I have PEX pipe hung under the floor joists in my crawl space. I am inclined to cut fiberglass wall insulation R-14 into strips and run it under the pipe.That will encase it as the floors are well insulated. (R-19 above the PEX & R-14 below) Would that be as effective - less effective - more effective than putting foam insulation around the exposed sections of PEX ?( I really don't want to pull the hangers that attach the pipe to the joists) The cost of insulating this was would be negligible but I don't want to create any moisture problems? The crawl space has a good vapor barrier on the ground. the insulation in the joists has no paper backing.
Should work fine-ish. Use more UN-Faced insulation to avoid moisture problems.
It's only fine-ish (rather than fine) because the pipe is more than halfway through the total insulation, leaving it somewhat subject to freezing if it gets cold in the crawlspace.