Heating and cooling a garage or workshop with a mini split

Garages were never built to be comfortable. They have an uninsulated concrete slab — a huge thermal mass that soaks up heat all day and radiates it back — a big uninsulated overhead door, thin or no wall insulation, and no ductwork. A closed-up San Antonio garage can climb past 95° by midday.

And here's the part most people don't expect: you legally can't just tie the garage into your home's HVAC. Building code prohibits a garage's air from mixing into the home's air system, because that air can carry car exhaust, fumes, and chemical vapors. So extending central air into the garage isn't just impractical — it's off the table.

A self-contained single-zone mini split is the clean, code-compliant way to condition a garage. It's a sealed system that conditions the garage's own air without exchanging any with the house, so it sidesteps the code issue entirely. And because every unit we install is a heat pump, the same system that cools the shop in July heats it in January — so the space is finally usable year-round.

The install is simple: an indoor head mounted high to handle the open volume, a three-inch hole through the garage wall, and a line set to the outdoor unit.

A garage is a single-zone job — typically $3,000–$5,500 installed, about a day. The catch is sizing: a garage needs more cooling and heating capacity than its square footage suggests, because of the uninsulated door, the slab, and the poor wall insulation. We size up to the real BTU load rather than the floor area. A large multi-bay shop or one full of heat-generating tools climbs from there.

Size for the garage's real load, not its floor plan — an uninsulated door and slab make a garage behave like a much bigger room, and a Manual J accounts for that. If you run a working shop with welders, compressors, or a lot of equipment, tell us; that heat is load we add into the calculation. Weatherstripping and insulating the overhead door pays off fast, letting a smaller unit keep up and cut runtime. This is a space where right-sizing matters more than almost anywhere else.