Facts About Split Air Conditioning Systems

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Facts about split air conditioning systems, also known as min splits. This article discusses the advantages and disadvantages of this type of system for cooling your home or business.

A fairly recent addition to residential air conditioning (AC) systems is the ductless, split air conditioner system, sometimes referred to as mini splits. They have been used is commercial, institutional, and retail buildings since the early 1990’s. The most common applications are in multifamily housing or as retrofit add-ons to houses with "non-ducted" cooling or heating systems. Split air conditioners can be a good choice for room additions and small apartments, where extending or installing distribution ductwork for a central air-conditioner or heating systems is not feasible or would mean increasing the cooling capacity of the central system.

Split AC units are not the same as window air conditioners which are a packaged unit. Window AC units have all of the components in one case and are noisy and have condensate running out of the unit to the outside.

System Overview

A split AC system has two components, an indoor air handling unit, usually wall mounted, and an outdoor condensing unit. Refrigerant piping connects the two components to one another so that heat is removed from the indoor space and rejected to the outside. Most manufacturers make heat pump units that will also heat the home in the winter. The units range in size from 9,000 to 30,000 Btu.

A. Condensate line

B. Liquid Line (Refrigerant)

C. Suction Line (Refrigerant)

D. Control Wire

E. Flare Fittings (Refrigerant)

F. Electrical Feed

Split Air Conditioning System Diagram


The main advantages of split AC installations are their small size and flexibility for zoning individual rooms. A split air conditioner can have several indoor air handling units or zones connected to one outdoor unit. The number depends on how much heating or cooling is required for the building or each zone. Each zone will have its own thermostat that can be programmed or turned on when the room is occupied. This operation profile will save energy and money.

The units are fairly easy to install since there is no ductwork to run through the home. The indoor unit can be as far as 100 feet away from the outdoor condenser and there only space required is a three inch hole through a wall for the insulated copper tubing and control wiring. The condenser unit can also be located on a flat section of roof if available.

Duct losses can account for more than 30% of energy consumption for space cooling, more if the ducts are in an unconditioned space such as an attic. Losses for split AC systems range from 1% to 5%.

The units can be located where they are needed most and operate quietly. Some units operate at 22dB which is about the level of someone whispering.

Energy is saved since smaller fan motors are used and individual units run at different times. In traditional central AC systems, the whole house is cooled when a thermostat in one location is calling for cooling.

The outdoor units are quieter than traditional central AC systems. The compressors are also smaller and would be less expensive to replace if required.

Most units come with a remote control as well as a wall mounted thermostat.

Aesthetics are improved over window units and no windows need to be blocked.

In comparison to other add-on systems, split AC systems offer more flexibility in interior design options. The indoor air handlers, sometimes called cassettes, can be suspended from a ceiling, mounted flush into a drop ceiling, but are usually hung on a wall. Some manufacturers make units that can be installed in a closet where only the supply and return grilles are visible. Most wall mounted split AC units are about 8 to 9 inches deep.

You may be eligible for a Federal Tax Rebate or local rebates from your utility provider or State government if your unit meets their energy efficiency requirements.


The primary disadvantage of split air conditioners is their higher initial cost per ton of cooling capacity. This higher cost can be offset by energy savings within a year or two from reduced energy usage from duct losses.

The units need to be installed be a qualified technician since refrigerant piping needs to be installed between the air handler and the condenser. It is possible to mount the units and run the refrigerant lines and have an HVAC technician pump down the system and make the final connections.

Another concern is that the indoor cassette will produce condensate that needs to be removed. Most units have an internal condensate receiver and pump that can lift the condensate about 10 feet. For wall mounted units this is more than enough to pump the condensate through vinyl tubing that can be run to the nearest drain. If a basement is available, the outlet of the condensate pump can be run to a sump pit or utility sink. Another option is to run the tubing to an outside wall and pump the condensate onto the ground.

A separate outlet or electrical connection will need to be installed for each indoor unit, which adds to the installation costs.

Slightly higher maintenance requirements if you have multiple units installed. Each unit has a filter that must be cleaned periodically and more components to fail. Since the units are distributed, you won’t lose the cooling for the entire home.


Split Air Conditioning systems are an ideal choice when renovating or remodeling your home or when you convert a garage, basement, or attic into a room or in homes that don’t have ductwork already installed. As long as you are aware of the options and the disadvantages that you need to overcome in your final design, these systems can offer improved comfort and energy saving for years.



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Posted on Apr 28, 2010