Superheat & Subcooling Calculator

Quickly calculate actual superheat and subcooling for R-454B, R-32, R-410A, R-404A, R-448A, and R-507A HVAC and refrigeration equipment. Uses dew saturation for vapor superheat and bubble saturation for liquid subcooling.

SELECT REFRIGERANT

UNITS

R-454B (zeotropic): R-454B is a zeotropic blend with temperature glide of about 2.5 °F (1.5 °C) at typical evaporator and condenser conditions. When measuring subcooling on the liquid line, use the bubble saturation column. When measuring superheat on the suction line, use the dew saturation column.

View R-454B PT Chart

Suction Line Superheat

Uses Dew Point

Measured at the suction line service valve near the outdoor unit (or evaporator outlet).

Suction Pressure (psig)

Suction Line Temperature (°F)

ACTUAL SUPERHEAT12.0 °F

Dew Saturation Temperature: 40.0 °F

Formula: 52.0 °F − 40.0 °F = 12.0 °F

Liquid Line Subcooling

Uses Bubble Point

Measured at the liquid line service valve leaving the outdoor condenser coil.

Liquid Line Pressure (psig)

Liquid Line Temperature (°F)

ACTUAL SUBCOOLING12.0 °F

Bubble Saturation Temperature: 100.0 °F

Formula: 100.0 °F − 88.0 °F = 12.0 °F

How Superheat and Subcooling Work

Superheat measures how many degrees a refrigerant vapour is heated above its saturation (boiling) temperature after completely evaporating. It ensures liquid refrigerant does not flood back into the compressor. On systems with a thermal expansion valve (TXV), superheat is regulated automatically.

Subcooling measures how many degrees liquid refrigerant is cooled below its saturation (condensing) temperature after completely condensing. It ensures a pure liquid column reaches the metering device without vapour flash gas. TXV-metered systems are typically charged by subcooling.

Zeotropic refrigerant glide (R-454B & R-448A): Because zeotropic blends boil and condense across a range of temperatures (such as R-454B with ~2.5 °F glide and R-448A with ~9.5 °F glide), you must use the dew point for superheat (vapour state) and the bubble point for subcooling (liquid state). For pure R-32 and near-azeotropic R-410A and R-507A, the bubble and dew points are identical (or effectively identical).

psig = psia − 14.696 (standard atmospheric pressure at sea level).

Reference only. Follow the equipment manufacturer's charging instructions and data plate.