Running airline outside?

If you bury the line outside make sure that you do not bury any gravel or rock against the copper itself. Rocks tend to rub holes in the copper. {When the propane company that my BIL owns would bury copper lines, he would use sand or fine dirt to cover the line for a few inches before filling the trench}.

Good luck (and remember to install good shutoff valves on both ends of the line).

Another thought... if the air supply is to be remote as you say... you may desire to install a remote switch for turning on or off the compressor to save a few footsteps between the garage and basement (maybe a 3-way switch)... just a thought!

Sounds like you got it planned out pretty well. I think 3/4 cu is a very good choice. I assume you are under 200 psig here :o). Either type L or M will work fine for you. For either L or M (with solder joints), the allowable working pressure is determined by the solder used in the joints. That is significantly less that the pressure capability of the tubing itself. See this link. The type L has a little thicker wall and is more expensive. You should consider that if there is any possibility of physical damage to your line. It would be a little better when subject to any abuse. In any event, think about using the 95/5 tin/antimony solder instead of the 50/50 tin lead variety. It will get you a higher working pressure, as the link shows.

Insulating the line will help a lot as long as do not allow any low point "pockets" outside where moisture could collect. You seem to have that all well figured out with the sloping of the line.

Good luck in your installation.

Rod

I suppose you COULD go to that trouble. You should evaluate the possibility of significant physical abuse though. If that possibility is real, rather than minor incidental, I would suggest the use of sch 40 steel pipe rather than copper. That is the "standard" in commercial/industrial settings for that service and would be superior to copper inside a plastic protective shield.

Rod