Cooling a bonus room over the garage (the FROG problem)

The finished room over the garage — the FROG — is the single hardest room in most homes to keep comfortable, and it's not close. An interior room is buffered by other conditioned rooms on every side. The bonus room has almost no thermal neighbors:

• The garage below bakes in summer and stays cold in winter — a big uninsulated door, hot cars, and west sun radiate straight up through the floor.
• The attic above superheats and presses down on the ceiling.
• Exterior walls on two or three sides leave it exposed instead of insulated by neighboring rooms.

On top of that, its duct run is usually the longest in the house — added almost as an afterthought, farthest from the air handler — so it gets the least pressure and the least cooling of any room on the system.

A single-zone mini split solves it by not depending on that long, weak duct run at all. The head makes its own cold (or heat) right there in the room, with its own thermostat, sized for the room's real — and unusually high — load. The central system stops trying to over-condition the whole house just to reach one stubborn space.

Install is straightforward: an indoor head on the bonus-room wall, a three-inch hole, and a line set down to the outdoor unit. The routing is often easy here because the line set can frequently run through the garage wall or attic to reach the outdoor unit.

This is a single-zone job — typically $3,000–$5,500 installed, about a day of work. The one wrinkle is that bonus rooms are often large, with vaulted ceilings or knee walls, and they carry a heavier load than their floor area suggests because of the garage below and attic above. That can mean a higher-capacity single head, but it's still single-zone scope unless the space is a full suite.

The room over the garage is the number-one single-zone candidate we see in San Antonio homes. Don't try to fix it by boosting the central system — you'll over-cool the rest of the house chasing one room and never quite win. We size it with a Manual J that specifically counts the exposed garage floor and attic surfaces, because that's where the extra load lives. If your knee walls or floor are poorly insulated, sealing those up lets a smaller, quieter unit carry the room easily — we'll flag the easy wins on the estimate.