Just installed new water heating system at home. Plumber who install radiators told me that i must insulate pex pipes in crawling space for heat loss reasons. This crawling space not cold in a winter time (about 50 F), but he told me i Must do it right with the fiberglass insulation (cost $6 for 6') , not with polyethylene foam pipe insulation ( cost $1 for 6' at HD). Guy who install boiler (25 years in heating business) told me polyethylene foam pipe insulation is OK and he use it all the time. I need to insulate 300' of the pex pipes and the price difference is hi! For whom I have to Trust?