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Ductless HVAC Glossary of Terms

If you’re exploring just how well a Mitsubishi Electric Cooling & Heating ductless air conditioner or heater can serve your space, there are some terms you need to know. Here are the most common ones you’ll come across as you research this highly efficient comfort technology.

Air Conditioner

An air conditioner is equipment that cools the air in a home, room or building by regulating the temperature and humidity.


BTU refers to British thermal unit, which is the degree of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit. In the HVAC industry, BTU/h is a unit of measurement that refers to the amount of heat generated per hour.

Load or Capacity

A load or capacity is a refrigeration rating system that is measured in BTU/h.


In an air conditioner, the compressor acts as the pump of the unit. It takes the incoming refrigerant as a gas, compresses it and changes it into a liquid. The compressor is located outside, and it helps move the liquid into the indoor unit.

External Static Pressure

External static pressure, or ESP, is the measurement of static pressure losses from ducts, dampers, grilles, fittings and other components that are in the airstream.

Heat Pumps

A heat pump is an energy-efficient system that provides heating and cooling. In the summer, it acts as an air conditioner, and in the winter, it draws ambient air from the outside and moves the warm air inside.


HSPF stands for heating system performance factor, which measures the efficiency of a heat pump during the winter.


HVAC stands for heating, ventilation and air conditioning.

Indoor Unit

The indoor unit is the air handler of an air-conditioning system. It contains evaporator coils, a fan, filters and a remote receiver. This unit blows the cooled and conditioned air into the rooms.

INVERTER Technology

Mitsubishi Electric offers superior indoor climate control by designing products that use INVERTER technology. This feature allows the system to sense changes in temperature and to respond to these temperature variations. By generating the right amount of power to maintain a comfortable temperature, the system conserves energy. Mitsubishi Electric’s P-Series, CITY-MULTI®, MUY, MUZ and MXZ systems all use INVERTER technology.


The microprocessor is an electronic component that consists of integrated circuits. In an air conditioner, the microprocessor uses computerized technology to monitor and control the unit's performance.

Outdoor Unit

The outdoor unit contains the compressor, condenser coil, condenser unit, fan and circuit board. It takes refrigerant from its gaseous state and pumps compressed liquid to the indoor unit.


The refrigerant is the substance used in air conditioners that is responsible for helping to cool the air. It exists in both gaseous and liquid states. Mitsubishi Electric products use R410A, which is environmentally friendly.

Refrigerant Lines

Made from insulated copper tubing, the refrigerant lines carry refrigerant between the indoor and outdoor units.


SEER is seasonal energy efficiency ratio. This is used to measure the energy efficiency of a heat pump or air conditioner during warm weather. A higher number means that the unit is more energy efficient.

Split-Ductless System

A split-ductless system contains both an outdoor and indoor unit. They are connected by refrigerant pipes, but there is usually no ductwork. However, limited ductwork can be installed for ventilation.

Split-Ducted System

A split-ducted system has an indoor and an outdoor unit. The units are connected by refrigerant pipes, and the system uses ducts to carry the air.

Split-Zoning System

A split-zoning system consists of an indoor and outdoor unit, and they are connected by refrigerant pipes. The system is designed to heat and cool specific zones inside the building, which allows for superior climate control. All of the zones are independent from each other.


A zone is made up of one or more rooms in the same building, and each zone has its own temperature setting. All zones are independent from each other.

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