Straight Copper Tubes are most frequently employed in HVAC systems as a refrigerant line and in heating systems. PEX tubing is gradually taking the place of copper tubing in applications involving hot and cold water. Copper tubing comes in two main varieties: stiff copper and soft copper. These are employed in cryogenic systems, HVAC, refrigeration, medical gas distribution, plumbing, and compressed air systems. Speciality alloy tubes are an alternative to standard copper tubes.