It depends on the design temperature of the baseboard system. They often run at 200 degrees or so, and if so, I would not trust PEX at that temperature.: I have baseboard heaters which are old and rusty… ugly… I want to replace the heaters with Runtal baseboards but I was wonder about replacing some of the copper delivery pipes with Wisbro PEX flexible tubing. Have you heard anything on the quality and durability of the flexible tubing available for baseboard heating systems? Original system is 32yrs old…