The plumber installed the baseboard radiators in the garage attic, which is the last of the heating equipment. After all pipes are soldered together, the plumber pressure-tests the pipes with 50lb of air, checking for leaks. Given that I installed all this piping in a hurry the day before the drywall went up, I've been sweating this moment for a couple of months. Fortunately, all my plumbign was good and the attic now has heat!