BOLDR HOME

Mini-Split for Detached Garage: Sizing, Wiring and Best Pick

by Dua Jones June 2, 2026

A detached garage presents specific HVAC challenges compared to an attached garage — it has no connection to the home's electrical panel (requiring a sub-panel), is often more exposed on all four sides, may have worse insulation, and the line set must span the distance between structures. This guide covers the complete approach to installing a mini-split in a detached garage, including the sub-panel requirement, sizing for the exposure, and the best models for year-round use.

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How a Detached Garage Installation Differs

Factor	Attached Garage	Detached Garage
Electrical supply	Run circuit from main panel	Sub-panel in garage fed from main house — additional cost
Thermal exposure	One wall shared with house	All four walls exposed — higher heat loss and gain
Line set routing	Through wall directly	Through wall + across yard underground or overhead (code-compliant)
Maximum line set length	Typically 15–50 ft	Can reach 100+ ft if garage is far from house — check model's max

The Sub-Panel Requirement

A detached garage mini-split requires its own dedicated 240V circuit. In a detached structure, this circuit must be fed from a sub-panel installed in the garage, which in turn is fed from the main house panel. Key points:

A licensed electrician must run the underground feed from the main panel to the garage sub-panel — this must meet burial depth requirements (typically 24 inches for rigid conduit, 12–24 inches for underground feeder cable depending on jurisdiction)
Sub-panel installation adds CAD $1,500–$4,000 / USD $1,200–$3,500 to the project cost if one does not already exist
If a sub-panel already exists in the garage, a dedicated mini-split circuit can be added for CAD $400–$800 / USD $300–$700

Sizing for a Detached Garage

Garage Size	Insulation	Recommended BTU
Single car (200–250 sq ft)	Insulated walls + door	12,000–18,000 BTU
Two car (400–500 sq ft)	Insulated walls + door	18,000–24,000 BTU
Two car (400–500 sq ft)	Uninsulated or minimal	24,000–36,000 BTU

Size 20–30% larger than you would for equivalent square footage inside the house — the four-sided exposure in a detached structure increases heat loss and gain significantly compared to an attached garage with a shared house wall.

Line Set Length Considerations

Most residential mini-splits support line set runs of 25–75 feet without refrigerant charge adjustment. For longer runs (75–150 ft), additional refrigerant must be added at installation — a licensed HVAC technician calculates the additional charge based on the extra line set length. Confirm your chosen model's maximum line set length before purchasing — exceeding it requires a commercial-grade system.

Frequently Asked Questions

Can I run a mini-split line set underground between the house and garage?

Yes — underground line set runs are common for detached garages. The refrigerant lines must be properly insulated and enclosed in conduit meeting local burial depth requirements. The installation is more complex and expensive than an above-ground run, but results in a cleaner installation. Your HVAC installer will advise on the best routing option for your specific property layout.