Temperature Converter — °F to °C for HVAC Technicians

How to Convert Temperatures for HVAC/R Systems

Temperature conversions are an everyday necessity in the HVAC and refrigeration trades, particularly when dealing with imported equipment, reading manifold gauges, or calculating subcooling and superheat parameters. While the United States relies heavily on the Fahrenheit scale for residential thermostats and weather data, most scientific applications, including refrigerant saturation charts, often require precise conversions to Celsius or Kelvin.

Fahrenheit to Celsius Formula

To manually convert a temperature from Fahrenheit to Celsius, you must first subtract 32 from the Fahrenheit reading, and then multiply the result by 5/9. For example, to convert an indoor air temperature of 68°F to Celsius:

• Step 1: 68 - 32 = 36
• Step 2: 36 × (5/9) = 20°C

Celsius to Fahrenheit Formula

To convert from Celsius to Fahrenheit, the process is inverted. You multiply the Celsius temperature by 9/5 (or 1.8) and then add 32. For example, converting a chilled water supply temperature of 7°C to Fahrenheit:

• Step 1: 7 × 1.8 = 12.6
• Step 2: 12.6 + 32 = 44.6°F

The Role of Kelvin in Thermodynamics

The Kelvin scale is an absolute thermodynamic temperature scale used heavily in advanced mechanical engineering and psychrometric calculations. Absolute zero (0 K) is the theoretical temperature where all particle motion ceases, which equates to -273.15°C or -459.67°F. Unlike Fahrenheit and Celsius, the Kelvin scale does not use degrees—it is simply expressed as "Kelvins." To convert Celsius to Kelvin, simply add 273.15 to the Celsius value.