Dehumidifiers provide a very important step in conditioning a crawlspace, however, the dehumidifier alone is not going to cut the mustard. There are just too many elements working against it. We sell and install the SaniDry Sedona, which happens to be the worlds most efficient dehumidifier and we would never recommend installing it in a crawlspace without completing the other necessary steps. In order to properly condition a crawlspace we need to eliminate any groundwater seepage, seal off the earths moisture, stop outside air infiltration and last, but not least, condition the space (dehumidify). This last step is where the dehumidifier comes in to play. However, it's not until we have addressed the other 3 concerns that we can effectively "dehumidify" the space. The dehumidifier will just have to work way too hard in a losing battle. This is why it's very common for us to see 3 or 4 burned out dehumidifiers in a crawlspace when we go out to do an inspection!