Definition
Zone HVAC system with outdoor compressor and indoor head(s) — no ductwork; common for additions, ADUs, and baseboard replacement in Washington.
When is ductless the right call instead of a ducted system?
When the house has no ducts and adding them would mean tearing into finished walls and ceilings: pre-war homes on radiators or wall heaters, homes on electric baseboard, additions, converted garages, and ADUs. One outdoor unit can feed one to five indoor heads, each with its own thermostat — real zoning, so bedrooms and living spaces stop fighting over one setting.
What are the trade-offs?
Each indoor head is visible on a wall or ceiling, and filters live in each head rather than one return. Whole-home coverage of a larger house can take several heads, at which point a ducted heat pump may price similarly if ducts already exist. The efficiency story is strong either way — no duct losses, which typically waste 20–30% of heated air in leaky duct runs.
How many indoor heads do you actually need?
Fewer than most first sketches. Each head is sized to its zone, and open-plan spaces usually want one well-placed larger head instead of two small ones. Bedrooms that share a hallway can often be served by a single head plus transfer airflow. Over-heading raises cost and hurts efficiency — the right plan comes from a room-by-room load look, not a per-room default.
In the Puget Sound
Ductless is the workhorse retrofit for Seattle's baseboard-heated mid-century homes: heat and first-time air conditioning in one project, without opening original plaster.
Related terms
Go deeper on Ductless mini-split
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Trade: Heating & Air