Ductless Mini-Splits for ADUs: A Los Angeles Permitting Guide
Adding an ADU or garage conversion in LA? Here's everything we've learned about sizing, permitting, and installing ductless systems to pass inspection the first time.
Why mini-splits are the right choice for LA ADUs
Accessory Dwelling Units — backyard cottages, garage conversions, over-garage units — are being built across Los Angeles at record pace. For HVAC, ductless mini-splits are almost always the right answer: they require no ductwork (which ADUs usually can't accommodate), they can be permitted alongside the ADU, and they're highly efficient.
Sizing your ADU mini-split
Rule of thumb: a 400 sq ft ADU needs about 9,000 BTU (¾ ton). But LA's climate means solar gain is significant, and a garage conversion with west-facing windows may need 12,000 BTU for the same size. We do Manual J calculations for every ADU — don't let anyone size your system by floor area alone.
LA permitting requirements for ADU HVAC
Los Angeles requires a mechanical permit for any new HVAC system, including mini-splits in ADUs. Here's what's involved:
- Mechanical permit — required for the mini-split installation. We apply on your behalf.
- Title 24 compliance — California requires a Title 24 energy compliance calculation for new construction and significant renovations. We provide this documentation.
- Electrical permit — the outdoor unit requires a dedicated circuit. Often coordinated with the ADU's main electrical permit.
- Inspection — LA DBS schedules an inspection after rough-in and final. We coordinate the timing with your project schedule.
What the installation actually looks like
For a standard ADU mini-split:
- Indoor head unit mounted on wall (high on the room's longest wall, typically)
- Refrigerant lines run through a small penetration to the outdoor unit
- Outdoor unit mounted on a pad or wall bracket outside the ADU
- Electrical from the sub-panel to the outdoor unit
The whole installation typically takes 4–6 hours for a single-zone system. Add a half-day for permit application coordination. Most ADU projects complete HVAC in a single day.
Brands we recommend for ADUs
Mitsubishi and Daikin are our first recommendations for ADUs — both have 12-year compressor warranties with registration, both are HEEHRA-eligible, and both have excellent parts availability. For tighter budgets, LG and Carrier provide solid performance at a lower installed cost.
Ready to size your ADU? Contact us for a free consultation — we'll size the system, quote the installation, and handle every permit.
Ready to get started?
Free in-home consultation with any new or replacement HVAC system, or any service / repair over $200. We answer the phone 24/7.