I recently finished most of my basement, including a drywall ceiling. Underneath the drywall are several HVAC lines that branch off the main line. Each of those lines had a shutoff twist-thing, and I *thought* I had made sure they were all open before sealing off the ceiling. Naturally, as soon as winter came, one of the second floor bedrooms turned out not to have heat. It's only getting a trickle of air, so I assume that I probably left the shut-off closed on that line, or that it's blocked somewhere else. The only problem is that I don't know how to find the line. Measuring the house seems theoretically possible, but prone to error. If I hire a duct-cleaning company, can they run a camera through the ducts and tell me where any obstruction is? What should I ask for? Thanks!