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How to Install a Whole-House Ductless System

Ask This Old House plumbing and heating expert Richard Trethewey shows a style of ductless heat pump that can be used to heat and cool an entire house


  1. Installing a whole-house heat pump is best left to a professional contractor. The contractor should run a heat load calculation to determine the correct sizing of the overall system.
  2. A wall-mounted ductless heat pump is a good solution for open areas like entertaining areas, bonus rooms, or open floor plans.
  3. Outdoor units can be sized to accommodate multiple zones of heating and cooling.
  4. In snowy climates, the outdoor unit should be mounted above the snow line.
  5. Refrigerant tubing connects the outdoor unit to the indoor units via a branch box which can connect five indoor units with individual refrigerant lines.
  6. Ductless units can be attached to duct work to feed conditioned air into the living space. Each unit requires two refrigerant connections, a drain line to remove condensate, a supply duct to bring conditioned air to the living space, and a return duct to bring the air back to be heated or cooled.
  7. Each zone has its own programmable thermostat.


All of the heating and cooling equipment, including the outdoor condenser, indoor wall-mounted unit, and indoor air handlers are manufactured by Mitsubishi Electric Cooling & Heat.

Expert advice with this installation was provided by NETR Inc.