Btu/h
Heating or cooling capacity expressed as a rate of heat transfer per hour.
Tons
Cooling-capacity shorthand; one nominal ton equals 12,000 Btu/h.
CFM
Air volume in cubic feet per minute.
FPM
Air velocity in feet per minute.
Inches of Water Column
A pressure unit commonly used for duct static pressure and gas pressure.
PSI
Pounds per square inch, commonly used for refrigerant, water and gas pressure.
Microns
A deep-vacuum measurement used during refrigeration-system evacuation.
Temperature Rise
The increase in air temperature across heating equipment.
Temperature Split
The difference between return- and supply-air temperatures across HVAC equipment.
Superheat
How far refrigerant vapor temperature is above saturation temperature.
Subcooling
How far refrigerant liquid temperature is below saturation temperature.
Relative Humidity
Air moisture expressed relative to the maximum possible at that temperature.
Dew Point
The temperature at which moisture begins condensing from air.
Wet Bulb
A temperature influenced by evaporative cooling and moisture content.
Dry Bulb
Ordinary air temperature.
Amp Draw
Electrical current consumed by a load during operation.
Voltage
Electrical potential difference between two points.
Resistance
Opposition to electrical current, measured in ohms.
Watt
A unit of electrical power.
VA
Volt-amperes, a unit of apparent AC electrical power.
RPM
Rotational speed in revolutions per minute.