Quick Answer: The best way to heat a garage or ADU in the Bay Area in 2025 is a mini-split heat pump system (also called a ductless mini-split). It heats AND cools, uses electricity (no gas required — compatible with solar), is required by California’s Title 24 energy code for new ADU construction, and is 200-300% efficient at heating compared to electric resistance. A 12,000-18,000 BTU mini-split for a 400-700 sq ft ADU costs $3,500-$8,000 installed. For an uninsulated garage being used as a workshop (not a conditioned living space), a propane or natural gas unit heater ($800-$2,500 installed) is the fastest and cheapest option — but cannot be used in a permitted living space.
Heating Options for Garages and ADUs in the Bay Area 2025
Helpful Resources:
| System | Cost Installed | Heats & Cools? | Permit Required? | Best For |
|---|---|---|---|---|
| Mini-split heat pump (ductless) | $3,500 – $8,000 | Yes — both | Yes (electrical + mechanical) | All ADUs; conditioned garages; California code compliant |
| Through-wall heat pump (PTAC) | $1,500 – $4,000 | Yes — both | Yes | Small ADUs and garage conversions; hotel-room style |
| Electric wall heater (baseboard/panel) | $500 – $1,500 | Heat only | Usually not (under 240V threshold varies) | Small areas needing supplemental heat; low first cost |
| Gas or propane unit heater (overhead) | $800 – $2,500 | Heat only | Yes (gas permit + mechanical) | Unfinished garages and workshops only — NOT for living spaces |
| Infrared radiant heater (electric) | $400 – $1,500 | Heat only (radiant) | Usually not | Workshop or open garage where heat loss is high |
Why California Requires Mini-Splits for New ADU Construction
California’s Title 24 Energy Code (updated 2022 and 2025 versions) requires that all new ADU construction meeting the requirements for a “dwelling unit” include a heating system capable of maintaining 70°F throughout the conditioned space. Gas furnaces in new construction are increasingly prohibited under reach codes in many Bay Area cities (San Jose adopted a natural gas ban for new construction in 2021). Mini-split heat pumps satisfy both the heating requirement and the California Clean Energy reach code because they run on electricity only.
Quartz Construction installs mini-split systems in all ADU projects throughout San Jose. Learn about ADU construction. CSLB #1003436 | Call (650) 749-7436.
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