Compressed Air Piping

My compressor is in my garage. My shop is in my basement. My garage is unheated. I am concerned with running black iron between the two spaces because the the pipe will have condensation/ice form in the basement. How can I prevent this? Also, what is the best way to remove water from the line periodically? I intend to use a drip leg, can I simply add a valve at the bottom of the drip. I don't intend to keep the line under pressure. Only when I need it.

You can insulate the pipe.
I've also used copper pipe for air lines.

There are condensation traps that you can easily plumbing into your air system. They would be use instead of a drip leg. They have a clear bowl that allows you to see how much moisture is present and a button on the bottom that you can drain the water. If you are going to use your air for paint spraying, they make other moisture traps also. I opted to use copper for my system because of no rusting problems, and much easier to install...no cutting and threading. Well, cutting of course, but it's easier to cut copper than iron or steel. I'm very pleased that you do not plan to use PVC!

You can also pitch the pipes toward the condensate traps.

Depending on what you are doing an air drier might be a good investment...

How far to insulate

How far into the room should I insulate the pipe. Is 8-10 feet enough. Thanks for the copper suggestion.

air

A moisture remover at the compressor would be the proper option to avoid the problem in the first place. IF there could be condensation, then you do need drip legs with petcocks on them at each drop, and possibly filters to remove any contaminents. You would have to insulate the entire pipe when it passes through the cooler area. Why not use galvanized and eliminate the possibility.