Air conditioning for an attached garage

[Jusme]

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

[philip964]

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

Yes insulation that is a given. Walls and attic a must. If the garage door faces East or North maybe later, see if you need it. South or worst West, yeah a real issue. Scavaging off house system with full insulation would be the cheapest. Pushing an ac system is actually better than it loping along running 1/2 the time.

[03Lightningrocks]

I think I would also consider the A/C unit that Syntyr recommended. I would put a turbine type exhaust on the roof and then route the exhaust hose to the roof outside of the bedroom area.

An alternative that might be too expensive in the long run might be to find the duct that provides A/C to the bedroom and install a section that blows into the garage. It would probably be the cheapest (if it can be done) construction wise but the electricity cost on the main A/C unit might be too high. Might even need to get a larger home A/C for that to work.

There is likely not enough air volume to do this. Ducting in residential systems is already set up to the CFM the blower/furnace can provide. I suppose one could install a damper system to shut off the area you don't want cooling and divert it to the garage but with no return in the garage, it won't do a whole lot. Air Conditioning is the act of removing heat. Simply dumping cold air into a hot area won't do much good. The cheapest working option is one of those mini splits. They are precharged and easy to install. They come with line set ready to go and everything you need. One would need an electrical circuit run for it but that is not very expensive.

[RPBrown]

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.

[03Lightningrocks]

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.

Correct again. We have several customers that have mini splits installed. Many of them in uninsulated garden additions(porch conversions) and garage work areas. Sizing it properly is key. I would sugest taking RPBrown up on his offer. It is a pretty easy calculation.

[gtolbert09]

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.

I installed one of those Mr. Cool mini splits in my 2 car garage last year. Garage faces east and once the sun comes up over the house across the street , it can get well over 100 in the garage. The mini split keeps it at 78 all day long. I did insulate the garage door with those pink panels from HD, but the walls are still uninsulated. I’m a big fan of the mini split design.