Should I use a mini-split?

For most California ADUs, yes — a ductless mini-split heat pump is the default and usually the smartest choice. It heats and cools in one all-electric unit, eliminates ductwork (preserving precious ceiling height in a small building), runs very efficiently, and is the path of least resistance through Title 24 plan check.

When a mini-split is the right call

• Limited ceiling height or no attic/chase space for ducts — the mini-split's small line set needs only a 3-inch wall penetration.
• You want room-by-room control — a multi-zone system lets an occupied bedroom and an empty living room hold different setpoints.
• Your city has an all-electric reach code — mini-splits contain no combustion and comply directly.
• You want to maximize Title 24 margin — quality mini-splits typically exceed minimum SEER2/HSPF2 thresholds by a wide margin, and eliminating ducts removes duct-leakage losses that often cause HERS test failures.

Single-zone vs. multi-zone

A single-zone system pairs one outdoor condenser with one indoor head — ideal for studios and open-plan ADUs under roughly 600 SF, where air circulates freely. A multi-zone system feeds two, three, or more heads from one condenser, with each enclosed bedroom typically getting its own head so it holds temperature with the door closed. The engineer sizes the condenser and each head from per-room load calculations rather than installing identical heads everywhere.

Honest trade-offs

• A wall-mounted head is visible in each conditioned room (ceiling-cassette and concealed-duct heads are alternatives).
• Multi-zone installed cost runs higher than a single head.
• Each enclosed room generally needs its own head, so head count tracks the floor plan.

If the trade-offs of visible heads or multiple zones are a concern in a larger, multi-room ADU, a ducted heat pump with a central air handler is the main alternative — but for compact ADUs, the ductless mini-split is hard to beat.

Decision checklist

1. Count the separately enclosed habitable rooms — bedrooms each want a zone.
2. Run a per-room Manual J for head sizing.
3. Confirm the condenser's total capacity covers the connected heads.
4. Verify line-set routing and condenser setbacks are feasible on your site.
5. Check that every habitable room receives heat (a code requirement).

System availability and sizing vary by project and brand, and local rules vary by jurisdiction — confirm with your local building department. Our mechanical plans specify the exact heads, condenser, and routing with the Manual J included. See pricing or order here.