If your house doesn’t have ductwork for central heating and air conditioning, you may choose a window unit or ductless air conditioning and avoid ductwork. A ductless air conditioner, also called a mini-split system, requires an inside unit that connects to an exterior unit. Two conduit lines connect the units, with refrigerant running through one line and condensation leaving the indoor unit through the other line. The mini-split system works well for a single-room oasis or zone control.
EnviroMaster, Frederich, Frigidaire, GLEE, Goodman and several other companies manufacture a mini-split or ductless air-conditioning system with 9,000 British thermal units, or Btu. Finding units that are less than three-quarters of a ton is a challenge. Mitsubishi makes a half-ton or 6,000 Btu ductless unit called Mr. Slim. Daikin manufactures a unit that is 8,500 Btu. Carrier makes an X Power unit that is 8,600 Btu shown on the U.S. Department of Energy website, Energy Savers. The Air Conditioning, Heating and Refrigeration Institute website provides a table of energy-efficient mini-split systems with Btu and seasonal energy-efficiency ratings. The AHRI type is RCU-A-CB-O for mini-split units.
The Btu rating isn’t the only consideration when purchasing a mini-split air-conditioning system. Air Conditioning Contractors of America provides Manual J for calculating the size of your air-conditioning unit. This calculation considers the orientation of your house, as well as your location, and determines the size of the unit you need. Air-conditioning units have a seasonal energy-efficiency rating to compare one unit to another. The highest SEER number provides the most efficiency. Frigidaire reports that their 9,000 Btu mini-split system cools approximately 400 square feet. Manual J considers the local climate, the size of the area to be conditioned, the window area, lighting and number of occupants.
The initial purchase price of the mini-split system is high. Ductless air-conditioning hardware and installation costs are greater per square foot of cooling than central air through available ductwork or window-unit installation. Mini-split air conditioners avoid the energy loss from ductwork, estimated as high as 30 percent by the U.S. Department of Energy. You can condition a single area or room with a small mini-split system, and save energy and the cost of central air. The mini-split system is more secure than a window unit that provides a potential opening for burglars.
The ductless system requires a small hole from inside to outside the house to run the conduit. Location of the indoor unit on an outside wall makes installation easier. According to the U.S. Department of Energy, many older air-conditioning systems are oversized. Have calculations performed with Manual J specifications to determine the size unit you need, and choose a ductless system with a high SEER rating for energy efficiency and economy. A 6,000 to 9,000 Btu unit may be all you need for a single room or living area, but larger ductless units are also available.
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