When finishing a basement to use as a livable space, basement ventilation becomes important to keep air flowing in and out of the basement, but more importantly to keep moist air from stagnating and creating mold. Mold and mildew can pose a health risk if you spend a significant amount of time in a room, and while installing a fan can certainly help, it may not be enough to adequately increase basement ventilation. Dehumidifiers can help reduce moisture in the air, carpets and walls, and they can help eliminate or reduce musty basement odors common in damp spaces.
Perhaps the best option for basement ventilation is an air exchange system. These systems take air from the outside of the home and suck it inside, while venting damp air inside the home and allowing it to escape outside. This transfer allows dry air to circulate through the basement, drying out the walls, carpets, floors, and other materials. This system accentuates the importance of basement ventilation, as the user will be less at risk for termite infestations as well as mold and mildew, which can cause respiratory problems in humans and pets. Dry air also means less chance of structural rot in beams, joists, and studs.
If an air exchange system is not an option for you, a simple fan and dehumidifier combination may suit your basement ventilation needs. A fan can blow damp air out of the house if properly ventilated. A portable box fan may be placed in a bulkhead or doorway to the outside, but keep in mind that the doors will need to be open so the moist air can escape. A dehumidifier is perhaps a more effective method. This device sucks up moisture in the air and traps it in a tank inside its shell. It is important to choose a dehumidifier that is the appropriate size for the basement in which it will be placed. A dehumidifier that is too small will not pull enough of the moisture out of the air to be effective. A dehumidifier's tank must be emptied regularly to avoid overflow.
The least expensive option in terms of up-front costs is a combination of fans and dehumidifiers, but this option may not save you money in the long run. As a basement ventilation system, the fan and dehumidifier option will raise heating costs and electricity bills, since fans need to be placed either in open windows or open doorways, and dehumidifiers need to be running fairly constantly to be effective. The up-front cost of the equipment, however, is lower than an air exchange system.