Rheostat Controls

Are there controls within some/all rheostats that allow one to vary the power when the rheostat is turned down to its lowest setting? Said another way, does the lowest setting on some rheostats send 50% of full power while others might send only 20% or less, and are there adjustments on rheostats to vary how much of maximum power is sent on the lowest setting? If so I would like to turn my down to a much lower %.

I ask because I purchased the following kit:

http://www.espenergy.com/centrax_variable_speed_c ... ol_kit.htm

It operates in 8" flex duct, and pulls heat from each side of an Alaska Channing III. I didn't know how much CFM to get in a fan, but I also didn't know how much static pressure I'd have in a final configuration. So I bought a fan with too much CFM (listed as 650) and thought I would be able to use the speed control to lower the CFM to at least 300. The problem is on its lowest setting, the CFM seems to only fall a very little, maybe to only 600.

The thermal protection is this fan is set at 140, but its different in that it automatically resets if this temp is exceeded once it falls below 140 degrees. At around 600 cfm the air is no where near 140 degrees, but the point is that since the thermal protection automatically resets there's no risk to hitting the 140 degrees and having the fan shut off for good.

The rheostat on the Channing III seems to lower the speed by at least 50%, so I thought I'd have similiar control powers. Apparently, not all rheostats are the same in this feature.

I have a call into the manufacture of the fan/rheostat, but I won't be able to speak with them until Monday. With all of the knowledge is this forum, I thought I would post this and see what everyone knows!

I found the answer. Here's a link to a pdf that helped me figure it out.
**Broken Link(s) Removed**The minimimum speed control on the model I have kbwc - 13k is as shown on the top left of page 4. On the side view the little circle that is in the center controls the minimum speed.