Heat pumps are a bit of a mysatery to many Boston homeowners. For decades, centralized systems have remained the unchallenged heating and cooling default. With all of the ductwork removed and replaced with a comparably small indoor handling unit, how can heat pumps achieve anything close to a conventional unit?

Well, despite their clear differences, these temperature control solutions share some similarities. Here, we’ll take a deep dive into the functioning of a ductless HVAC system with special attention paid to the important role refrigerant plays.

What is refrigerant and how is it used in an HVAC system?

Refrigerant is a chemical substance used for its ability to absorb heat from the environment surrounding it. It’s commonly used in freezers, refrigerators, and air conditioners to achieve these temperature changes. When being used, refrigerant is constantly changing from a gas to a liquid and repeating the process.

In both centralized and ductless HVAC systems, refrigerant is responsible for transferring heat to and from the inside of a home. When ductless is cooling a room, it carries heat from the indoor unit to the outdoor unit where it’s released into the air. Conversely, when in heating mode, the refrigerant absorbs heat from the outdoor air and releases it inside.

How does a refrigerant flow through a ductless system?

Now that you have a better understanding of what refrigerant does, we’ll follow its path through a ductless HVAC system. We’ll break down the process into four different stages: the evaporator coil, compressor, condenser, and expansion valve. To keep things simple, we’ll focus on what refrigerant does when in air conditioning mode.

Evaporator Coil

In an indoor handling unit, the refrigerant flows through the evaporator coil. As air passes through the heat pump and over these coils, the refrigerant absorbs heat from it. Humidity is also removed from the air through the same process. At this point, the refrigerant is cold and in gas form. After absorbing heat from the indoor air, it’s pushed through a connecting tube towards the compressor.


As you might be able to guess from its name, this component of a ductless system compresses the refrigerant, resulting in an increase in temperature and pressure. This compression continues to push the refrigerant through the system while making it easier for the second heat transfer to occur. After the compressor, the refrigerant flows to the outdoor unit.


Once outside, refrigerant heads straight for the condenser which operates in a similar fashion to the evaporator coil – just in reverse. Here, the refrigerant releases heat into the outside environment as ambient air is blown over the condenser coils. The temperature difference between the air being blown and the refrigerant causes the hotter refrigerant to emit heat.

Expansion Valve

Before the refrigerant can flow back into the indoor handling units, its temperature and pressure need to be reduced. The expansion valve essentially reverses what the compressor achieved by returning the refrigerant to a liquid state. From here, the refrigerant is pushed to the evaporator coils, and the process repeats.

How does refrigerant work when heating a home?

In order to raise the temperature in a home, the process we just discussed is completely flipped. Ductless mini-splits have reversing valves that allow refrigerant to flow in both directions. When switched to heating mode, refrigerant pulls heat from the outdoor air and emits it inside.

In both cases, heat pumps are relying on heat’s tendency to flow towards cooler areas in order to function properly. Refrigerant is simply the means of transferring that energy from the indoors to the outdoors and vice versa.

Advantages of a Ductless System

Although refrigerant functions similarly for both centralized and ductless HVAC systems, there are inherent advantages to using mini-splits. Here are just a few of the benefits Boston homeowners can look forward to when using ductless heat pumps:

If you’re interested in learning more about how a ductless HVAC system can solve your heating and cooling needs while improving your home’s energy efficiency, you’re in the right spot. New England Ductless is a leading provider of ductless systems and maintenance solutions in the Boston area. Feel free to contact us for an in-home consultation with one of our highly skilled and experienced installation experts.

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