Carbon dioxide (R744 or CO₂) refrigerant is increasingly being used in supermarket refrigeration applications, is utilised in hot water systems, and has the potential to be applied to smaller sealed unit applications.

CO₂ is non-flammable and non-toxic (at low concentrations), with a global warming potential of 1.

Managing CO₂ in systems does require significant care, however, as the systems operate at much higher pressures, similar to those in scuba tanks. At high concentrations it can also be toxic and cause asphyxiation.