I'm in the process of installing a forced air outdoor wood burner in my shop. I don't have a lot of options where I put the supply and return so they will only be about 8 feet apart. I'm just running the supply and return through the wall, not going to try and mess with multiple outlets or anything, just a simple system to heat the shop. One thought I had was to put an extra opening up high on the wall in each location so I could send a little heat up higher or maybe pull a little return from above. Just some options to move the heat a little better. So my question is what is the prefered and proper way to run duct up the wall to another outlet/inlet? It's a 2x6 wall cavity, I haven't run across a duct that fills that space. My thought was to just line those two spaces with metal. Is there a better or easier way? The heater has a 10" supply and a 12" return. I plan to just run both in 12" though the wall. I know the wall space isn't equal in area so I could never move all the air through the upper opening, it would just be a portion of the air. Any thought or suggestions?