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Choosing a Drain Method for a Crawlspace Dehumidifier

Tips from a Crawlspace Industry Expert

When you install a dehumidifier inside a crawlspace, one of the decisions to be made is how to divert the condensate out of the crawlspace. You don’t want the water to stay inside the crawlspace, of course. There are two acceptable methods to accomplish this. One is known as a gravity drain system and the other is a condensate pump system. I say two acceptable methods because the third method is controversial and some jurisdictional building codes will not allow you to drain the condensate into a public sewer system. I would not recommend draining it into a septic system, either.

No matter which acceptable method you use, once the water is diverted out of the crawlspace it must terminate away from the foundation wall, similar to how HVAC professionals divert the condensate from a heat pump or air conditioner away from the foundation of the home. I recommend a minimum of 2 feet or more away from the foundation and on a downward slope away from the foundation.

Gravity Drains

A gravity drain is used to channel condensation away from the dehumidifier. In order for the drain to operate properly there must be enough drop from the dehumidifier, through the foundation wall and away from the foundation. You only need about ¼ of an inch of drop per 10 feet of run for the water to drain properly. You must be careful and avoid any slumps in the line. A low area in a drain run will cause the water to back up and flood the crawlspace, thus defeating the purpose of having a dehumidifier in the first place. The backflow could also damage the dehumidifier.

To determine if a gravity drain is possible, you should first determine if you have the drop. I recommend using a water level or a line-level (like masons use) to verify the drop. The drain pipe must be secured and supported, especially if the drain pipe has a long run. The hole through the foundation must be specific to the size of the drain pipe being used. I suggest at least a ¾ inch diameter. Drain pipe material today is inexpensive with options like PVC, CPVC, or PEX. Copper is another choice but one that can be more expensive. Always remember the termination of a drain line from the foundation is recommended to be more than 24 inches on a slope away from the foundation.

Condensate Pumps

A condensate pump has a reservoir that collects the condensate from the dehumidifier and works like a sump pump. Once the reservoir fills to a set level, a float triggers the pump that forces the water down through the drain pipe and out of the crawlspace to the termination spot.

One of the things to consider before making the decision to use a condensate pump is whether you have enough height inside the crawlspace from the ground to the bottom of the framing to install the dehumidifier high enough to allow the proper drainage into the pump reservoir. If you install the condensate pump without the proper drop the condensate will back up into the dehumidifier and spill out onto the moisture barrier. Again, defeating the purpose of the dehumidifier.

Another factor of the condensate pump is it needs power to operate. Having an electrical outlet installed close enough to the unit so the pump can be powered is critical. The power source needs to have a duplex GFCI receptacle installed on a 20-amp circuit so that both the dehumidifier and the condensate pump can be powered from the same circuit. I recommend that a licensed electrician do the electrical installation.

Just like the gravity drain, a condensate pump needs a drain line running out of the crawlspace. Usually this is a ¾ inch piece of plastic pipe. Some condensate kits come with a length of clear plastic drain-line for short runs. For longer drain-line runs, you may have to couple two or more pieces of drain line together.

For All Further Questions

There are several things to consider when installing a dehumidifier inside a crawlspace. The type of drain system is just one of the major decisions that should be made prior to installation of a crawlspace dehumidifier. For more information on condensate pumps and training on the different types of drains, contact the professionals at Your Crawlspace Inc.

Don Richards ACE, CPI

Don Richards Services, LLC

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