My sons bedroom has always been cooler then the other bedrooms. We've done the obvious, replaced the windows (very old and leaking air), added/corrected insulation (some missing, incorrectly installed, etc.), added insulation in the attic overhead. All with SOME effect but still not great. I suggested that maybe there was a bypass valve somewhere, though I've never seen anything like it in the house. When we removed the baseboard covers to look we discovered another "economy" job of the builder. He must have run out of the "finned" pipe so finished the job with plain 3/4" copper pipe.

Is there any way to retro fit fins, or something that will do the same job, onto the 3/4" copper pipe? I would rather not have to cut out, about 20', of plain pipe and solder in the new.