Ground to Attic Fan

Ground to Attic Air Flow

• Ground to attic fans — also known as whole-house fans — create a “whole house” air circulation effect by pulling airflows through open ground floor windows. Situated in the attic, the fan suctions hot indoor air up and out through the fan opening along an attic wall. During the warm months of the year, heat accumulates inside a home as outdoor temperatures rise. By running the fan during cooler times of the day, hot indoor air is replaced by cool incoming airflows. So, it’s best to run the fan when outside temperatures are lower than the temperature inside a home.

Positive Air Pressure

• The airflow generated by a ground-to-attic fan creates a positive air pressure within the attic portion of a home. This positive air pressure helps to push air out through the attic vents, which helps to enhance the suction effect created by the fan. Positive air pressure can also cause attic air to seep through existing spaces and openings between the attic and bottom floors. Pressurized air from the attic can seep through openings surrounding ceiling light fixtures, plumbing vents and exposed beams. These leaks weaken the overall cooling effects of the fan. Sealing and caulking open areas can help reduce air seepage and improve cooling capacities.

Fan Sizing

• Fan capacities are measured according to cubic feet per minute, which indicates the amount of air a fan can move at a time. The square footage area within a home determines the amount of airflow needed from a ground-to-attic fan. Determining the fan size for a particular home space involves multiplying the total gross square footage amount by the height of the ceiling. So, a home with 8 foot ceilings and an area of 1,500 square feet would have a gross volume of 12,000 cubic feet. According to the National Renewable Energy Laboratory's reference site, a properly sized fan would have a capacity of one-half to one times the total cubic footage area of a home. This means a home with 12,000 cubic feet would require a minimum fan capacity of 6,000 cubic feet per minute.

Effects

• Ground-to-attic fans come with one-speed or two-speed settings. Two-speed fans provide strong airflows with quick cooling effects at higher speeds, and ongoing cooling effects on the lower speed. As airflow results from suction forces, a ground-to-attic fan can cause combustion-powered appliances, such as gas furnaces, to backdraft if the appliances sit within a home’s conditioned air space or living space. Backdrafting occurs when suction forces pull air out of an appliance’s combustion chamber. This causes combustion air imbalances within the appliance, which affects efficiency levels and can potentially release dangerous gases inside the home.