A journey into the workshop. #60: Air Conditioning a windowless garage workshop.

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Blog entry by dbhost posted 06-11-2010 04:07 PM 4363 reads 0 times favorited 4 comments Add to Favorites Watch
« Part 59: Bummed out by the weather... Part 60 of A journey into the workshop. series Part 61: What little I could do today... »

Okay, The Royal Sovereign 13.5K BTU Unit rolled in on UPS yesterday, and was installed at the hottest point of the day. Installation method is / was. (This WILL change soon as I have trim, and hardi board coming to update things).

Bottom 14” sheet rock removed from post between garage doors. This stuff is saturated from 26 years of humidity, combined with no water seal on the sides of the doors until 6 months ago, removal was just pushing slightly in until the bulk of it crumbled away. Then take drywall saw to cut the remaining good stuff down so it is clean and square.

Measure and mark location for intake / exhaust ports.

Drill starter hole with spade bit.

Jig saw the holes.

clean up holes with rasp. Lower hole in bad shape. Masonite falling apart. (Did I mention siding is one of my projects for this year?). This will be replaced with Hardie siding this weekend.

mount ports in holes with drywall screws.

Attach A/C intake / exhaust hoses.

Plug in A/C and test.

Results? Yesterday was a particularly HOT and HUMID day, and my shop got up to 86 deg F by the doors (where the T-stat on the A/C is). Within 1 hour, temp in shop dropped from 86 deg F to 76 deg F, HUGE difference in humidity as well. LOML noticed this as well.

Things noted that need to be addressed with final project.

#1. Heat gain through siding where port passes through. I need to fully knock out the sheet rock, after the siding pieces are replaced, and insulate the gap. The problem there is that the void is 10” wide. I may just blow in a couple of cans of expanding foam , cut it smooth and put the drywall on top.

#2. Second overhead door completely uninsulated and radiating HUGE amounts of heat into the shop. This has GOT to change NOW. This is part of my upcoming projects.

#3. The heat in here has GOT to accelerate my need for doing my wiring / insulating on the east and west walls of the shop. At that point, the shop should be fully insulated.

What I am happy with in regards to this unit.
A. Quiet operation.
B. Effective cooling.
C. Cost effective.
D. 2 hose unit. FAR more effective than the single hose jobs.

What I dislike about this unit.
A. Relatively weak fan, I had to use a box fan to help distribute air so one area of the shop wasn’t ice cold and the rest burning up.
B. Unit was unable to overcome heat gain next to uninsulated door in direct sun. In all fairness, it would be extremely unreasonable to expect ANY A/C to overcome that much heat gain. I would have to shoot freon directly at the door to cool it off… That is what radiant barrier foam board is for…
C. High amp draw. Okay well not really, but I kind of forgot to take the compressor out of the equation too, and with the air compressor, a box fan and this A/C on a single 20 amp circuit, I threw a breaker. Duh…

After the success of my initial cooling test run on this unit. I have every reason to believe that it is more than sufficient for keeping my little 375 sq/ft garage workshop comfy cool once the insulation is in place.

Now I see a LOT of guys talking about air conditioning their shops, and more than a few are talking about cooling uninsulated shops. Now if you understand WHAT air conditioners really do, the fact that they make air cold is a happy accident. Sort of… They don’t add cool air, they take the heat out of the air present, and move it elsewhere by use of a refridgerant such as freon. which in turn heats the exhaust air (and on this unit in my exhaust vent there is a LOT of heat…). If you are bringing heat energy back into the air space by lack of insulation, or heated air intrusion, no matter how large or efficient your air conditioner is, you will never have good cooling. So my point is INSULATE as well as add an air conditioner so you can get, and keep your cool…

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4 comments so far

View 8iowa's profile


1580 posts in 3784 days

#1 posted 06-11-2010 04:32 PM

Your point about insulation is very appropriate. Unless you wish to add considerably to the rotational velocity of your electric meter, attention to insulating the garage is critical.

Gainesville, FL summers are very hot and humid. Without a reasonable amount of A/C I can literally watch things rust. I put foam insulation between the studs of the 20’ outside wall, and cut 1” thick foam insulation panels and glued them to my metal garage door to insulate it also. Vinyl “seal stop” on the outside of the garage door seals the gaps that would otherwise leak cooled air like a sieve.

Rather than block the only window, I installed a “thru the wall” 12,000 BTU A/C unit on it’s own 15 amp circuit.

-- "Heaven is North of the Bridge"

View dbhost's profile


5723 posts in 3255 days

#2 posted 06-11-2010 04:59 PM

Yeah, Gainesville is similar in climate to Houston Metro, maybe a shave less humid due to it being inland further, but only ever so slight…

Unfortunately, due to HOA covenants & restrictions, and the only available walls being bricked, I didn’t have a through wall unit as an option. And honestly, the split units just cost too stinking much…

On the insulation thing, I got on this kick after I got hit with a $680.00 electric bill this past winter, after my roof got replaced. I looked in my attic to find the gravel bits from the old shingles matting down EVERYTHING, and about 1/4 of my original insulation was MISSING. Oh well, I had always wanted to pack MORE insulation in there. Original was only R19 anyway. I have been rolling in R30 at every opportunity. I turned my attention to the garage first since there was none at all, and R30 was a direct fit. A wonderful thing actually… The temp differential on a dry day is amazing. And there is a HUGE difference when I stand next to the overhead door that is insulated, compared to the one that is yet to be done. You can just FEEL the heat pouring in through the uninsulated door. The air gap between siding and sheet rock offers a tiny bit of an insulating barrier, but not enough to help. There needs to be something there.

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View spaids's profile


699 posts in 3716 days

#3 posted 06-11-2010 06:13 PM

I am very interested in this unit. One thing I have heard about air conditioning a garage shop with a window or portable unit is that it will add a lot of moisture which we all know equals rust. I see that the unit you bought can dehumidify as well as cool. I am curious though. After reading a little in the users manual it appears that it can not dehumidify and cool at the same time. Is this true? How have you been running this unit? Do you run the dehumidifier for a while and then the AC?


PS congratulations on taking your garage shop back from the evil grip of the summer heat. You should see the intense envy in my eyes right now.

PPS how much of a unit do you think I need to get my 550 sq/ft garage down to 75 degrees? I’m in St. Louis. It gets pretty nasty here in the summer. In the low 100’s at the worst of the summer with a heat index 10 to 15 degrees higher.

-- Wipe the blood stains from your blade before coming in.--

View dbhost's profile


5723 posts in 3255 days

#4 posted 06-11-2010 08:49 PM

There is a loaded question if I ever saw one…

According to the MFG, 12K BTU is fine for my 373sq ft shop. I call total Barbara Streisand on that. At least in my environment. My ex father in law lives in our area, and humidity, while high, isn’t as bad as it is here. I would think though, that the issues would be pretty close to the same. Insulate, radiant barrier, seal your air leaks, and THEN think about air conditioning…

Now like I said, my MFG says 14K BTU is fine for 500 sq/ft. Your extra 50 sq ft might bite you in the tail… That is a LOT of space to heat / cool with a single unducted system… Not impossible, but a LOT to do… Mind you, the hoses on this thing that connect it to the vent are only 5’ long… So you will be moving air from one wall, across the shop, and back to cool it all off… Not impossible, but you are going to need a couple of fans to do that…

I am a bit confused on my unit though. Home Depot, and the box BOTH show that this is a 13,500 BTU unit, Royal Sovereign’s web site shows it at 14,000 BTUs. Now reading the owners guide it clearly states the cooling capacity is 13,500 BTU/hr. Somebody goofed on the web site I think…

Anyway, I digress… I do not know of any units on the market that are larger in capacity. 14K BTU is the max I have seen… With your space, the extremity of climate and all, you MIGHT want to consider, if you have room, and it makes sense, a PAIR of 10K BTU units.

On the humidity front. I am completely clueless where you get the impression that air conditioning air, with any true air conditioner would add humidity. Think of a glass full of ice water on a muggy summer day. Where did the water on the outside of the glass come from? No the glass didn’t leak, the water molecules in the air condensed on the glass and went from gas (suspended in the air) to a liquid on the glass. Therefore, the effect of cooling the air with such a system pulled moisture out of the air, not put it in. Air conditioning is the same. Ever seen a car in the summer with a trail of water under the evaporator? That is become water in the air condenses on the cold evaporator, and it collects in a drip pan, and runs out of a tube in the bottom of the car.

Now a portable unit works in the same manner… Of course the water has to go SOMEWHERE right? According to Royal Sovereign, they have some sort of technology that vents the collected moisture out with the hot exhaust air. I am not convinced this is a good idea. I am not convinced it is a bad idea either. But what it IS is moving heat, and moisture from the shop, and out the exhaust vent tube. All in all a good solution.

So a long winded technological discussion answer to your question. Now for the short answer. I am just running it in cool mode because air conditioning the air does dehumidify it…

Sorry, my first career was as an auto mechanic. My specialty was automotive Air conditioning. (IMACA and ASE certified but a VERY long time ago…)

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