial units listed in our dehumidifier reviews that could work in certain crawl space applications.
That's if you could get them to fit. The crawl space is generally too small to fit these units in so that's why the smaller, purpose made dehumidifiers are generally used in these spaces. Because they’ve tried to pack more punch into a smaller space these products can get a bit pricier than the bigger general purpose units.
Crawl space fans with a humidistat can also be an effective solution if the humidity of the air outside the crawl space is low enough. For really humid and damp environments a fan alone just won’t cut it though. Check out our top rated choices in these fan and crawl space dehumidifier reviews.
Crawl Space Dehumidifier Comparison Table
Air Movement (CFM)
12 x 12 x 21
15.75 x 23.6 x 13.5
12 x 14 x 22
18 x 9 x 2
8.7 x 11.8 x 6.1
Top 5 Crawl Space Dehumidifiers Reviews
Sante Fe specialize in dehumidifiers for crawl space applications and this is our favorite.
This is a really powerful and extremely compact unit. It's only 12"x12" so it will fit into most crawl spaces.
It will remove up to 70 pints per day and is ideal for crawl spaces of up to 1,800 square feet.
Power consumption is always a concern when purchasing this type of product so we really liked that this unit is Energy Star rated.
If you live in a warm climate then low temperature operation isn't a real concern but if you often experience cold temperatures then your options are limited.
This unit is capable of low-temperature operation and will work down to 49 degrees.
It also has an auto-restart function so you won't have to turn it on again after a power failure. It's easy to see why this product gets so many great reviews.
Ebac make great dehumidifiers and for crawl space applications this is one of our favorites.
It will remove up to 56 pints per day which is plenty for most crawl space conditions.
It’s built rock solid and the interior is galvanised steel so you don’t need to worry about rust.
The adjustable humidistat is easy to set and read. While some units run continuously the CD85 will cycle on and off to maintain the desired humidity.
It also has a built-in discharge pump which makes continuous discharge operation possible even if you need to run the hose out through a space that’s higher than the unit.
It’s got a powerful fan that will shift plenty of air and is effective in spaces of up to 8,000 cubic feet.
If you’re looking for a really compact unit to fit into a tight crawl space then this is a great option.
If you have a big crawl space then one of the units above are your best bet but this product is great for smaller crawl spaces.
The CD30E comes with a wall mount and installation kit and is easy to install.
Like the CD30 it delivers exceptional performance but the “E” in this model number refers to the electronic controller that allows you to set the humidity level you want.
This unit is energy efficient and will switch itself off when the right humidity level is reached.
Although it’s compact it will remove 17 pints per day and is effective in spaces up to 3,000 cubic feet. It also has an alarm that will let you know if the humidity rises to undesirable levels.
Sometimes all you need is a good fan with a built-in humidistat. That’s exactly what Durablow have put together in this product.
The Stainless Steel construction makes for a durable product that you’ll never have to worry about. The dual fans shift a combined total of 220 cubic feet per minute.
The adjustable humidistat means that they will cycle on and off to maintain the level of humidity you set it to.
So there’s no need to worry that the fans will stay on all the time and run up your electricity bill.
While it isn’t as effective as a dehumidifier, replacing the humid air inside the crawl space with dry air from outside will sort out a lot of damp and mold problems.
Tjernlund have a long history of producing top heating and ventilation products. This dual fan crawl space ventilator is a top quality product with great performance.
Like the Durablow unit we reviewed above, the dual fans combine to move 220 cubic feet per minute.
It comes with an adjustable humidistat that will switch the fans on and off to regulate the humidity.
To protect the fans it also comes with a freeze protection thermostat.
If the air temperature goes below 35°F then the unit won’t operate. Once the air temperature gets up to around 50°F the thermostat will allow the unit to turn on again.
Here is a summary of the factors you need to consider before making your purchase:
Dehumidifier size - Does the dehumidifier have the capacity required for the volume and humidity level of the crawl space? Check out our sizing guide below.
Temperature - Will the crawl space regularly experience cold temperatures? If so then make sure the unit you buy supports low-temperature operation.
Crawl space moisture level - How much humidity is the unit capable of extracting per day?
Airflow - Does the dehumidifier have a decent fan to circulate the air effectively? The bigger the volume of your crawl space, the higher the CFM (Cubic Feet per Minute) airflow spec you will need. More on that below.
Energy efficiency - How much electricity is this thing going to use? Make sure you get a product that cycles on and off around your humidity setpoint. If you get an Energy Star rated product then you will end up paying less on your electricity bill.
Crawl Space Preparation
First let’s talk about the things you need to do to your crawl space before you even install a dehumidifier.
The best way to prevent humid air getting into the crawl space is to seal it. Seal up any openings to the crawl space and you’re halfway there. It’s a good idea to also isolate the crawl space from the dirt floor.
Create a vapor barrier by using a plastic sheet about 4 mil thick to cover the floor and seal the plastic sheet part way up the walls of the crawl space.
Now you’re ready to install the dehumidifier.
What Size Dehumidifier Do I Need For My Crawl Space?
The dehumidifier you need depends on the volume of the space and the level of humidity.
To calculate your crawl space volume you multiply the length by the width and then multiply that by the height of the crawl space (length x width x height) to get the volume in cubic feet.
The next thing to determine is how humid the space is. This will determine the Air Changes per Hour (ACH) required in our calculation.
This is a measure of how many times all the air in the crawl space needs to move through the dehumidifier per hour.
Use the following table that uses Relative Humidity (RH) to determine the required ACH:
Relative Humidity (RH)
Air Changes Per Hour (ACH)
60% - 70%
70% - 80%
80% - 90%
90% - 100%
Once you’ve determined the ACH then it’s time to pull out your calculator again. Multiply the volume of the space (cubic feet) by the ACH and then divide the result by 60.
This will give you the required airflow in CFM or cubic feet per minute. When you choose your dehumidifier make sure its fan is capable of shifting this amount of air.
We've also put together a more detailed post if you want to know what size dehumidifier to get.
Crawl Space Moisture Level - What Capacity Do I Need?
Once you know that the dehumidifier has a fan capable of giving you the CFM you need it’s time to make sure it can also extract enough humidity out of the air.
The table below uses the area of the crawl space (not volume) and the RH to indicate the capacity, in pints per day, that you need.
Pints Per Day
Temperature of Crawl Space
The lower the temperature the less effective a dehumidifier becomes. If the coils freeze up then the compressor won’t come on at all. Make sure that you choose a dehumidifier with hot gas defrost function.
This means that the dehumidifier is capable of producing hot air to blow over frozen coils to defrost them. This is especially important if your crawl space experiences temperatures close to freezing.
Bear in mind that once the temperature gets down to below 40 degrees compressor type dehumidifiers are going to be pretty useless.
Even if they claim low temperature operation it just means that it will work down to a little above 40 degrees.
Make sure that the dehumidifier you buy is Energy Star rated. Just because a dehumidifier uses very little electricity doesn’t make it effective.
Also, having a dehumidifier that works really well but uses a bunch of electricity isn’t great either. If a dehumidifier is Energy Star compliant it means that it extracts a good amount of humidity while using a reasonable amount of electricity.
The energy efficiency of a dehumidifier is measured in liters of water removed per kilowatt-hour of energy consumed.
The Energy Star guidelines have a target of somewhere between 1.2 and 2.25 Liters for every kilowatt/hour consumed.
If you take the above into consideration and buy one of the products we reviewed above then you’re on your way to a damp and mold free crawl space.
Do the calculations properly and check them twice before making your purchase. Don’t take shortcuts by trying to avoid the sealing of the area.
If you do this and if you buy one of the best crawl space dehumidifiers like the ones above then you’ll have peace of mind for years to come.
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