Ductless air conditioners are called “mini-split” systems because they are similar to a regular ducted split central air conditioner, only on a smaller scale. A split system means that the compressor/condenser unit is located outdoors and “split” from the indoor cooling coils/blower. Just a small three-inch diameter hole is cut in the wall to run the tiny refrigerant lines and electric wires to the indoor cooling units.

With the compressor outdoors and an indoor cooling unit mounted high on a wall or ceiling, they are super-quiet (sounds like a “whoosh”). These units are typically even quieter than many ducted central air conditioners. In a central unit, huge amounts of air must wind through complex ducts with many bends and shape changes, all of which contribute to noise.

Mini-split ductless air-conditioners are a preferred option to trying to use several room air conditioners to cool an entire house. Window units may block the window.

Nowadays the efficiency ratings of ductless systems (SEER from 10 to 19) are as high or higher as the top-of-the-line central air conditioner (SEER up to 16), and they can still be more efficient than window, wall and even central units. Since mini splits have no ducts, they avoid the energy losses associated with ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for space conditioning, especially if the ducts are in a unconditioned space such as an attic.

Heat pump models are also available for keeping warm. If you hate that first shot of chilly air in the winter each time the furnace or heat pump blower starts, select a ductless model with a soft, slow start and a pre-heater for the air. For colder climates, some of the heat pump models also have backup electric resistance heat.

Ductless, mini split-system air-conditioners and heat pumps (mini splits) have numerous potential applications in residential, commercial, and institutional buildings. The most common applications are in multifamily housing or as retrofit add-ons to houses with “non-ducted” heating systems, such as hydronic (hot water heat), radiant panels, and space heaters (wood, kerosene, propane).

They can also 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. Applications in other types of buildings include: recording studios, school classrooms; perimeter cooling for office buildings; additional cooling for restaurant kitchens; and cooling for small offices within larger spaces, such as arenas, warehouses, and auditoriums.

The primary disadvantage of mini splits is their cost. Although, costs have decreased dramatically during the past few years, such systems can cost about $600-$2,000 per ton (12,000 Btu per hour) of cooling capacity. This is about 10% more than central systems (not including ductwork) and may cost twice as much as window units of similar capacity.

The installer must also correctly size each indoor unit and judge the best location for its installation. Oversized or incorrectly located air-handlers often result in short-cycling, which wastes energy and does not provide proper temperature or humidity control. Too large a system is also more expensive to buy and operate.

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