Common HVAC Unit Conversion Factors

A quick reference for frequently used unit conversions in HVAC calculations.

Essential HVAC Conversions

Accurate unit conversion is fundamental in HVAC design, installation, and service. Errors in conversion can lead to incorrect calculations, undersized or oversized equipment, and inefficient system operation. This page provides a quick reference for some of the most common conversions encountered by HVAC professionals.

While many of our dedicated calculators handle these conversions internally, having a basic understanding of these factors is beneficial for quick estimates and comprehending technical data.

Temperature

  • Celsius (°C) to Fahrenheit (°F): °F = (°C × 9/5) + 32
  • Fahrenheit (°F) to Celsius (°C): °C = (°F - 32) × 5/9

Pressure

  • 1 pound per square inch (psi) ≈ 6.895 kilopascals (kPa)
  • 1 psi ≈ 2.036 inches of mercury (inHg) at 32°F
  • 1 psi ≈ 27.7 inches of water column (in. w.c.) at 60°F
  • 1 inch of water column (in. w.c.) ≈ 249.089 Pascals (Pa)
  • 1 standard atmosphere (atm) = 101.325 kPa = 14.696 psi

Power / Heat Flow Rate

  • 1 British Thermal Unit per hour (BTU/hr) ≈ 0.293071 Watts (W)
  • 1 Ton of refrigeration = 12,000 BTU/hr
  • 1 Ton of refrigeration = 3.51685 kilowatts (kW)
  • 1 kilowatt (kW) ≈ 3412.14 BTU/hr
  • 1 horsepower (hp) (mechanical) ≈ 745.7 Watts
  • 1 horsepower (hp) (electrical, motor output) ≈ 746 Watts

Airflow

  • 1 cubic foot per minute (CFM) ≈ 0.47195 liters per second (L/s)
  • 1 CFM ≈ 1.699 cubic meters per hour (m³/h)

Length & Area

  • 1 foot (ft) = 0.3048 meters (m)
  • 1 inch (in) = 25.4 millimeters (mm) = 2.54 centimeters (cm)
  • 1 square foot (sq ft) ≈ 0.0929 square meters (m²)

Energy

  • 1 kilowatt-hour (kWh) = 3412 BTU
  • 1 Therm = 100,000 BTU

These conversion factors are commonly used approximations. For highly precise scientific or engineering work, refer to official standards or more detailed conversion tables.