[I posed this question earlier today on another web sites forum, but didn't get any answers, so I'm hoping someone here has some advice. Thanks]
I am in the process of insulating my hot water (not steam) heating pipes in my unfinished basement. These are black pipes feeding radiators on the upper floors. I am using 1"-thick wall fiberglass tubes, with ASJ facing. I'm about to insulate a section of 1" IPS pipe, specifically supply pipe. My system is set at a high limit of 150 degrees. The return pipe is running in parallel just about exactly 1" away from the supply pipe, so in this case I will probably not be insulating the return pipe there since there isn't sufficient clearance. The issue is that the pipe insulation on the supply pipe will just butt up against the return pipe. Specifically, the ASJ will butt up against it. I've read that the ASJ itself is rated up to 150 degrees F. Since my system is set to a high limit of 150 degrees, the return pipe should be less than 150 degrees (and when I've measured it, it is, but of course it's not very far from 150). I've also read that the auto-ignition temp of paper (in general) is around 450 degrees (not sure if that's F or C). Either way, I'm trying to make sure that having the ASJ butting up against the return pipe is safe. I'm wondering what happens to the ASJ if it gets 10 or 20 degrees above 150 degrees. Alternatively, I could do a relief cut in that area so that the ASJ does not touch the pipe, or I could cut away a long section of ASJ entirely, but I'd rather not do that unless I have to. Thanks for any advice.