Quick Answer: A ductless mini-split system (also called a mini-split heat pump) is the best HVAC solution for most room additions and ADUs in San Jose in 2025. A single-zone mini-split costs $3,000-$6,000 installed — it heats AND cools efficiently without requiring ductwork, uses significantly less energy than electric resistance heating or window AC units, and qualifies for the 30% federal tax credit (if it meets the CEE tier requirements). Mini-splits are especially ideal for ADUs and detached additions where running new ductwork from the main house would be expensive or impractical. For a garage conversion ADU or backyard ADU, a single 9,000-18,000 BTU mini-split handles both heating and cooling for the entire unit.
HVAC Options for Room Additions and ADUs — San Jose 2025
Helpful Resources:
| HVAC Option | Cost (Installed) | Best For | Energy Efficiency |
|---|---|---|---|
| Ductless mini-split (heat pump) | $3,000 – $6,000/zone | All additions and ADUs | Excellent (200-300% efficiency) |
| Extend existing central HVAC ducts | $2,000 – $6,000 | Attached additions near existing ducts | Good (depends on existing system) |
| Electric baseboard heat + window AC | $1,000 – $3,000 | Small additions or temporary solution | Poor (100% efficiency heating; poor cooling) |
| Dedicated central air (new system) | $8,000 – $18,000 | Large additions needing multiple zones | Good |
| In-floor radiant heat (electric) | $1,500 – $5,000 | Bathrooms, small areas; not primary source | Moderate |
| Gas wall heater + window AC | $1,500 – $4,000 | Non-ADU small addition | Good heating; poor cooling |
Mini-Split Sizing for ADUs in San Jose
- 300-400 sq ft ADU (studio): 9,000 BTU mini-split (¾ ton) — sufficient for most San Jose climates. Cost: $2,800-$4,500 installed
- 400-600 sq ft ADU (1 bedroom): 9,000-12,000 BTU (¾ to 1 ton) — standard for a 1-BR ADU. Cost: $3,000-$5,500 installed
- 600-800 sq ft ADU (1-2 bedroom): 12,000-18,000 BTU (1 to 1.5 ton) — handles most 2-bedroom ADUs. Cost: $3,500-$6,500 installed
- 800-1,200 sq ft ADU (2-3 bedroom): Multi-zone mini-split with 2 indoor heads — one for living area, one for bedrooms. Cost: $6,000-$10,000 installed
Quartz Construction specifies and installs mini-split HVAC systems for all ADU and room addition projects in San Jose. Learn about ADU construction services. CSLB #1003436 | Call (650) 749-7436.
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