Nope, the combustion fan runs all the time, Not sure if you change the Coaltrol Setting to TRIBURN if it would control it differently?? The CoalTrol guys can probably answer that.
BUT, you will get the most complete burn if it runs at full. If you slow it down and you need more to heat up your house when the thermostat is calling for heat, you may get unburnt stuff and/or not enough heat output if you slow it down.
The blowers are sized properly for good complete burn, if you replace it with a higher flow (CFM), you would get it TOO hot and fuse the coal and make "Clinkers" (been there, done that!), if you get it too low of flow, it may not burn completely or produce good heat. Only reason to SLOW it down if it was the wrong size (CFM) blower.