A/C in a two car garage

[John Hicks]

An recommendations for a good ac unit? 115 volt would be best. It gets darn hot here (shasta county ca) and by 9 am, it's too hot in the garage to even stay in there. I'm not sure what would be the most efficient without spending more than 600 dollars. The garage is 450 square feet with a 9 foot ceiling. minimal insulation.

 

[Allen Mattsen]

If your HVAC unit is in the garage and you have central air / AC in your house you could consider what I've done and that is to cut out a piece and install a vent, then the same cold air blowing through your house will also have a port to the garage. Cost: about $15.

 

[Mike Johnson]

A swamp cooler is another option if you have a readily available water source. A smaller room would be cheaper and easier to cool, you would want to insulate the walls and ceiling to make any air conditioning system work efficiently. An 18,000 BTU window a/c unit could cool the garage if you insulated the walls and ceiling, and insulated garage doors would help greatly.

 

[Allen Mattsen]

Even an HVAC vent like mine would be fairly miserable without my garage doors insulated, which I did a couple months ago. The walls and ceiling are finished in my 2-car garage shop as well. Ideally, I'd have a mini-split but those can be cost prohibitive. Still, my shop is upwards of 10° cooler than outdoors at present. 77° by my lathe now, so that's acceptable to me. What would improve things is to insulate the ceiling much better than is currently up there.

 

[Dean Center]

Insulation alone can make a big difference. I have 6" insulated walls in my garage shop and the temp stays tolerable on the hottest days. Here that's 90+ degrees, which is quite a bit lower than what you'll encounter in NoCal this year, but the point still holds. Ground temp is cool year round, so try to keep that cool air from getting heated up. When you add an AC, you'll get lots more bang for the buck with insulation, too.

 

[John King]

"Swamp cooler" will only work in ultra low humidity environment. Water evaporation is required to cool the air. High humidity air passing through the "swamp cooler" will not sufficiently evaporate the water to cool the air. - John

 

[Doug Freeman]

I use a window ac unit in my garage, 672 ft2, in MO with hi temp and humidity. I think its 12kbtu, the largest 120v I could find. I keep the temp pretty constant 24/7, so it doesnt have to pull the temp down. Can keep about a 20-22 deg difference from outside. I have an insulated door, walls, and thick insulation in the cceiling.

 

[Keith Mombourquette]

If your HVAC unit is in the garage and you have central air / AC in your house you could consider what I've done and that is to cut out a piece and install a vent, then the same cold air blowing through your house will also have a port to the garage. Cost: about $15.

This is fine as long as the garage will never be used for a car or other internal combustion engine. You have created a path for carbon monoxide to enter the house.

 

[Allen Mattsen]

That's a very good point to make. No vehicles enter the garage. Nor could one fit!

 

[Mark Jundanian]

That's a very good point to make. No vehicles enter the garage. Nor could one fit!

Consider closing off that vent hen you sell the home. The next owner may have different ideas about the proper use of a garage .

 

[Randy Anderson]

Not sure if you've looked at the small portable AC units designed for small apartments or bedrooms. Self contained and vent to the outside via a 5" hose. I tried one and ended up giving it away. My shop is about the same size as yours, insulated garage doors and ceiling but with the neg pressure the unit creates on the room plus my dust collection system running it just couldn't keep up. I could get it comfortable after a long time of running the unit and then suck all of the cold air out in just a few minutes with the dust system. Looking at a mini split now. Would have gone with a window unit but my wife is strongly opposed to me cutting a hole in the brick wall. I don't have any windows to use.

 

[robo hippy]

I would first concentrate on insulation. That is a must if you plan on using your shop a lot in the hot months. Putting up shades on the outside of any windows that get direct sun prevents the sun heat from getting through the windows, same with garage doors, and this holds true even if they are double or triple pane windows and insulated doors. A swamp cooler would work down there around Shasta since it is pretty dry during the summer. They do provide a little relief. Other than that, a small window mount or a ductless set up would help also. Not sure what night time temps are down there. Where I am, it gets down to mid 50's at night so I can open up the windows, with a couple of fans, and inside temps are low to mid 60's in the morning and low 70s by night time.

robo hippy

 

[John King]

Not sure if you've looked at the small portable AC units designed for small apartments or bedrooms. Self contained and vent to the outside via a 5" hose. I tried one and ended up giving it away. My shop is about the same size as yours, insulated garage doors and ceiling but with the neg pressure the unit creates on the room plus my dust collection system running it just couldn't keep up. I could get it comfortable after a long time of running the unit and then suck all of the cold air out in just a few minutes with the dust system. Looking at a mini split now. Would have gone with a window unit but my wife is strongly opposed to me cutting a hole in the brick wall. I don't have any windows to use.

Mini-split is the way go go. They are ultra efficient. My 18,000 BTU mini-split has SEER of 19.2. Installed cost was reduced by energy tax credit. Comfortably cools and heats my 1000 sq ft shop/garage. Ceiling insulated. Foam core garage doors. Walls not insulated. Located in high temp, high humidity area north of Houston, TX. - John

 

[John Hicks]

Some really good ideas! I'm glad I didn't buy a portable cooler. I think I have decided on either a window unit, or a through the wall model. I still have to insulate the door.

 

[Bill Boehme]

Even an HVAC vent like mine would be fairly miserable without my garage doors insulated, which I did a couple months ago. The walls and ceiling are finished in my 2-car garage shop as well. Ideally, I'd have a mini-split but those can be cost prohibitive. Still, my shop is upwards of 10° cooler than outdoors at present. 77° by my lathe now, so that's acceptable to me. What would improve things is to insulate the ceiling much better than is currently up there.

Does your garage also have a return air duct?

If NO, that means expensive cool air is being forced to the great outdoors through gaps around the overhead door, baseboard cracks, windows, any door leading outdoors, and into the attic through pull-down stairs, and ceiling light fixtures. This also means that outside air is being drawn into the rest of the house to make up for the air lost in the garage. Even though the state of Washington could use some cool air from what I hear, it's still not a good way to spend your money.

If YES, you will be dumping a lot of dusty air (especially if sanding, but even from turning dry wood) into the rest of your house. A filter on the garage return air would help, but even the high dollar filters don't catch all of the dust. Not very good for domestic tranquility.

I like the suggestions of using a window air conditioner in the garage. I have a well insulated three-bay garage and cool it with a 24,000 BTU window air conditioner. You could probably get by with a smaller unit, maybe 18,000 BTU.

 

[Randy Anderson]

After trying to get a DIY mini split here before summer ends and a quote for having a local AC company install one my wife relented and I put a 12,000 BTU window unit in this week. My original choice but took a while for her to agree as long as I did it neatly, framed around the hole I cut in the wall and put it where it won’t be seen. Back side of my shop facing the wooded part of the yard. All done as requested. I’m the only person that will ever see it. Working great so far. Much less than a mini split and easy to install.

 

[John Hicks]

After seeing what everyone is doing; I think I'll go with a through the wall ac unit. I have those windows that slide horizontally and don't work to well with a window unit. Since PG&E is our electric supplier, I'd better get a loan for cooling the shop!

 

[Randy Anderson]

John, my window unit has been working great since I put it in last week. My shop is 360 sq ft with attic insulation but no wall insulation. Just OSB on the inside and brick exterior. I went with a 12,000 BTU unit which is at the top end of the range for my shop size but with no wall insulation and a dust collection system that vents to the outside I can suck a lot of cold air out quickly. So far it keeps up and recovers quickly. I can tell it gets slightly warmer when the dust collector is running for an extended period but not an issue since the AC recovers very quickly. I have two overhead air cleaners that run all the time so not sure how the AC air filter will do re dust. Will just check it often.

 

[John Hicks]

I do need to look in the attic and see if it's insulated. I'm hoping it is.

 

[Mark Jundanian]

You're going to have to check your circuits, too. AC will draw a lot of amps and probably will not work and play well with other power tools on the same circuit.

 

[John Hicks]

You're going to have to check your circuits, too. AC will draw a lot of amps and probably will not work and play well with other power tools on the same circuit.

I have to install a 100 amp sub panel with circuits that I'm going to run in conduit on the walls. There is a couple 20 amp 110 receptacles already in the garage, but that's it.

 

[Lou Jacobs]

Sounds like your decision is made, but I’m going to register a vote in support of John King’s suggestion:

Mini-split is the way go go. They are ultra efficient.

I installed a Mr. Cool (with precharged lines so homeowner can do it) mini-split last august. While it is more expensive than a window a/c initially, it is very efficient to run. I’ve barely noticed a change in our electric bill, and it’s allowed me to turn on some very hot days would have been unbearable without. Added benefit is that it also creates heat in the winter, again, letting me use the shop when I’d otherwise be too cold. It’s a neat system. We just doubled down and installed (pro installation) two units supplying three bedrooms and entire downstairs in our house. It’s been a godsend during the past six weeks. Gave away our window units.

 

[Mike Goetzke]

Years ago I purchased a large window unit off CL in the fall for $75 for my attached 2-1/2 car garage. It's 12K or 15K BTU's but still ran off 120V. I'm in the Chicago area and it's unbelievable how it cools down so fast and cuts the humidity.

 

[Mark Jundanian]

Years ago when I had my shop wired I made all the circuits (except the lights) 20 amp, instead of 15. I also put in quad receptacles with each outlet pair on a different circuit. This has worked out well as I can spread out the loads. Wish I'd put in more outlets, though.

 

[Leonard Niemi]

Mini-split is the way go go. They are ultra efficient. My 18,000 BTU mini-split has SEER of 19.2. Installed cost was reduced by energy tax credit. Comfortably cools and heats my 1000 sq ft shop/garage. Ceiling insulated. Foam core garage doors. Walls not insulated. Located in high temp, high humidity area north of Houston, TX. - John

How have you handled dust getting into your mini split ? I considering one myself.

 

[GRJensen]

How have you handled dust getting into your mini split ? I considering one myself.

About once a month, I pull the two filters on my mini-split and vacuum them out. Five years and counting with no problems.

 

[Mike Johnson]

When building a shop from scratch one of the best systems for year around comfort is a thermal loop system in or under the concrete slab. In the winter months warm fluid is circulated through the loops and heat radiates upward into the work space. the concrete slab is your thermal mass which regulates the temperature in the work space very evenly throughout the entire area of the building. During the summer months you can switch over to a chiller system that cools the fluid that circulates through the loop systems, this will also do a very good job throughout the shop area maintaining an evenly regulated temperature in your shop area. With these systems you don't have the dust and filter issues to worry about compared to forced air systems. One client I worked with had a similar system with a water heater hooked up to the loop and a wind turbine generator outside that generated power to heat the elements in the water heater and a small B&G pump to circulate the water through the loops in the floor. The concrete floor was basically the thermal mass storage for the system. In the summer months he would switch over the loops to a cold water supply coming from a well that used the cold water to chill the loops in the concrete and the water was then used for farm animals and irrigation needs. Very low cost system to heat and cool a work space and office area.

 

[John King]

How have you handled dust getting into your mini split ? I considering one myself.

Leonard - My filters are ultra fine mesh screen. I pull them out every four weeks and gently wash, dry and re-install. May clean more frequently if doing some very dusty work. - John

PS - I have a Jet air filtration unit mounted on the ceiling above my lathe and use a dust extraction system when sanding on the lathe; therefore, very little airborne dust to be captured by the air conditioner filters. - J

 

[John Hicks]

"Swamp cooler" will only work in ultra low humidity environment. Water evaporation is required to cool the air. High humidity air passing through the "swamp cooler" will not sufficiently evaporate the water to cool the air. - John

It is very dry here (average humidity is around 25 percent) We have a big roof mounted swamp cooler in the house and the inside humidity never goes over 40 percent......unless it rains.