I've just finished installing the radiant heating pipe in the upstairs bathroom. The pipe I'm using is 1/2' PEX pipe with an oxygen barrier. (More on that in a later post.)
I'm working with a 500' roll of pipe, so I've made up a quick n' dirty unspooler out of a couple of long clamps and a piece of 4" ABS pipe. When installing the Pex pipe, it needs to actually be unrolled, as opposed to just laying the roll of pipe on the floor and uncoiling it. If you just uncoil it from the roll, it will get twisted and be almost impossible to work with. (Think of how a garden hose gets all twisted up when you just uncoil it.) By hanging it up and unrolling it, you don't get any twists in the pipe and it installs easily.
I began by putting the end of the pipe down through the floor and into the chase that goes down to the basement. Then I layed the pipe in the long, winding slot in the floor. When I got back to the beginning again, I cut the pipe with enough length to go back down to the basement again. The entire length of pipe was 130'. Eventually, the two ends of the pipe will get connected to the radiant heating manifolds in the basement.