uneven steam heat

The "good" main wraps around the basement, about 50 feet with two turns. It starts as 3" and end up as 2"? It is wrapped with insulation and has the original main vent(don't know the make) at the end before it drops for the condensate run back to the boiler. The "troubled" main runs through the crawlspace, which is colder than the basement, probably about 50 feet as well. The main vent we just put in is a Dole QV#5, which is piped into a 3/4" swing joint at the end of the main just before it drops for the condensate return. We also have put adjustable vents on the radiators, setting the "good" side to slow and the "troubled" side to fast.

Yes both mains are insulated w/ typical asbestos wrap. Troubled side has three radiators off 2 branches. When we first met this system, the second radiator of branch didn't work. In the crawl where foundation work had been done before, the wrap had been removed and also the pipe was left sagging w/ wrong pitch, and probably full of water. We supported the pipe back in its original position. It is mostly wrapped w/ Armaflex insulation.