For decades, centralized HVAC systems have been the standard for Boston homeowners. Recently, more and more people are making the switch to ductless heating and cooling units. Although these modern systems have been used in Europe and Asia for years, they’re just starting to gain some attention in the US.

If you’ve been researching ductless mini-splits, you’ve probably come across unfamiliar terms and confusing acronyms. To help increase your understanding of mini-splits, we’ll provide a handy glossary of common terms. You can reference this whenever you come across a new term you’re not familiar with.

Air Filtration System

A device specifically designed to remove contaminants from air that’s circulated through an HVAC system.

Air Handler

The indoor unit of a ductless system responsible for moving air within the room.


Any substance causing allergic reactions such as dander, fungus, lint, mildew, mites, dust, pollen, pet hair, and bacteria.

British Thermal Units (BTU)

A unit of measurement used to determine how much heat an AC unit can remove from a zone each hour. In strict terms, it’s the amount of heat needed to increase one pound of water’s temperature by one degree Fahrenheit.

Coefficient of Performance (COP)

An energy-efficiency rating that describes the power output of an HVAC unit in ratio to ITS power input. Higher COPs point to units with higher energy efficiency while lower numbers might point to enhanced operating costs and energy consumption.

Cubic Feet Per Minute (CFM)

A unit of measurement used to determine the amount of air flowing through an HVAC system.


A component of a ductless system located in the outdoor unit that’s responsible for pressurizing refrigerant to ensure it continues flowing throughout the system.


The process of a ductless system switching on and off automatically in order to maintain optimum energy efficiency.


Channels responsible for distributing air in your home.

Heat Pump

An external unit of a ductless system responsible for heating and cooling your home.

High-Efficiency Particulate Absorbing (HEPA) Filter

A high-efficiency filter designed to remove smaller particles from the air as it passes through an HVAC system.

Heating Seasonal Performance Factor (HSPF)

Refers to the energy efficiency of a heat pump’s ability to increase the temperature in a zone.


A specialized device designed to add moisture to the air inside a home that’s too dry.

Indoor Air Quality (IAQ)

Refers to the quality of air within your home with regard to the comfort and safety of its occupants. Mini-splits are designed to filter out negative contaminants in order to increase the IAQ of your home.

Outdoor Unit

The external portion of a ductless system that sits on the outside of a home. It’s responsible for extracting heat from the air outside.


A critical substance used to transfer heat in a ductless heating system. It takes advantage of heat’s proclivity to travel towards warmer areas.

Seasonal Energy Efficiency Ratio (SEER)

This rating measures a ductless system’s cooling efficiency. Higher numbers point to improved efficiency.

Split System

A heating and cooling system that’s composed of at least one indoor unit and an outdoor unit. It’s also another name for ductless heat pumps or mini-split systems.

Variable-Speed Motor

A motor within a ductless heating system that controls the fan speed depending on your home’s heating and cooling needs. It works in tandem with a thermostat to maintain an ideal internal temperature while increasing energy efficiency.


A defined area in a home that is temperature-controlled by an indoor handling unit. Each zone is usually comprised of a single room.


Heating or cooling individual zones or spaces within a home separately instead of using a centralized AC unit.

If you’re interested in learning more about mini-splits or you want to schedule an appointment for installation, feel free to reach out to New England Ductless for more information. We’ve helped countless homeowners in Boston make the switch from centralized systems to ductless systems. We look forward to hearing from you!

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