Ductless Mini-Split Installation in San Diego, for the Rooms Ducts Never Reached

A ductless mini-split is a heat pump split into two parts: an outdoor unit with the compressor and condenser coil, and one or more indoor units (heads) that each condition the room they hang in. The two are connected by a refrigerant line set, a control cable and a condensate drain that pass through a single hole in the wall. There is no ductwork, no air handler in the attic, and no combustion. The compressor is inverter-driven, so it ramps up and down to hold a setpoint instead of switching on and off.

Where mini-splits fit in San Diego

• ADUs and garage conversions. The county's ADU boom put a lot of 400–800 sq ft units on lots in Clairemont, La Mesa, Encinitas and Chula Vista. A single-zone mini-split is the standard way to condition one without tying into the main house system.
• Additions and bonus rooms. A room added over the garage or off the back of a 1970s tract home usually has no duct capacity. A dedicated head solves it without reworking the trunk line.
• Beach and older homes without ducts. Homes in Ocean Beach, Pacific Beach, North Park and Kensington were built with a wall furnace and no ducts. Mini-splits add cooling and cleaner heat without opening ceilings.
• The one hot room. A west-facing primary bedroom in Scripps Ranch or Santee that the central system cannot keep up with on an inland heat wave. One head, one circuit, done.
• Garages, workshops and home offices. Spaces that were never meant to be conditioned and should not be tied to the house ducts.

Single-zone vs. multi-zone

A single-zone system is one outdoor unit and one head, the simplest and most efficient arrangement. A multi-zone system runs two to five heads from one outdoor unit, saving outdoor space and electrical work. Multi-zone has two catches: every head has a minimum output, so a small bedroom on a big outdoor unit can get too much air, and the outdoor unit modulates for the combined load, so one head running alone is less efficient than it would be on its own system. For rooms on opposite ends of the house, two single-zone systems are often the better design.

Efficiency

Mini-splits carry some of the highest SEER2 and HSPF2 ratings available, partly because the inverter compressor runs at partial speed most of the time and partly because there are no duct losses at all. In a coastal Zone 7 home with modest cooling hours, the efficiency premium matters less than the fact that you are conditioning only the room you are in. Inland, where a Zone 10 bedroom needs cooling from May to October, the savings are real. See what SEER2 means.

Aesthetics and placement

The wall-mounted head is what most people picture, and it is the least expensive and easiest to service. It should sit high on a wall with a clear throw across the room, not above a bed or blowing directly on a desk. The line set runs outside in a painted line-hide cover or inside a wall cavity. If a wall head is not acceptable, ceiling cassettes recess into the ceiling, floor consoles sit under a window like a radiator, and a slim ducted unit hides in a closet and serves two or three rooms through short duct runs. Outdoor units go on a pad or wall brackets, with clearance for airflow and service and away from bedroom windows.

If you are conditioning a whole house rather than a few rooms, compare with a ducted heat pump before deciding.