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Air Conditioning With a Ductless Mini Split: How Does It Work?

Ductless systems offer homeowners more flexibility. A ductless mini split is one of the more modern and innovative ways for air conditioning a home or building. These systems use the same principles as central air conditioners, but do so without needing ductwork to deliver the air. Mini splits are used as complete cooling systems, or can be used in a space that would be hard to cool by extending ductwork. Mini splits that are heat pumps can also warm a space during cold weather. 


A ductless system has two primary components – an indoor air handler (or two or more) and an outdoor condenser/compressor. The air handler contains an evaporator coil and the fan, and the outside unit houses the condensing coil, a fan and the compressor. A narrow pipe, or conduit, contains the refrigerant, the drainpipe and the power supply. The conduit connects to the condensing unit and the air handler(s) and requires just a three-inch hole running through an exterior wall.

How it Cools

The compressor pressurizes hot gaseous refrigerant, turning it into a liquid. It sends it into the evaporator coil inside the indoor air handler, and the fan blows interior air over it. The liquid refrigerant picks up the heat from the passing air, which cools the air and warms the refrigerant, turning it back into a gas. The refrigerant returns to the compressor where it's put under pressure again, releasing the heat energy into the outside air, and then returns to the air handler until the room reaches the thermostat's setting. 

As part of the air conditioning process, the humidity in the air condenses when it passes over the evaporator coil, and the resulting water drains into the drainpipe inside the conduit and is released outdoors. 

The air handler contain a fan that blows the conditioned air into the room. It may be outfitted with a variable speed blow motor that can adjust the delivery of cool air to meet circumstances in the home. They also filter the incoming air; all Mitsubishi mini splits have advanced filtration systems that trap smaller particles to help improve indoor air quality. These filters can be cleaned and have a long system lifetime. 

How it Differs from a Central Cooling System

A mini split air conditioning system differs from a central A/C in that it doesn't use ductwork. A central air conditioner or heat pump delivers air through a network of ducts. When ductless systems are installed, the HVAC professional will find the best position in the room for thorough air delivery so that it provides even cooling. There's no need for a bulky air handler unit inside the home, and the lack of ducts allows for easy furniture placement. 

Since they don't use ducts, mini splits don't waste as much energy as central systems. They must meet the same minimum SEER (seasonal energy efficiency ratio) requirements that central systems do, but they have no ductwork losses, either through leakage or thermal losses. Depending on the age and condition of your ductwork, you could see considerably lower costs running such a system.

Larger mini split systems can support up to four air handlers, each of which connects to the outdoor condenser/compressor. Each has its own thermostat, so instead of cooling your entire home at once, you can cool just the spaces you're using, which is another energy saving benefit of using these for air conditioning. Since each air handler has its own temperature control, all handlers may not run at once, since heat gain throughout a home tends to vary. 

Installation Factors

Mini splits are easier to install than central systems, and some homeowners who have experience with improvement projects can do some of installation themselves, including installing a masonry slab where the outdoor condenser will sit and drilling the hole for the conduit. 

In order to protect the warranty and verify that the system will work as efficiently as possible, a licensed HVAC contractor should complete the process. He or she will place the condensing unit and air handler and connect the conduit. The installer also will show you how to maintain it periodically by checking and cleaning the filters, as well as the coils in the air handler and condenser. 

To learn more about air conditioning with a mini split, please contact us to find a Mitsubishi Electric Contractor near you. 

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