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Portable AC for Garage Workspace

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Forum topic by Chas7715 posted 06-20-2016 05:02 PM 1127 views 1 time favorited 37 replies Add to Favorites Watch
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Chas7715

23 posts in 351 days


06-20-2016 05:02 PM

Hi All,

My workspace (I can’t really call it a shop) is one side of a three car garage. Here in OK we are sweltering with 95+ degree temps with over 85% humidity. Even in the mornings the garage is hot so doing any work out there is almost impossible. I tried it and I just sweated all over my tools. By the way, sweat is terrible for cast iron.

I have been contemplating buying a 10,000 BTU portable AC unit for this space. Has anyone used a portable unit? If you have, any feedback? Is this just a stupid idea? Please don’t suggest a mini-split. No going to happen right now.

Help me out folks.

Chuck

-- Perfection is highly overrated!


37 replies so far

View clin's profile

clin

514 posts in 461 days


#1 posted 06-20-2016 05:39 PM

I have not used one of those, and do like my mini-split (just had to say it). Those portable AC units still need to be vented to the outside. They draw in outside air to move across the condenser and then back outside again. A window is typically used. If you had a window, a more typical window AC unit may be less expensive.

As for the size, who knows?

It sounds like you would actually be cooling the whole 3-car garage (1000 sq ft or so). That’s quite a bit for a sub 1-Ton AC unit in a probably not well sealed space.

More importantly, is the garage insulated? If not, I don’t think it would do the job. First and foremost, insulate and seal.

If your garage doors are not insulated, insulate them. You can glue on foam board. Just don’t over do it and add too much weight to the door.

Does the garage have a ceiling, or is it exposed rafters and you can see the roof sheathing?

If no ceiling, add one and insulate it. Or at least staple some of that silver sided bubble wrap type radiate barrier to the rafters. Silver side towards the roof. That would at least be a radiate barrier, minimal insulation, and a significant airflow seal.

And, perhaps you can add some plastic sheeting or other to divide the shop space from the rest of the garage. Just cool that side. It won’t be as good as a full blown wall divider, but anything that keeps the cool air from easily flowing around the whole garage would help.

-- Clin

View Richard H's profile

Richard H

489 posts in 1145 days


#2 posted 06-20-2016 05:45 PM

I have a portable AC unit that I use in the garage and I am not that happy with it. It just doesn’t put out the volume of air needed to keep the room cool and more importantly the humidity down for my 20X20 garage space. My garage is not horribly hot as it has a insulated garage door and brick siding with trees around it but even than the unit I have I wouldn’t recommend for that space. A window unit would probably work a lot better especially if you can do 220Volts.

The one I have is a 14,000 BTU LG unit I bought at Home Depot a few years ago for a rental house we lived in without AC that I repurposed when we moved.

View joey502's profile

joey502

487 posts in 983 days


#3 posted 06-20-2016 07:27 PM

I use a window unit and dehumidifier in my 24×24 garage. My walls, ceiling and foor are all insulated. The unit is a Frigidaire 12,000 btu unit from lowes. My set up will keep the shop at 70 when the temp outside is in the mid 90’s and humity is 70%.

10,000 btu is not enough for that size space even if the garage is insulated. I think you will be very disappointed with it’s performance.

The window unit would be better, the dust on the floor level is worse than that floating at window height. Buy a couplr if the cut to fit filters to help keep your unit clean and operating efficiently.

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Chas7715

23 posts in 351 days


#4 posted 06-20-2016 07:59 PM

Thanks for the replies!

Situation:
No windows. Brick veneer, 2 exterior walls, insulated garage doors, back wall shared with insulated living space, rocked ceiling with no insulation in attic space. And no insulation in the two exterior walls (rocked as well).

So no window AC, which would have been done by now if I had a window.

Opinions seems to lead me to believe I should save my money and not buy a portable unit. And maybe insulate the garage space better in the interim.

-- Perfection is highly overrated!

View dbhost's profile

dbhost

5607 posts in 2697 days


#5 posted 06-20-2016 08:08 PM

I have had a portable unit for about 6 years now, ducted using 5” dryer vents through the wall segment between the garage doors. It is already failing, and dual hose units are hard to come by these days.

I am assuming you are in a windowless garage as I am. IF I were to do it over again, I would… And I am ALSO assuming that you can divide off your workspace from the rest of the garage. Get creative, lots of us do!

#1. Start with at LEAST 12K BTU. My Garage / Workshop is 18×20 which is really more like a 1.5 car, or 2 1980s Toyota Corolla garage size, with 8’ 6” ceiling height, #2. Use a Window unit instead of a portable unit. The portables are extremely trouble prone. #3. Build a manifold box, with a small squirrel cage blower to move air across the coils and in / out of the box. #4. Mount the box / AC high up. Hot air rises, cold air sinks, cook the upper air first and it cascades down. #5. Make sure you have a means to get the condensate (water that comes OFF of the air conditioner) out of the box without it touching the wood.

According to typical sizing charts, and let’s assume you are in a space about like mine, and don’t have the benefit of insulation like I went through the trouble and expense of installing, you will want a 12K BTU + 50% for efficiency loss due to no insulation, or 18K BTU portable unit. I know of none on the consumer market. That would mean your next option in portables would be 2 10K units that would suck up TONS of energy and be horrifyingly expensive to buy, maintain, and operate.

Window units have a higher operational efficiency and as such tend to need a lower rated unit for the same space, 10K BTU for each 20×20 space insulated, + 50% for non insulated, so 15K BTU.

At that point, you are looking at a 220v power requirement to operate.

If you haven’t figured it out yet, I am trying to lead you toward the idea, insulation / radiant barrier is your friend in a hot climate. IF you can pony up the bucks to do a proper insulation job, do it! And then go through the steps above, separate your workspace insulated and dust separated as much as you can, and then go with a 10K BTU window unit in a box…

IF you have an actual window you can use, all the better!

Joey 502 is right, and I should mention, a LOT of it depends on actual dimensions. My shop space is 360sq ft with an 8.5 ft ceiling height giving me 3060 cubic feet to keep cool. His shop being 24×24 and I have to assume a 9ft ceiling as that is the standard, mine is short, is 576 sq ft, or 5184 cubic feet.

For what it’s worth. My portable unit that is sick (Bad bearing I think) is a 12.5K BTU unit it struggles, a LOT to get the shop, insulated and sealed as it is, to 74 degrees when it is in the upper 90s / 90% humidity.

If I can’t fix this unit, I WILL be doing what I said above, and build the cooling box for a window unit as my garage has no windows, and even if, the HOA would have a screaming conniption fit if I hung a Window unit out where it could be seen!

-- My workshop blog can be found at http://daves-workshop.blogspot.com

View clin's profile

clin

514 posts in 461 days


#6 posted 06-20-2016 09:15 PM

Insulate first. Keep in mind that with good insulation, even if you don’t add AC, the space won’t get as hot. Insulation evens out the temperature swings in a space. Of course, insulation isn’t going to make it comfortable to work, just less miserable. But it will obviously give any added AC a fighting chance.

Also, when it comes to AC and humidity, bigger is NOT better. The longer the AC unit runs, the more humidity it will remove from the air. This is a common mistake when sizing AC for homes. Contractors tend to error on the high side (like 2 to 3X high). So you get a space that chills fast, but never dries out.

For a reference, I have converted a 3rd garage bay (12’x24’) for my shop. I walled it off form the rest of the garage with a fully insulated 6” (R19) wall. Ceiling already had R30. Two other walls common to interior and converted the garage door to a double door with R13 insulation.

Low humidity where I live, but 105 F yesterday, and my 7,000 BTU/Hr mini-split just cruises.

Also, when looking at AC ratings, the BTU rating will be at one specific condition of outside temperature, set temperature, and humidity. So if possible get data on whatever you use and check what its performance is at your expected conditions.

-- Clin

View ThistleDown's profile

ThistleDown

12 posts in 182 days


#7 posted 06-20-2016 09:22 PM

I had one of those units in my switch room when I had my telephone business. It ran ALL the time and had to be vented outside, had to have condensation removed and was noisy as h-double-hockey sticks. Now you may think the noise is no issue in the shop but, we do not saw, drill, route, plane… the Whole time like this thing ran.

When I built my shop 2 years ago I got this, both heat and cool, and you can’t beat the price. Could not be happier.
https://www.amazon.com/Koldfront-Heat-Cool-Window-Conditioner/dp/B00QXSC3V2/ref=cm_cr_othr_d_product_top?ie=UTF8

You can punch a hole in the wall like I did, otherwise this will go in a window. They also have smaller units, this one does fine in my 616sqf shop.

-- My biggest fear is that when I am gone, my wife will sell my tools for what I told her I paid for them.

View JeffP's profile

JeffP

573 posts in 856 days


#8 posted 06-21-2016 12:15 PM

Maybe try to come up with a way to move well-filtered air between the main house and the garage?

Obviously there is a dust problem that has to be solved, but as far as base cost and cost of “installing it”, seems like this will likely be the cheapest way to get the garage cooled down some.

Kind of depends on how much spare capacity the house system has too. Also maybe your house would rise in temp some, if it can’t keep up.

Just a wild-assed idea to consider.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View Fred Hargis's profile

Fred Hargis

3942 posts in 1958 days


#9 posted 06-21-2016 02:53 PM

I had just given my portable unit to the Habitat restore. I had windows in my shop, but they were very small and the largest window AC I could fit in there was 8K BTU. Add to that the fact both windows were exposed to direct sunlight most of the day. I thought the portable unit was just the ticket. I could get a larger one (12K BTU), it would work with the smaller window opening, and not be in the sun. Boy, was that a mistake. The 12K portable didn’t cool as well as the 8K window unit it replaced. I’m only guessing, but the portable unit discharged a huge amount of air out the window, and the makeup air leaking in was the hot outdoor stuff. So it not only didn’t cool, but it also didn’t dehumidify. I used it most of last summer, and this spring gave it away. Tjis wasn’t a cheap unit either. A Honeywell, and cost about twice what the window unit cost. Even so, if that’s all you can use the decision is made. Just be sure to upsize it a good deal from what you think a window unit might be.

-- Our village hasn't lost it's idiot, he was elected to congress.

View onoitsmatt's profile

onoitsmatt

227 posts in 641 days


#10 posted 06-21-2016 03:18 PM

I’ve been pondering the same issue for a couple of summers now here in Arizona. Same situation, no windows, brick construction. My latest wild idea is to fully enclose the third garage bay (mine has a wall partially separating it from the 2-garage bay). But where the overhead door is, build a wall a foot or so inside and mount a window unit in that wall. When in use, open the overhead door to let the hot air and condensate out. The issue is how to build a wall there that allows the overhead door to open.

Ducting inside a/c in garage is a code violation. You can’t have car exhaust etc freely going in your house. Plus firewall is required between garage and living area.

-- Matt - Phoenix, AZ

View Rentvent's profile

Rentvent

148 posts in 314 days


#11 posted 06-21-2016 05:54 PM



Thanks for the replies!

Situation:
No windows. Brick veneer, 2 exterior walls, insulated garage doors, back wall shared with insulated living space, rocked ceiling with no insulation in attic space. And no insulation in the two exterior walls (rocked as well).

So no window AC, which would have been done by now if I had a window.

Opinions seems to lead me to believe I should save my money and not buy a portable unit. And maybe insulate the garage space better in the interim.

- Chas7715

Unless you can get the laws of thermodynamics changed, any type of active cooling will require penetrating a wall or ceiling to vent the heat. The advantage of the split or ductless system is that the penetration is only one or two 1” holes.

View Chas7715's profile

Chas7715

23 posts in 351 days


#12 posted 06-21-2016 06:41 PM

Thanks for all the replies/suggestions/general help!!!!
This is why this forum is the best!!

I have an A/C company coming on Friday for a quote on a mini split. We’ll see if I survive the shock! And I think I jinxed myself with all this talk about A/C as I had to layout $400 last night because my house A/C crapped out.

As for insulating, all of the garage walls and ceiling are sheet rocked. I can blow in some insulation in the ceiling. Should I tear off the sheet rock on the walls to insulate with blankets or attempt to blow in insulation in the studs cavities? If so, is that a DIY job?

DBhost: can you provide more details concerning a manifold box and a window unit??

Thanks all,

Chuck

-- Perfection is highly overrated!

View clin's profile

clin

514 posts in 461 days


#13 posted 06-21-2016 09:12 PM



Thanks for all the replies/suggestions/general help!!!!
This is why this forum is the best!!

I have an A/C company coming on Friday for a quote on a mini split. We ll see if I survive the shock! And I think I jinxed myself with all this talk about A/C as I had to layout $400 last night because my house A/C crapped out.

As for insulating, all of the garage walls and ceiling are sheet rocked. I can blow in some insulation in the ceiling. Should I tear off the sheet rock on the walls to insulate with blankets or attempt to blow in insulation in the studs cavities? If so, is that a DIY job?

DBhost: can you provide more details concerning a manifold box and a window unit??

Thanks all,

Chuck

- Chas7715

Mini-split is going to be some thousands of $$$, but you’ll know soon enough. I’d get more than one quote. I had a system put in last August (one outdoor unit feeding three indoor units, one in my converted garage shop space). It was a bit over $7k. That’s of course more than you would be doing. But I had quotes of $20 K.

Also, even the guys I went with initially quoted my much larger units than I needed. That’s why I did my own Manual J calculation. In the end, had them put in three of the smallest Fujitsu units possible (7,000 BTU/hr). We’ve recently had as hot a weather as we get, and as expected, they have handled it just fine.

If you don’t run a Manual J calculation, sizing the system is just guessing, no matter what they say. There are too many variables. Doesn’t matter what your neighbors house needed. Unless the situation is identical, what works for one won’t necessarily work for the other.

If you don’t run a Manual J calculation, you will almost certainly oversize it.

You don’t want to over size any AC system, but you really don’t want to do it with mini-splits. Sized properly, they can be very efficient. Oversized, and they aren’t going to be much better than a common full on/full off AC unit.

Plus, if oversized, they won’t dehumidify well.

Keep in mind mini-splits are really meant for continually cooling a space. If what you have in mind is just cooling things down for a Saturday afternoon and leaving it hot the rest of the week, I’d cut a hole in the wall and just stick in a powerful window unit. Do it right so you can convert the hole to a Window so the house won’t look weird when you go to sell it.

As for insulating. If the wall cavity is a full 2×4 sized space, I’d consider blowing in insulation. But make sure it is appropriate for your area. You can create moisture issues without a vapor barrier.

But it’s not the worst idea to pull off the sheet rock, insulate with batts, then replace the wall board with plywood. Not of course the wall common to the inside of the house, that needs to remain a fire wall with appropriately thick sheet rock.

Are you think of cooling the whole garage? Or are you going to partition it somehow. That will make a huge difference on what size AC system you need.

-- Clin

View ki7hy's profile

ki7hy

493 posts in 204 days


#14 posted 06-22-2016 03:39 PM



I ve been pondering the same issue for a couple of summers now here in Arizona. Same situation, no windows, brick construction. My latest wild idea is to fully enclose the third garage bay (mine has a wall partially separating it from the 2-garage bay). But where the overhead door is, build a wall a foot or so inside and mount a window unit in that wall. When in use, open the overhead door to let the hot air and condensate out. The issue is how to build a wall there that allows the overhead door to open.

Ducting inside a/c in garage is a code violation. You can t have car exhaust etc freely going in your house. Plus firewall is required between garage and living area.

- onoitsmatt

Matt, I don’t recommend going through the cost or trouble in AZ. I have put a ton of research into this and in our climate (low humidity) it’s really not worth the expense of the full on AC unit and all of the work. Your situation might be similar but I have a side door on my garage I crack open about 10” and I have a portable swamp cooler I use in front of that door. I crack the garage door about 3 inches to let the air move through.

I’m not saying it was like sitting in my living room this last weekend but it was extremely tolerable. Especially with temps hitting 120 degrees on Saturday. With low humidity an evap cooler is perfectly fine and a lot less hassle overall. I picked a Honeywell up at Lowes for about $400 and the wife found a coupon for 10% off total purchase.

The original poster has the real issue. Heat sucks but humidity + heat really sucks.

View onoitsmatt's profile

onoitsmatt

227 posts in 641 days


#15 posted 06-22-2016 04:01 PM

Thanks for the input Ki7hy. I’ve got a big portable mastercool that i bought last year. I haven’t used it in the shop yet. I’m primarily a hand tool shop and am concerned about the rust. Also added humidity to the shop and its affect on dry wood. Have you had any trouble with either of these with your evap?

-- Matt - Phoenix, AZ

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