Photo by James Dulley
Mini-split heat pumps are small enough that both the indoor unit and outdoor condenser/compressor can be mounted on high walls, allowing for plenty of clearance underneath.
Q: We have a new room addition and an upstairs bedroom that our central air conditioner doesn’t cool very well. Should we install window air conditioners or a mini‑split system?
A: This is a common problem for second-floor rooms and add-ons. Warm air tends to rise to upper floors through cracks, gaps and stairwells. Room additions are sometimes not connected to existing ductwork or served efficiently by a home’s current heating/cooling system.
The choice between installing a mini-split heat pump or a window air conditioner depends on your needs. A window air conditioner can provide extra cooling in a room at a low initial cost, when energy efficiency is not the primary concern. Mini-split heat pumps are ductless systems that can cool or heat individual rooms, with the added benefits of quieter operation and increased efficiency, but at a higher up-front price.
The main drawback for mini-split heat pumps is cost. A window unit generally sells for less than $300; mini-splits can run to more than $1,000, plus the cost of installation. But in homes that rely on electric-resistance heating methods or where aging ductwork may be losing its efficiency, mini-split systems can help reduce monthly electric bills.
With a window air conditioner, all the components—compressor, air circulation fan, condenser fan—are in the cabinet mounted in the window. Although it is insulated against heat flow and sound, it is not ideal for energy efficiency. Newer versions are fairly quiet but still may be noisy while you sleep.
A mini-split system is similar to a central air conditioner or heat pump, with the condenser fan, coils and compressor in an outdoor unit, which is flat and small. It can be mounted high on an exterior wall and up to 100 feet away from the room or group of rooms to be cooled or heated. This virtually eliminates indoor noise from these components.
The indoor cooling coil is mounted in a fan unit on the wall or ceiling of the room where it’s needed. It’s connected to the outdoor unit by refrigerant and electric lines. Only a 3-inch-diameter hole needs to be cut through the wall; the condensate drain from the evaporator coils can go out through the same hole. Unlike a window unit, mini-splits can’t be moved once installed.
Mini-split systems can cool an entire house by installing indoor wall units in several rooms. The conditioned air circulates naturally throughout the house.
A mini-split unit also allows for zone cooling of your house, which can lower your electric bill. There’s no need to keep the downstairs cool all night while you’re sleeping upstairs. The mini-split system lets you set the central heat-pump thermostat higher at night, so you’re not paying to cool unused spaces.
Innovative inverter compressor technology in some mini-split systems lets the compressor run at variable speeds—when a room reaches your selected thermostat setting, the inverter compressor speed slows to maintain that temperature. Newer models also offer options for remote control and a dehumidification setting. An HVAC professional can help you decide if a mini-split is suited to your needs.
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More information on ductless cooling systems can be found at energy.gov, or go to energystar.gov.
The following companies offer mini-split air conditioners/heat pumps:
Carrier, (800) 227-7437
Fujitsu General, (888) 888-3424
LG, (800) 423-4164
Mitsubishi Electric, (800) 433-4822
Samsung, (888) 699-6067