Mini Split (Ductless) Heat Pumps

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Ductless mini-split-system heat pumps (mini splits) make good 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 where extending or installing distribution duct-work is not feasible, and very efficient new homes that require only a small space conditioning system.

Like standard air-source heat pumps, mini splits have two main components — an outdoor compressor/condenser and an indoor air-handling unit. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and a condensate drain, links the outdoor and indoor units.

Advantages

The main advantages of mini splits are their small size and flexibility for zoning or heating and cooling individual rooms. Many models can have as many as four indoor air-handling units (for four zones or rooms) connected to one outdoor unit. The number depends on how much heating or cooling is required for the building or each zone (which in turn is affected by how well the building is insulated and air sealed). Each of the zones has its own thermostat, so you only need to condition occupied spaces.

Disadvantages

The cost of installing mini splits can be higher than some systems, although lower operating costs and rebates or other financial incentives  — offered in some areas — can help offset the initial expense.

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