electric motor question

I was going to buy an inline fan that uses a brush type motor so it can be speed adjusted with a controller. My question is should I buy the next size larger than what I need and conrol the speed or just buy the size I need. Does slowing a larger motor down still use the same wattage as the motor at max with the controller using the excess?

Here are the fans I was looking at.
http://www.atmosphere.com/English/allfans.htm

If I remember correctly from school, the excess is dissipated as heat at the controller.

Just buy the size you want/need. I thinnnnk I'm right, perhaps some one that truly understands will pipe up and inform us, but, I have it in my mind that in the old days a speed controller used electricity. As you say, it used the excess. Now, with solid state digital controllers, they just dribble out the power needed & don't use the excess so to speak. If the fan was set to half speed, it would use about half the electricity. With either the old style resister type, or the new solid state type, at full speed, the controller uses zero power, it just lets full voltage through.

The VTX600 with 449cfm will work for me now but I may want to add another room to the system later on and at that point I feel the VTX800 with 747cfm would be a better choice and there is only a $45 price difference between them $173 to $218. but twice the current draw .8amps to 1.6amps

OK, You got my curiosity up enough.... I have a router with an aftermarket variable speed device. I just went & put an amp meter on it. At full speed it draws 4.2 amps, when I lowered the speed, the amps lowered with it. At slow speed it drew 2 amps. SO, that means for sure, a *new* speed reducer doesn't just suck up the extra juice. I'd say if you wanted to get the larger one and slow it down with a rheostat, go for it. That is, granting the fan is not hurt by reducing it's speed.

Thanks for the info Freddy.