Product review (5 stars): Awesome control over furnace blower fan speed
A little challenging to install, but the control over system speed is amazing. Much quieter whole-house-fan operation and smooth transition between speeds means home occupants don't even know it's running.

It can be set up to run at a constant low speed even when no fan signal is supplied, which is great for equalizing temperatures throughout the house without having to run the fan at 100%. I suspect I'll see energy savings as well.

This is very challenging to install for a homeowner without prior HVAC experience, but you should be able to do it if you are good at figuring things out.

It's helpful to attack with a basic understanding of furnace blower technology - there are two voltages supplied, full 110v to the motor windings and a 24VAC circuit supplied to the fan control. When a 24V circuit is applied to one of the signal wires, the fan will spin. Several wires are provided, each of which will spin the fan at a different speed. You can wire up your system to spin at a lower speed for fan control, or a higher speed for furnace, humidifier or AC control. It's pretty neat.