Your best choice is our TA3800 because it comes with an infinitely variable speed dial and has a 15 year warranty. This fan gives you excellent air flow at just 505 watts full speed. It is a easy to install with no helper because it has a built in damper and it hangs on a pre installed metal square tube attached to the rafters.

The TA3800 is very quiet when hanging from your rafters. And you can see the hanging bracket below that makes installation a breeze. The large picture shows how well the motor mounting brackets center the motor and hold it in perfect position above the internal air damper flaps. The brackets have steps that position the motor straight and level. The motor is held by 2 strong stainless steel straps. The propeller has 8 blades each with a 50 degree bite for maximum air flow. It is balanced perfectly to eliminate all vibration at all speeds.

Above left is the modern EC motor (Electronically Commutated) that has infinitely variable speeds. In the center is  is the fan  with the hanger that makes installation easier and to the right is a view looking at the bottom of the motor and fan and damper assembly. In use this is horizontal and the damper flaps close due to gravity. You can see damper flap in the center. Look closely and you can see the hinge point to the left that is bright silver and the right flap is hanging down. In use, the damper flaps close until the motor is on, then open. When closed, the attic air cannot fall down into your home.

Above is the frame and grille for under the ceiling and the duct on a ring for over the clg.

Here are the technical specifications
Air flow variable from 50 CFM to full speed using a dial like a light dimmer.
Input AC 120 VAC 1 Phase
Input AC power varies from 50 watts to 505 watts maximum at full speed.

The speed control dial shows your speed selection and the 12 hr timer shows the time.

Here is a nice install in Salt Lake City – This was done by Casey in 2015.

Above is the fan held by the rafters and below is the intake grille and frame.