Best Air Conditioning Options for Your Garage Conversion or ADU in Southern California
Garage conversions and Accessory Dwelling Units (ADUs) are booming across Southern California - and for good reason. Whether you're creating extra living space, a home office, or a rental unit, a converted garage adds real value to your property.
But there's a challenge every conversion project faces: how do you keep the space comfortable when it wasn't designed to be air conditioned?
This guide covers your best options for cooling a garage conversion or ADU in Southern California's climate, with an honest look at costs, efficiency, and what makes sense for different situations.
This guide covers your best options for cooling a garage conversion or ADU in Southern California's climate, with an honest look at costs, efficiency, and what makes sense for different situations.
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Start With Insulation - Always
Before you think about what type of AC unit to install, make sure the space is properly insulated. A garage that hasn't been insulated for living space will defeat even a well-sized air conditioning system. Heat radiates in through uninsulated walls, ceilings, and especially garage doors - and any cooling you add will simply escape.
Proper insulation for a garage conversion typically means:
Proper insulation for a garage conversion typically means:
- Insulated or replaced garage door (or sealed and insulated if the opening is being filled in)
- Insulated exterior walls (R-13 or better)
- Insulated ceiling/roof deck
- Weatherstripped and sealed windows and doors
Once the envelope is tight, you can right-size your cooling equipment confidently.
Option 1: Extend Your Existing Ductwork
If your home is attached to the garage and your central HVAC system has spare capacity, extending the existing ductwork into the converted space is an option. An experienced HVAC installer would add new ducts and supply/return registers to serve the new room.
Best for: Attached garages where the existing system has sufficient capacity and the duct run is manageable
Best for: Attached garages where the existing system has sufficient capacity and the duct run is manageable
- Pros: Seamless integration with existing system; no separate equipment to maintain
- Cons: Requires professional installation; may overload an undersized system; not usually feasible for detached structures
Option 2: Ductless Mini-Split System (Most Popular Choice)
For most Southern California garage conversions and ADUs, a ductless mini-split is the ideal solution - and for good reason. A mini-split consists of a compact outdoor condenser unit and one or more indoor wall-mounted air handlers. No ductwork required.
Best for: Nearly all garage conversions and detached ADUs
Best for: Nearly all garage conversions and detached ADUs
- Pros: Highly efficient (SEER ratings of 20+ are common); no ductwork; zone control; eligible for manufacturer's rebates; quiet operation; provides both heating and cooling
- Cons: Higher upfront cost than window units
Option 3: Window Air Conditioner
A window AC unit is the lowest-cost cooling option for a small converted space - but it comes with real limitations that Southern California homeowners should understand.
Best for: Very small spaces (under 300 sq ft) where budget is the primary concern
Best for: Very small spaces (under 300 sq ft) where budget is the primary concern
- Pros: Inexpensive; widely available; easy to install in an existing window opening
- Cons: Energy inefficient; creates a security vulnerability; not permitted under California's Title 24 energy code for new ADU construction in many jurisdictions; doesn't provide heating
Note: California's Title 24 Building Energy Efficiency Standards has specific requirements for ADU HVAC systems. Window units may not meet compliance requirements for permitted conversions. Always check with your local building department before selecting equipment.
Cost Comparison
| Cooling Option | Typical Cost | Best For |
|---|---|---|
| Extend Existing Ductwork | See original cost table | Attached garages with available HVAC capacity |
| Ductless Mini-Split System | See original cost table | Most garage conversions and ADUs |
| Window Air Conditioner | See original cost table | Small spaces with limited budgets |
Costs are estimates for the Southern California area and vary based on specific conditions.
For help selecting and sizing the right system for your garage conversion or ADU, call Burgeson's at (909) 792-2222. We serve Redlands, Riverside, San Bernardino, and surrounding communities and can provide a free estimate.
For help selecting and sizing the right system for your garage conversion or ADU, call Burgeson's at (909) 792-2222. We serve Redlands, Riverside, San Bernardino, and surrounding communities and can provide a free estimate.
Frequently Asked Questions
Do I need a permit to add AC to my garage conversion?
Yes, in virtually all California jurisdictions. Adding HVAC to a converted space typically requires a building permit and must comply with Title 24 energy standards. Burgeson's can provide equipment documentation to support your permit application.
What size mini-split do I need for a converted garage?
Sizing depends on the square footage, insulation quality, ceiling height, and sun exposure of the space. A load calculation by a licensed contractor is always recommended.
Can a mini-split also heat my garage conversion?
Yes - modern mini-split heat pumps provide both cooling and heating, making them a year-round comfort solution. This is one of the main advantages over window AC units.
Contact Burgeson's
For help selecting and sizing the right system for your garage conversion or ADU, call Burgeson's at (909) 792-2222.
