I have my compressor in the garage, which is separated from my shop by about 4 feet of open space. I want to plumb an air line from the compressor to the shop. Question is, go thru the wall of the garage, then down and underground, and then up and thru the wall of the shop, ***or*** thru the wall of the garage, then up, across the space and thru the wall of the shop. Considering black iron pipe, or maybe galvanized due to the moisture here in Oregon. Don't want to use PVC or CPVC. Has PEX proven OK for compressed air? Moving the compressor to the shop is not an option.