ADU and Room Addition HVAC in Contra Costa
Heating and cooling for ADUs, garages and additions
A backyard cottage, a converted garage or a new bedroom wing rarely works well tied onto the main house system. The existing furnace and ducts were sized for the original square footage, and stretching them usually leaves the new space hot in July and cold in January. We size heating and cooling for the ADU or addition on its own, most often with a ductless mini-split or a small ducted heat pump, and plan it around the Title 24 energy rules your permit will be checked against.
Why choose Blue Star
We have been a licensed C-20 heating and air contractor in Antioch since 2006, and we can work from plans as well as from finished rooms. On an ADU that means a room-by-room load calculation instead of a guess, a line set and condensate route that suits the layout, and an outdoor unit placed where it won't sit under a bedroom window. We coordinate with your builder or designer so the HVAC rough-in is done before insulation and drywall go up.
- Room-by-room load calculation
- Mini-split or ducted heat pump
- Title 24 and ECC coordination
- Outdoor unit placement plan
- Rough-in timed to your build
- Panel capacity check
Where we work
ADU projects look different across our area. In Concord, Pleasant Hill, Walnut Creek and Lafayette, many homes date to the 1960s and 70s, and the main electrical panel is often small, so we check capacity before choosing equipment. Brentwood and Oakley garage conversions face 100-degree summer afternoons, which makes insulation and correct sizing matter more than raw capacity. Bay Point, Discovery Bay and the other unincorporated communities permit through Contra Costa County, while Antioch, Pittsburg, Concord and Walnut Creek run their own building departments.
Major corridors
- SR-4
- SR-160
- Lone Tree Way
- Hillcrest Ave
- Willow Pass Rd
- Ygnacio Valley Rd
- Contra Costa Blvd
We do this across our service area:
Each link opens that town's heating and air page.
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Read more reviewsColton was great. He found the problem right away and did a temporary fix to get my a/c running until he could get the right part ordered. He also made sure every inside was working well.
Questions we hear
Can I just extend my main house ducts into the ADU or addition?
Sometimes, for a small addition right next to the existing system, but it rarely works for a detached ADU or a garage conversion. The original furnace and ducts were sized for the original house, and long new runs lose air and leave the new room uncomfortable. A separate mini-split or small heat pump keeps the new space independent and lets a tenant or family member control their own temperature.
Is a ductless mini-split the right choice for an ADU?
For most studio and one-bedroom ADUs, yes. A single wall or ceiling cassette head can handle an open floor plan, and a two-zone system covers a separate bedroom. Larger units with several rooms, or owners who don't want visible indoor heads, may be better served by a small ducted heat pump with short duct runs in a soffit or attic. We will lay out both options when it makes sense.
What energy code rules apply to ADU heating and cooling?
A new detached ADU is generally treated as new construction under California's Energy Code, and the 2025 code that took effect January 1, 2026 uses heat pumps as the baseline for space heating. Your designer or energy consultant prepares the compliance documents, and some installs need third-party ECC (formerly HERS) verification before final. We install to the approved plan and coordinate that testing so the HVAC side is ready for inspection.
Will my electrical panel handle an ADU heat pump?
It depends on the panel size and what else the house already runs. A mini-split for a small ADU draws far less than a central air conditioner, but an older 100-amp panel that also feeds an electric range, dryer and EV charger may not have room. We look at the panel early and tell you what the equipment needs, so your electrician can plan any upgrade before the walls are closed up.
Do you work with ADU builders and general contractors?
Yes. We can price the HVAC from architect or designer plans and work to the builder's schedule. We time the rough-in around framing and insulation, coordinate the outdoor unit pad and line set route, and come back for start-up and testing once power is on. Homeowners acting as their own general contractor are welcome too. We just need the plans and a realistic timeline.
Related services
All servicesBlue Star Heating & Air is just a call away!
Send us your ADU plans or describe the space, and we will recommend a system and put a written quote together. Call (925) 584-2428 to get started.