Powered attic fans can help pull hot air out of the attic in the summer to keep the house cooler. They can also pull hot air out in the winter to prevent a variety of roof problems caused by moisture buildup. Powered attic fans can be roof fans that are mounted on top of the roof, or they can be gable fans mounted on an attic gable. There is also a difference between an attic fan designed to move air only through the attic area and one that is used to cool the entire house. Both may help to lower cooling bills in the summer and protect the roof and structure from moisture problems in the winter.
Attic designs typically contain one or more vents that allow air to flow in and out of the space. Without any type of air ventilation, the heat could build up year-round. In the summer, extreme temperatures in an attic space could make it hard to cool the whole house. Winter comes with a different set of problems that result from hot attics, such as condensation and melting snow and ice on the roof. While vents are necessary, powered attic fans may also be needed to move enough air through the attic space to keep the temperature at an acceptable level.
A powered attic fan designed to cool the whole house will typically be installed on the roof. These fans are designed to pull air from the bottom floor of the home through the windows all the way up to the roof and out. The circulating air can help cool a home in the summer by several degrees. Some people may still find air conditioning necessary in the hottest months, however, because the temperature in the home will only typically ever get as cool as the temperature of the air being pulled in through the windows.
Fans designed to move air only through the attic space are generally either installed on the roof or on a gable in the attic space. Gable installations are often a little easier because this type of fan installation does not require the installer to get on the roof. Powered attic fans come in styles that allow the fan to sense the heat in the attic and kick on when it reaches a certain temperature. They can also be set to stay on, or they can be controlled with a simple on and off switch.
The main need for powered attic fans in the summer is to keep a super-heated attic from heating the whole house. Heat rises, so the attic can act like an oven sitting just above the living space. In the winter, heat rising from the warm house can raise the temperature of the attic as well. The resulting condensation may promote mold and mildew growth, rot wood framing and ruin items kept in attic storage. Even a space with good attic insulation can get hot enough to melt snow and ice that can refreeze on the edges of the roof to create ice dams capable of damaging the roof and walls.
Powered attic fans are designed to prevent these types of problems. Large spaces may need more than one fan to cool the area properly. Solar-powered fans are an energy efficient option that does not require electrical power to run, but may only operate when in full sun; hot and humid days that are overcast may not provide enough sun power to keep the fan cooling the attic unless some sort of backup power system is in place.
