A:Answer The Vent Air Flow (CFM) for the LG 2.0 cu.ft. Over-the-Range Microwave Oven, Model # LMV2031ST is 400. This unit can be vented in one of three ways, roof-venting, wall-venting or room-venting. Ducting will be needed for wall-venting or roof venting, but it is not needed for room venting. The microwave is shipped with the blower assembled for roof-venting. If you are in need of any assistance, have additional questions, or would just like to see our helpful tips, check us out on Twitter @LGUSSupport Facebook https://www.facebook.com/LGUSA/ or you can give us a call at 800-243-0000. ^CP