Hempsouth, that's interesting to hear. My PVC setup would only involve 1 elbow about 2 feet from the exit. It is a very short run to the external vent. I can not seem to find the 4" to 2" reducer except to use a jerry rigged 4" to 2" bushing. I have significant preference for the 4" to 2" reducer scenario as it involves significantly less work / changes to the current exhaust configuration. Clearly I need to do a bit more homework on this.