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RPBrown wrote: ↑Tue May 25, 2021 7:45 am

Jusme wrote: ↑Mon May 24, 2021 8:27 pm The best option will not be cheap. A mini split system, or any portable unit, will not be sufficient to cool an un-insulated, three car garage. Which is at a minimum 10,000 cubic feet. With three sheet metal garage doors that absorb heat, and allow huge amounts of air, to bypass them. A small unit, will not be much better than fans, and cost more in electricity.
You will need to insulate the exterior walls, and as much of the attic as possible, replace the garage doors with insulated doors, or use some type of adhesive insulation on them. Seal the doors, to reduce the air flow. Either increase the size of your existing HVAC unit, or install a separate dedicated 3 ton unit, for your garage. Install duct work, with return air. This will exchange the air much more efficiently, and you can install a thermostat, which will allow you to shut it off when not in use. Again, this won’t be cheap, but I believe you will be disappointed trying the less expensive options. JMHO

I have to disagree with you on the mini-splits. True, a portable unit would probably not keep up or last very long. A mini-split however can be sized to meet the needs. I have a 20x12 all glass "room with a view" as they were called. 100% single pane glass slightly tinted. Sadly, this was one of the reasons we bought the house in Feb of 91. It had a window unit in it at the time so I didn't think much about it. After several summers (2002) of not being able to enjoy that room, I replaced the window unit with a 2.5 ton mini-split heat pump. The worst it has been since was on the days over 107-110, it would get up to 80.
BTW, when I installed mine, the efficiency of them was 17 SEER. Now you can get them upwards of 20+ SEER. As for price, it depends on sizing. I would have a load calculation performed to make sure it is sized correctly for your situation though. PM me and I can help with that.