Based on our experience in the industry, the answer is yes. Attic fans do work. They will help to circulate air in the attic and ventilate the space, bringing it closer to the outdoor temperature. Attics can reach extremely high temperatures during the hot summer months and collect excessive moisture during the winter months. Attic fans will help with these problems.
Do they really save a lot of energy? The answer to this ultimately depends on where you live, the type of fan you install, and whether your attic air is sealed correctly.
For those who live in cold or temperate climates that never reach 80 degrees, attic fans may not be worth the price of installation (if you are only concerned about energy savings). Passive roof vents may be sufficient, and if your goal is to save energy, you may want to consider air sealing or adding insulation.
There is also the debate about electric versus solar fans. Electric fans will do what they are supposed to do, but you need to consider the average cost of powering them. Many electric attic fans also only come with a 1-3 year materials warranty, so you may need to replace them at some point. Solar fans will work all year round at no cost to you and have a much longer warranty.
So do attic fans really work? Yes! But ultimately it depends on what your goals are. If you are looking for significant energy savings, combine the fan with other practices such as adding insulation and air sealing the attic. If you are simply looking for increased ventilation to improve comfort and protect your roof, then installing an attic fan will certainly help.