4" Z-Vent Concentric TWH Kit w/ Mixing Box

I purchased this unit for my Takagi T-D2-IN tankless water heater. There is another horizontal install concentric vent unit listed on the Takagi manuals but that one is bulkier and harder to install into a tight space. Unfortunately, I had to replace the bulkier one with this narrower one with the mixing box. The stock pictures are not really good. The mixing box itself is on the inside end of the double layered concentric vent tube. The box has two outlets, a 4" outlet for exhaust air and a 3" outlet for intake air. The exhaust outlet is directly behind the thru-wall tube so that the exhaust air is not blocked or hindered, in any way, on its escape path. The intake outlet is right next to it on the mixing box, but the mixing box can be rotated to a vertical orientation if so desired. (I did this because the space I had was very tight.)