"We have no vents in place leading from the attic to the second floor"

The whole house fan would go in the attic and draw air from the second floor. Our fan draws air from the hallway centrally located on the second floor but there are options for fans in each room. The installer would determine whether you need more attic venting to the outside of the house.

We have a 2700 cfm whole house fan and LOVE it. When it cools down in the evening we open the windows on our 2nd floor and turn the fan on. It's amazing how fast is cools the home. Since the whole house fan vents to the attic it also turns the air over in the attic helping to cool the attic. We have been very happy with our whole house fan.

There are some things to consider though. I've read comments from experts on here about fire hazards due to the suction from the fan. I believe this is primarily a concern for those with water heaters in the home. Our water heater is in our garage and so the flame is not subject to the pressure variation caused by the fan. Hopefully some experts will chime in on the things to look out for.

Attic fans are not nearly as good for attic ventilation as are vented soffits and a ridge vent. They don't move enough air to really keep an attic cool. Whole house fans only work in climates where the exterior temperature and humidity is pleasant enough for you to want to introduce that air into your home. They don't work in conjunction with AC. You don't want to introduce unconditioned air into an environment that you are trying to condition. If your second floor is hot, a second zone and better return ducts is probably a good idea to consider. And the life of your roof will be greatly improved with proper attic ventilation from soffits and ridge vents.

Correct ridge and soffit vents do as good a job without using any energy.

If the vents are not correct using a fan to vent the attic will not work well either, and may depressurize the attic enough to pull conditioned air from the house.