Fluid based systems using cross-linked polyethylene (PEX) a product developed in the 1930s and its various derivatives such as PE-rt have demonstrated reliable long term performance in harsh cold-climate applications such as bridge decks, aircraft hangar aprons, and landing pads. PEX has become a popular and reliable option in-home use for new concrete slab construction, and new underfloor joist construction as well as (joist) retrofit. Since the materials are produced from polyethylene and its bonds are cross-linked, it is highly resistant to corrosion or the temperature and pressure stresses associated with typical fluid-based HVAC systems. For PEX reliability, installation procedures must be precise (especially at joints) and manufacturers specifications for a maximum temperature of water or fluid, etc. must be carefully followed.