Makes no sense… vague and not true… based on what size fan??? How in the world could a vent be more effective than a fan other than energy efficiency… Wouldn’t the most effective system be the one that changes the most atmosphere the quickest. How would a vent do this if no wind exists… How would it do this better than a fan???
IMO, fans are not required when you have a properly designed vented roof. Properly designed means intake at the eaves and exhaust at the ridge. Properly designed soffit vents allow fresh air in while the hot air rises out the top.
Of course, properly venting a roof that is poorly vented can be difficult or costly, which is why some contractors install fans instead. In my opinion its a waste of power and can lead to conditioned interior air being pulled into the attic space (or hot attic air being pushed into the living space). This is because the fans are typically installed without thinking of intake/exhaust.
Overall I see them as a shortcut. Rarely do I see a situation where the fan was a) required or b) properly installed. I should note that there is very little literature showing that ventilation increases the lifespan of the roof, however, there are lots of other reasons to have a properly ventilated roof (moisture, energy efficiency, redundancy).
Are you a fan salesman I guess you have never witnessed a home that burnt to the ground because of a cheap locked up fan motor with no thermal overload installed. In the attic out of sight and out of mind how often does one enter the attic to see if the fan motor is operating. I don’t put fan motors in my attic and surely don’t recommend to my clients that they do either;-)
Soffit and ridge vent. Hot air rises.
Configuration, location, size, quantity of vents [with and without fan(s)], to name just a few factors that each effect the end result.
Most homes leak the most through the ceiling to the attic. The fan comes on when the OAT is hot. The home’s A/C also comes on at that time. Therefore, the attic fan is drawing conditioned cool air to the attic an to the exterior. I do not recommend them. Also agree with Charley about the fire potential.
Interesting theory but just a few minutes researching and reading and hmmm didn’t find much positive unless someone was selling.
“In many homes, powered attic ventilators pull conditioned air out of the home and into the attic through ceiling cracks. The net result: powered attic ventilators increase rather than decrease cooling costs”.
“A more alarming problem: researchers in Florida and North Carolina have shown that powered attic ventilators can depressurize a house enough to cause water heaters to back draft. Since back drafting sometimes introduces carbon monoxide into a home, the phenomenon can be dangerous”.
“Powered attic ventilators, already suspected of using more energy than they save, can also create excess moisture, structural problems, discomfort, and combustion safety problems for home occupants”.
Figure 1.Effects of powered attic ventilators on eight North Carolina homes. Excessive air flow and house depressurization caused problems in each of the study houses. All of the houses were wasting energy (and money), while some also had moisture and discomfort problems, or even a serious backdrafting hazard.
Some more: https://www.dom.com/about/conservation/pdf/attic_ventilation.pdf