HVAC is easy to leave until late in an ADU project. That is usually when it gets expensive: the equipment doesn't fit where the plans assumed, the panel can't carry the load, or the Title 24 report doesn't match what gets installed. Here is what to settle early.
Pick the system type during design
Most ADUs end up with one of these:
- Ductless mini-split heat pumps. Compact, efficient, and no duct space needed. Common for studios and one-bedroom units. Larger layouts may need more than one indoor unit.
- Small ducted heat pumps. A compact air handler with short duct runs. Useful when you want concealed vents and even temperatures in a multi-room layout.
The right choice depends on the floor plan, ceiling heights, where an outdoor unit can go, and the owner's preferences. A room-by-room load calculation is the starting point. Small, well-insulated units are easy to oversize, and an oversized system cycles on and off and controls humidity poorly.
Title 24 is part of the design, not an afterthought
California's energy code (Title 24, Part 6) applies to new ADUs. Your Title 24 report is prepared from specific assumptions about equipment efficiency, duct location and design, and ventilation. If the installed system differs from the report, you may need revisions before final inspection.
Practical steps:
- Get equipment specs to your Title 24 consultant before the report is finalized.
- Find out which HERS verifications your project needs and who is scheduling them.
- Plan for whole-house mechanical ventilation, which the energy code requires in new dwelling units.
Plan electrical capacity early
ADUs often share electrical service with the main house. Heat pumps, a heat pump water heater, an induction range, and an EV charger can add up. Give your electrician the HVAC electrical requirements early so the panel and service size are planned once.
Coordinate the schedule
HVAC touches several stages of the build:
- Rough-in after framing: line sets, ducts, condensate drains, and wall penetrations before insulation and drywall.
- Trim-out after finishes: indoor units, grilles, and the outdoor unit.
- Start-up and commissioning, then HERS verification and final inspection.
Missing the rough-in window means opening walls later. Lock in dates with your HVAC contractor when you set the framing schedule.
Things that are easy to miss
- Outdoor unit location. Setbacks, noise near neighbors' windows, and service access.
- Condensate drainage. Where the water goes, especially for wall-mounted indoor units.
- Line-set routing. Exterior line-set covers look much better when planned, not improvised.
If you are planning an ADU or SB 9 project in Contra Costa or Alameda County, send us the details through our builder and ADU inquiry form.