Low Cost Cooling Options

By Paul Bianchina

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If your house gets uncomfortably warm or stuffy during the summer and you're looking for a lower-cost, more natural cooling alternative to installing air conditioning, a whole house ventilation fan may be the perfect solution. Whole house fans have an installed cost that's only a fraction of central or wall-mount air conditioning -- around $300 to $400 for a do-it-yourselfer -- as opposed to $1,200 to $1,500 for a wall-mount air conditioner or $2,500 and up for central air conditioning added to an existing duct system. In addition, operating costs can be as little as 10 percent of the cost of operating an air conditioner.

Whole-house ventilation fans operate on a very simple principle. The fan unit is mounted in the ceiling in a central location -- typically in a central hallway in a one-story house, or near the top of the main stairs in a two-story structure. When the fan is activated, it draws a large volume of cooler outside air into the house through open windows and doors, pushing the warmer inside air into the attic and then out of the house through ventilation spaces in the roof or gable end walls.

The result of this air movement is to cool your house in three ways: by replacing hot air inside the house with cooler air from outside; by continually flushing hot air out of the attic, which reduces attic temperatures and the resulting heat radiation it causes; and by creating a gentle breeze in the house that cools the occupants by an evaporation effect across the skin. Another advantage over air conditioning is that you are flushing stale air out of the house and replacing it with fresh air, while air conditioners recycle indoor air and, in today's tight houses, can contribute to unhealthy concentrations of indoor air pollutants.

Fan Types

There are two basic types of whole-house ventilation fans, direct-drive and belt-drive. Direct-drive fans have a motor that is attached directly to the fan blades. These are less expensive than belt-drive models, and work fine for small to medium size homes. The primary disadvantages are a higher noise level in the motor, and more vibration in the fan.

Larger fans typically utilize a belt-drive motor, in which the motor is attached above and to the side of the fan and utilizes a belt and pulley system to turn the fan blades. Belt-drive models are quieter, the motors use a little less electricity than direct-drive units, and the belt and pulley arrangement allows for larger diameter fans with more steeply-pitched blades, which results in a higher volume of air movement. The initial cost of the belt-drive models is a little higher, but that is offset somewhat by lower operating costs.

Both types of fans are designed to be mounted into a hole that is cut into the ceiling. Some smaller types of whole-house ventilation fans -- those with 20-to 24-inch diameter fans -- mount on top of the ceiling joists or even in between them, allowing easy installation with no cutting of the joists. Larger units utilize 30- to 36-inch diameter fans, and require that the ceiling joists be cut and supported to form a square hole. Complete instructions are provided with the unit, or you may need to consult with a qualified contractor to do the framing.

Both types of fans also utilize a louvered cover, which mounts to the ceiling to cover the fan. When the fan is activated, the air movement pulls the spring-mounted louvers open, allowing the air to flow into the attic. When the fan is off, the louvers automatically snap back into the closed position, concealing the fan and preventing cold attic air from leaking down during the winter. All of the fans operate on 120 volts with a power draw ranging from around 3.5 to 9 amps, depending on the CFM capacity, and are controlled by either a manual, wall-mounted on/off switch or a 12-hour timer. Consult with the manufacturer's instructions or a licensed electrician for complete wiring details.

Sizing the Fan

Whole-house fans are rated in cubic feet per minute of airflow (CFM), and, to provide efficient cooling, need to be sized to the square footage of your home. The rule of thumb used by most manufacturers is to take the total number of square feet of living space in your home and multiply it by three to determine the size of the fan in CFM. For example, a 1,500 square foot house would require a fan of approximately 4,500 CFM (1,500 x 3).

As the stale air is exhausted into the attic it requires some means of being able to exit the attic to the outside, so attic ventilation is a very important part of your calculations. Here, the rule of thumb is to divide the capacity of the fan in CFM by 750 to arrive at the total square footage of attic ventilation area needed. For the 4,500 CFM fan in the example above, you would need approximately six square feet of attic ventilation area (4,500 / 750). This can be any combination of soffit, roof, ridge, and/or gable end vents.

Whole house ventilation fans, ceiling lovers, and controls are available through most home centers, larger lumberyards, and plumbing and electrical retailers, typically by special order. Your dealer can also help you with sizing and locating the units for best performance.

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