kW is the total heat generated in kilowatts by all components
, and TF or TC represents the temperature rise over ambient air temperature in degrees F or degrees C respectively. Typical values for T are 18F or 10C, plus 25 percent added as a safety margin (i.e., 23F or 12.5C). If the ambient temperature gets too high, it may be difficult or impossible to maintain a safe operating temperature for the equipment in the cabinet without air conditioning.