The ac will be about 10 inches from the wall with a 6inch pipe, then go to a reducer to make it a 4 inch pipe for another 12 inches thru the wall and out of the house. Cutting the area in half may speed the air up in the choke point but fans work by moving air--once the resistance increases the blades start “slipping”. I don’t remember the tech term but it’s like cavitation on a boat prop; you can put all kinds of power in but the boat goes slower until the blades bite and push the water air does similar. You can put a tachometer on the fan and watch it speed up but it is moving less air. This why duct sizing/flow is critical to set up a system. You don't have permission to access "http://www.homedepot.ca/product/imperial-6-4-inch-reducer-no-crimp/1000102728" on this server. Gurji, that’s what what I got also. I did calculate it after making the statement. In basic duct sizing 4 to 6 is double and 6 to 8 is double, but pi r squared is right. But I only do HVAC part time. If you can shorten the hose significantly from its max length, this will compensate. Very likely a short section of 4 inch diameter through the wall could give full performance. A slightly longer, more gradual transition piece might work better than a shorter more abrupt transition.

You don't have permission to access "http://www.homedepot.com/p/Master-Flow-6-in-to-4-in-Round-Reducer-R6X4/100111736" on this server.