Definition
R290 is refrigerant-grade propane, a natural hydrocarbon refrigerant with a GWP of about 3 and no ozone depletion potential. Its high critical temperature (96.7 °C) lets heat pumps deliver flow temperatures of 70–75 °C, ideal for radiator retrofits and hot water. It is classed A3 (highly flammable), so units use small charges, spark-free components and are usually built as outdoor monoblocks.