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Crawl Space and Basement Dehumidification

There are two kinds of dehumidifiers readily available to consumers. The easiest to find and cheapest type are appliance grade dehumidifiers. These are what you find in hardware or home appliance stores like Lowes, Home Depot, Sears, etc. These units have been around for years. They stand upright, have a water bucket to empty and cost about $200 to $400. These are designed to work in the living space of a home, NOT to be used in the crawlspace. If you try to put one in your crawlspace, it will be overworked. The result is an extremely high electric bill and a unit that freezes over and shuts down in cool weather.

A crawlspace dehumidifier is NOT something that looks like a plastic, electronic device that sits upright in your bedroom, but more like a piece of metal HVAC equipment that lays low in your crawlspace. These units are much more heavy duty and can withstand harsh temperatures and conditions found in a crawlspace.

Here are the basic specifications for a crawlspace dehumidifier:

Pints/Day, Airflow, Operating Temperatures, Weight, Size and Price

Pints-per-day tells you the capacity of water each unit can remove from the air in a 24 hour period. For some dehumidifiers, the pints/day is overkill for a crawlspace. More pints per day, generally means, bigger refrigeration coils that use more electricity. For a more efficient unit, we would prefer medium sized coils ran at a higher CFM… which leads us to Airflow.

Airflow, measured in CFM (cubic feet per minute) tells you how much air is passing through the unit as it conditions the air. The higher the CFM, the faster the air within the crawlspace becomes dehumidified. CFM is important, but more is better.

Operating temperature means little when picking out a TV, radio, room air purifier, or other home appliance, but temperature is EXTREMELY important for a crawlspace dehumidifier. Crawlspaces are generally colder than the house above. Depending on your crawlspace, the dehumidifier needs to be able to work in temperatures slightly colder than outdoor temperature. There is no need for a dehumidifier below freezing point, though mold contusive moisture conditions usually run rampant during cold rainy weather all the way down to the mid 30s.

These are commercial type products designed to operate under a much wider range of temperature and humidity than residential dehumidifiers.

By Dehumidifying the Crawl Space you lower the humidity that causes mold, allergies, wood rot and the moisture condition that invites rodents, dust mites and insect infestations.

Crawl Space COMPACT
Crawlspace Dehumidifier

Electrical 115V/60Hz/3.5A
Airflow 200 CFM
Weight 60 lbs
Refrigerant R-410a
Operating Temp 33°F – 90°F
cs1 Price: $ 1,184.00
Crawl Space PLUS
Crawlspace Dehumidifier

Electrical 115V/60Hz/4.2A
Airflow 350 CFM
Weight 62 lbs
Refrigerant R-410a
Operating Temp 33°F – 90°F
 cs1 Price: $ 1,497.00
Condensate Pump
You will need this pump if your drain hose must be routed up over any obstacle.  Without the pump, the hose must always travel on a downward slope to your drain or outside.Pump plugs into standard 115V outlet. Includes mounting hardware and 20′ of drain tubing.
 cs2 Price: $123.00
Remote Humidistat
Do you need more accurate control over your relative humidity levels? This humidistat provides maximum accuracy.
Humidistat requires a dedicated outlet installed into the crawlspace. The humidistat wires in line with the lead and switches the outlet on or off according to humidity levels detected.
 cs3 Price: $132.00

First item to consider is temperature.  Most people think humidity is only a problem during hot, humid, muggy days and because of this, most dehumidifiers are built to run efficiently in hot weather.  Ordinary dehumidifiers have a difficult time operating effectively in low temperatures.  If your home feels comfortable, then where is all of this mold coming from?  It grows and reproduces in all temperatures, all year long.  Even during cold weather, when your home feels dry, high levels of relative humidity exist outside and in your crawlspace.  Because your crawlspace is always colder than your living space, relative humidity is always higher in the crawlspace.  That’s how mold manages to grow unnoticed and that’s why cold temperature operation is an important feature for crawlspace dehumidifiers.

Anytime it is raining or snowing outside, relative humidity will be at 100%.  On overcast days, though temperature is cool, humidity is high.  These are conditions when your crawlspace is most susceptible to moisture damage and mold growth.  This is when you need a dehumidifier to remove the moisture.  Moisture exists in all temperatures down to 33 degrees Fahrenheit; therefore your dehumidifier should also work in these conditions.

Higher temperatures are less critical for a crawlspace dehumidifier because the crawlspace stays pretty cool all year around.  This is due to cool ground temperature affecting the temperature of you crawlspace.  Using it’s humidistat to turn the unit on and off, your crawlspace dehumidifier should be able to switch on and run when the humidity level is high, regardless of temperature.

As you have seen from our chart in the previous report, some dehumidifiers only work down to 55 degrees.  These units will do nothing all winter long, during cold rainy days when they should be running.  Others units use a high temperature gas to defrost the coils, allowing a full temperature range down to 33 degrees.  We HAD to incorporate this hot gas reheat feature into our crawl space dehumidifier units because it is ESSENTIAL to guarantee consistent mold and moisture control.

Another big feature that could be overlooked is SIZE.  Heavy duty equipment often comes in big packages.  Crawlspaces built to code can be as shallow as 18 inches… plus you will want a few inches of extra room to get it in position.  It needs to either fit between standard 18 inch floor joists, or rest on top of a cinder block.

Some units are too big for any proposed crawlspace installation, forcing you to buy and install extra ductwork so it can sit above the crawlspace.  Even if you have a large crawlspace, a smaller unit is easier to handle and install.  The hardest part is generally getting it through the vent opening.  A larger unit can end up costing you a lot more money to make it fit in your home.

Dimensions of the dehumidifiers were chosen specifically to fit in any crawlspace built to code.

Beware of what you see online.  Photographs can be deceiving.

Depending on the angle of the picture, crawlspace dehumidifiers may look smaller or larger than what they are.  Crawlspace humidity during cold weather is often overlooked because the warm house above feels dry.  The mold factory below your home keeps growing and polluting your home regardless of the warm temperature and dry humidity of the home above.  As long as it’s cold and moist below, mold, dust mites and bugs will continue to thrive.  Look at the numbers and remember how they relate to your crawlspace conditions.