Regular Dehumidifier: OK in a Crawl Space?

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Regular dehumidifiers are not designed to be used in a crawl space. These dehumidifiers do not have enough capacity to dehumidify crawl spaces, and they are not rugged enough to withstand the environment. A crawl space dehumidifier must be used. These robust units dehumidify large volumes of air very rapidly.

The crawl space of a house is often an area that requires a lot of maintenance. This area is vulnerable to damage caused by humidity and moisture, which leads many homeowners to install dehumidifiers in the crawl space. However, in order to adequately protect the crawl space, the dehumidifier requires a certain level of power and hardiness.

Controlling the moisture and humidity in a crawl space can be challenging, but it is necessary for every home with an underfloor area. Let’s examine the use of dehumidifiers for this purpose, as well as a few other solutions to this problem.

Crawl Spaces Have to Be Protected Against Humidity

International Residential Code (IRC) R408.1 states that all under-floor spaces between a building and the ground must be moisture controlled. This is to prevent any damage caused over time by moisture and humidity and protect the integrity of the building.

Furthermore, many people run wiring and junction boxes in their crawl spaces. This makes moisture control of paramount importance.

A reliable and commonly used method for controlling the moisture and humidity in a crawl space is to install a crawl space dehumidifier that is specifically designed for this purpose.

Regular Dehumidifiers Are Insufficient for Crawl Spaces

Regular dehumidifiers are not suitable for use in the crawl space under a house simply because their capabilities are insufficient. The dehumidifying capacity of regular dehumidifiers is significantly less than crawl space humidifiers.

Crawl space humidifiers have a much higher capacity for moisture removal. Some models are capable of removing as much as 17 gallons (65 L) of moisture per day from an area spanning over 7000 ft2 (650 m2).

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By contrast, regular home dehumidifiers are only capable of removing around 2.6 gallons (10 L) of moisture per day from a normal-sized bedroom.

These figures vividly show us that regular dehumidifiers are not suitable for use in crawl spaces, as they will not remove enough moisture from the area to prevent the damage that high levels of humidity can cause.

Crawl Spaces Are Too Harsh for Normal Dehumidifiers

Regular home dehumidifiers are designed to be indoors and usually in rooms such as bedrooms that are particularly shielded from more extreme environmental factors like excessive heat or cold. As such, these devices are not particularly rugged, nor are they designed for use in harsh environments.

The design features specifications of regular dehumidifiers mean that they will be damaged beyond repair if they are used in the tough environment of the crawl space for any length of time.

However, commercial or crawl space dehumidifiers are built for continual use in the very harsh environment of the crawl space.

These machines are designed with rugged exteriors, waterproof technology, hard-wearing mechanical and electrical components, and they are built from much stronger materials than the standard plastics of regular dehumidifiers.

Crawl space dehumidifiers are designed to withstand harsh environments for long periods, while a regular dehumidifier in the same conditions will only last for a fraction of its intended lifespan in the same conditions. 

Regular Dehumidifiers Not Designed for Constant Use

Any dehumidifier that is used in the crawl space of a house must run continuously to be at all effective. The levels of humidity in a crawl space rise so rapidly that the dehumidifier used in this area must be left running at all times to reduce the humidity in the space.

Regular dehumidifiers are not designed for constant use. Even indoors, regular dehumidifiers can not handle long periods of constant use. Most of these devices are equipped with an automatic shut-off function to prevent the potential damage caused by prolonged use. 

The components of regular dehumidifiers will wear out very quickly if used continuously.

In comparison, crawl space dehumidifiers are designed to run continuously, even in the harsh crawl space. The components of these machines, such as the pump, the motor, and the electrical components are built to be durable and hardy enough to withstand constant use without sustaining damage or wearing out too quickly.

Requirements for a Crawl Space Dehumidifier

Crawl space dehumidifiers are unlike other types of dehumidifiers. As I noted above these machines must be able to withstand long periods of use within the crawl space under a house, which requires them to be exceedingly tough when compared to other dehumidifiers.

These units must have rugged external housing that is durable enough to withstand the harsh environment of the crawl space without tarnishing, rusting, or breaking down in any way.

Commercial dehumidifiers must be capable of removing very large quantities of moisture from the crawl space, at least ±9 gallons (35 L) of water per day.

These machines should also be compact enough to fit comfortably within the crawl space and to be placed in any area of the crawl space to be as effective as possible. These units should also be equipped with either a very large collection tank or the ability to pump water out from the crawl space.

A high-capacity pump and motor and heavy-duty filters are also requirements for dehumidifiers of this type.

Some extra features that many modern crawl space dehumidifiers are equipped with include:

  • Defrosting systems.
  • Adjustable wheels.
  • Remote control.
  • Digital touch screen control panel.
  • Auto-restart capabilities.
  • Temperature readout.
  • Lightweight design.

Some of the best modern crawl space dehumidifiers with these features include:

Do Encapsulated Crawl Spaces Need a Dehumidifier?

Many homeowners choose to encapsulate the crawl space of their house. This is a good way to help mitigate the humidity in a crawl space. 

In fact. Installing a dehumidifier is pointless unless the crawl space is encapsulated.

However, an encapsulated crawl space is still susceptible to high levels of humidity, as moisture is likely to escape from the ground and collect within the encapsulated crawl space. Other issues arise in encapsulated crawl spaces, such as the accumulation of harmful gases that will seep into the living space from the crawl space.

Image of a crawl space with dehumidifer and sump pump

A dehumidifier should always be used when a crawl space is encapsulated.

According to the International Residential Code R408.3.2.4, all unvented crawl spaces are required to be fitted with dehumidification of at least 8.7 gallons (33 L) of moisture removal per 1000 ft2 (93 m2) per day.

This international regulation means that if your encapsulated crawl space is not well vented according to IRC regulations, it is required to have a high level of dehumidification to prevent damage to the building and harm to the residents thereof.

Using a high-performance crawl space dehumidifier is the best way to comply with these crawl space regulations.

If you are looking to waterproof your crawl space, check out my article on the Difference Between Drylok and Drylok Extreme.

Do Whole-Home Dehumidifiers Work in the Crawl Space?

Many houses have whole-home dehumidifiers built into the HVAC system. These systems are very effective for dehumidifying the living areas within the house, but can this system be used to dehumidify the crawl space as well?

Whole-home dehumidifiers will work in the crawl space if they are set up correctly, i.e., the system is run into the crawl space and dry air is pushed into the crawl space as well as the rest of the home by the HVAC system.

A system like this can be complicated, but it will function well to dry the crawl space. That being said, most experts advise that the crawl space should be dehumidified with the use of a crawl space dehumidifier. 

Experts state that dehumidifying the crawl space before dehumidifying the rest of the house may actually eliminate the need for a whole-home dehumidifier, as most of the humidity in a home comes from a humid crawl space.

Alternative Ways to Prevent Crawl Space Humidity

Dehumidifying units are not the only method of preventing crawl space humidity. 

There are several other methods that are effective for this purpose, but the best options are those laid out in IRC section R408 regarding the ventilation and dehumidification of crawl spaces:

  • Class 1 vapor retarder material can be used to cover the surface of the ground in the crawl space if the area is ventilated according to IRC regulations.
  • Continuous mechanical exhaust ventilation can be installed. This system must exhaust 1 ft3 per minute for every 50 ft2 (4.7 m2) of the crawl space.
  • Conditioned air can be supplied t the crawl space at a rate of 1 ft3 per minute for every 50 ft2 (4.7 m2) of the crawl space.

These regulations state that good alternatives for a crawl space dehumidifier are to make sure that the crawl space is exceptionally well ventilated, the HVAC system supplies dry air into the crawl space, or to install a continuous exhaust system to pump air out of the crawl space.

Another good alternative is to install vapor retarder material that covers the ground in the crawl space. Some class 1 vapor retarder materials include:

  • Polyethylene film
  • Glass
  • Sheet metal
  • Foil-faced insulated sheets
  • Nonperfurated aluminum foil

Start With a Dry Crawl Space

A good way to ensure that any dehumidification measures that you implement in the crawl space of your house are effective is to start with a crawl space that is as dry as possible.

This includes repairing any water leaks, pumping out any large puddles, blocking any entrances for groundwater flow, and even removing any excessively wet soil before implementing any dehumidification, such as the installation of a crawl space dehumidifier.

Controlling the moisture in a crawl space is also one of the main reasons not to vent your bathroom fan into a crawl space (doing so contravenes building codes).

These preliminary measures will ensure that your crawl space will dry out quickly, and it will help to prevent any future moisture issues in the crawl space.


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