I have to admit that my experience with whole-house fans has not always been positive. I remember almost 20 years ago as an HVAC contractor when homeowners would ask me to quote a whole house fan installation, I’d quickly steer them away. The noise from these traditional whole house fans reminded me of my time in the Army being around helicopters. Sure they moved a ton of air but try having a conversation, listening to the television and don’t even think about trying to sleep while it’s running.
Fortunately times have changed and the newer ducted style whole house fans are ultra quiet and extremely energy efficient. This begs the question: “What is a whole house fan?” in its modern context.
Simple Concept
So what is a whole house fan? A whole-house fan is a fairly simple device. The fan is typically mounted above the ceiling of a central hallway (in the top floor of a two-story house) and draws cool outside air in through open windows while forcing the hot indoor air out the existing attic or roof vents. This cycle creates a comfortable living environment and reduces the air conditioning load.
A whole-house fan is effective whenever the outside temperature is lower than the indoor temperature, which is usually in the evenings, at night or early in the morning. It uses just a fraction of the energy of air conditioning, which means drastically lower energy bills for the typical residence.
In dry climates, a whole-house fan is a no-brainer, as it can minimize or nearly eliminate the need for air conditioning completely. What many people don’t realize, however, is that even in most other areas of the United States, you can use it in conjunction with your a/c to dramatically reduce your energy consumption.
Several years ago a study was done on whole-house fans in Florida, and the conclusion was that, while they can increase humidity, they also reduce the temperature in a home. The study involved 384 single-family homes, apartments, and condos, and it showed that by using natural ventilation instead of air conditioning, 777 kWh was saved. So, understanding “what is a whole house fan” reveals that it does reduce air conditioning costs wherever you are.
Obviously, the warmer and more humid the evening air, the less effective natural cooling becomes; however, whole-house fans are often used successfully to complement air conditioning systems. A typical rule of thump is that as long as the outside temperature is 10 degrees cooler than inside, a whole-house fan can begin to reduce the temperature inside the home.
New Design, Easier Installation
The traditional or older style whole-house fan is very large and extremely noisy but can move between 5,000 and 7,000 cfm (cubic feet of air per minute). This type of fan is installed in the ceiling, and louvers open when the fan is turned on. Newer whole-house fans have a typical flow range between 1,000 and 4000 cfm.
The real distinction between the two is that if people want to feel a breeze moving through the house, then they need to get the older style whole house fan. If they are willing to cool the home down slower over a longer period of time, then the ducted style whole house fans work great. They’re quieter and more energy efficient, but they won’t create the kind of breeze that a 7,000-cfm fan will.
Besides being significantly quieter, the new fans have optional motorized, insulated, sealed damper doors; no framing is required during installation; and a smaller fan running all night long will use much less energy compared to air conditioning. In addition, the house will be cooler in the morning.
The one major requirement for a whole-house fan is that the home must have an attic with a certain amount of clearance. In addition, a home must have a sufficient amount of attic ventilation in order to exhaust the air. If there is not enough ventilation, the resulting positive pressure will force hot, dusty attic air back into the house through light fixtures and other cracks. According to Pacific Gas and Electric Company, 1 square foot of unobstructed venting should be allowed for every 750 cfm.
Is A Whole House Fan The Same As An Attic Fan?
There’s a big difference between a whole-house fan and an attic fan. Attic fans are designed to ventilate the attic space only, while whole-house fans are designed to ventilate both the living space within a home and the attic.
The Home Ventilating Institute (www.hvi.org) refers to whole-house fans as whole-house comfort ventilators, and they are designed to bring in cooler outside air, draw it through the house, and push the house air out through the attic vents. Attic fans are used to reduce heat buildup in an attic only.
To learn more about the benefits of whole house fans visit www.CentricAir.com