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Forum topic by a1Jim posted 06-05-2016 03:54 PM 2042 views 1 time favorited 61 replies Add to Favorites Watch
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118142 posts in 4456 days

06-05-2016 03:54 PM

Topic tags/keywords: question

Hi Friends
Living in southern Oregon we have pretty mild weather but of late our summers and now late spring we have had some pretty hot days(for our area)a hundred degrees. this has brought me to the point that I’m considering putting AC in my shop. I’ve gone online and have done a little homework but I’m still confused as to what to found some pretty reasonably priced split unit AC’s online that have good reviews from $1000-$1200 with all the items needed to install it.
I’m a 30 year contractor so it does not seem too scary installing a unit like that,but as a contractor, I also know it’s not what you know that hurts you it’s what you don’t know that bites you in the rear,so this is why I’m seeking some AC pros advice out there. In my research, I find these kinds of units cool and heat,I already have good gas heat in my shop. My questions involve: what brands are best ? Is these type of unit good for a shop environment ? Is it possible to install this type of unit myself ? What size to get ( my shop is about 28×30 with 14’ high ceilings with a guest apartment built above),the largest units in my price range seem to max out at 2200 BTU units and some online calculators put my shops needs at close to 48.000 BTU’s ,if i go smaller than my needs will it still take longer to cool or just not cool at all ? What about one or more wall units instead ?

Here’sone unit I’m looking at.

Some details
Max budget $1400
I have 12 dual glaze windows 12”x2’ at the top of my ceilings and one 10’x10’ insulated shop roll up door.
I have 220 power every 6’around the perimeter of my shop.
I have 2×6 walls with R-19 insulation

Thanks for your help


61 replies so far

View waho6o9's profile


8946 posts in 3455 days

#1 posted 06-05-2016 04:24 PM

Interesting system Jim. I can’t help you with your concerns but I was reading the Q&A on Amazon and it said:

Question: Can the indoor unit be mounted on a ceiling?

Answer: No, it has to be mounted on a wall, preferably 3 to 4 inches from the ceiling.
By Boca Supply on March 14, 2016

I was unaware the inside return was that close to the ceiling for install, not sure if you knew that if you were going to install it yourself.

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118142 posts in 4456 days

#2 posted 06-05-2016 04:29 PM

Yes I read that too Jimmy ,I can find a place to mount it up that high,it kind of makes sense since cool air drops down.
Thanks for making that point,it’s good to factor into the whole equation.


View waho6o9's profile


8946 posts in 3455 days

#3 posted 06-05-2016 04:34 PM

Where is Boca Supply? All I could find was this:
“Here at Boca Supply, we focus on providing our customers with high quality products shipped directly to your doorstep. In the e-commerce business since 2006, we know what it takes to keep online shoppers happy by providing quick shipping, excellent products and great customer service.

We’re a real business with an actual real store front, you can even stop by to look at our products in person to take a look at the quality before purchasing. We’d actually love to tell you more about our products in person! Our wide range of products vary from natural products to electronics such as mini splits -single zone systems, to multi zone ductless systems and even do it yourself machines. Everything we sell has independant certification and comes with a manufacturer’s warranty. “

Sounds good and all but if you need a part or a warranty call and they go belly up what do you do?
I’d feel better if they had an address with phone number and email etc….

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118142 posts in 4456 days

#4 posted 06-05-2016 04:38 PM

Never heard of them either but there’s a certain amount of protection by buying through Amazon but that’s short term,that’s why I asked for best brands by AC guys.


View TheFridge's profile


10861 posts in 2364 days

#5 posted 06-05-2016 05:30 PM

I wired a couple of these up before. I’ve heard the Mitsubishi brand was pretty good. Daikin as well. I’ve only wired up Daikin commercial models. Was told you had to follow their instructions to a T amd if not there were kinda fussy to startup. Once you got them going they were excellent.

That’s about all I know. Was told this by the AC guys installing the units.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View DocSavage45's profile


9019 posts in 3721 days

#6 posted 06-05-2016 05:31 PM


WAAAAAY LOOOOONG ago I worked in ac. So I have some rusty knowledge. I installed the heating ( forced air) in my shop. This was after I received several quotes from heating and ac folks who had their own brand to sell. I found someone who consulted and I did the rest.

I recently bought a 12000 btu ac unit window unit from Sears for the shop as it is about the size of a one car garage. We have a couple upstairs in our old Victorian house to supplement an existing and badly ducted ac unit. Mine is sized to the shop but it works too hard.

My problem where I am is extreme humidity. The unit keeps the shop area relatively cool but the humidity remains high . I humidify in the winter in my shop/small barn, and I’m looking at a dehumidifier as a supplement.

If the btu’s are too low the machine will disappoint you. And it will not meet the cooling requirements. If your ceilings are high like mine maybe you can use some reflective plastic that has come out of the aerospace program as a solution?

-- Cau Haus Designs, Thomas J. Tieffenbacher

View JBrow's profile


1368 posts in 1798 days

#7 posted 06-05-2016 05:45 PM


I am not a heating and air guy nor have I tackled the problem A/C in the shop; so for what it is worth…

The mini-split system you are considering is nice but pricey. Since you already have shop heating covered, my thought to be to first look at window A/C units. A quick look shows that Sears offers a window A/C rated at 25.000 BTUs for $600. I am sure there are other brands at this rating. Two of these units would put you over the 48,000 BTUs your estimate and still be within budget. These could be installed in existing window openings or, since you are a contractor, perhaps dedicated openings could be created (or required).

On a side note, the central A/C that services a 1000 sf apartment conked out a couple of years ago. One small window A/C in a bedroom keeps the entire apartment surprisingly comfortable in mid-80 to mid-90 degree weather. It has 8’ ceilings and R13 in the walls and maybe R32 in the ceiling.

View TheFridge's profile


10861 posts in 2364 days

#8 posted 06-05-2016 05:52 PM

The mini splits have many options as well depending on brand.

The Daikin units I wired had a central compressor outside that had 4-6 of the fan units inside tied into it. Pretty neat stuff. I believe they were wired by zones so they could come on in different sections (1 set for hall and another for each classroom). Really neat stuff.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Blackie_'s profile


4883 posts in 3391 days

#9 posted 06-05-2016 05:54 PM

Jim, have you considered a 240 window unit? The split system is going to eat up some real estate on your wall more so then a window unit.

I’m surprised to hear you’re already hitting triple digits up there in Oregon, down here in central Texas our highest this year has been but only 83 – 85 degrees, but Texas is known to have strange weather though.

-- Randy - If I'm not on LJ's then I'm making Saw Dust. Please feel free to visit my store location at

View waho6o9's profile


8946 posts in 3455 days

#10 posted 06-05-2016 06:10 PM

If it’s not too humid maybe a swamp cooler would work for you and save you some money as well.

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Jim Finn

2848 posts in 3800 days

#11 posted 06-05-2016 07:07 PM

Another rusty, former AC pro here. I have a 300 square feet shop in a west Texas desert. I installed two window units and it keeps me cool as I need when it is 100+ degrees out there. My shop is insulated. The problem with air conditioning a woodshop is the dust. Need to keep the coils clean. If you have a situation where the temp is down but humidity is still up, this can be caused by too large a unit. Sounds silly but it is true. The fix is to run that AC unit 24/7 all summer long. That will dry out the shop.

-- No PHD just a DD214 Lubbock Texas

View clin's profile


1121 posts in 1874 days

#12 posted 06-05-2016 07:09 PM

I’m not an AC expert but am an engineer and did a lot of studying on this before having a mini-split in my shop.

The ONLY, ONLY, ONLY, got that, ONLY way you can know how much capacity you need is to run a Manual J (or equivalent) calculation on the space. Many AC contractors don’t do this at all, and those that do often say they do it after you sign the contract. if the calculation says you need a larger unit, they’ll pay the difference. But, the rule of thumb calculations are almost guaranteed to oversize the system

They don’t get people calling them back when they have too much AC. So that’s why they oversize. The problem is the larger system cost you more and it will be less efficient. It will also be less comfortable. This is especially true in humid locations.

You have a 28×30 = 840 sqft shop. The rule of thumb is 1 Ton of AC per 600 sqft. So based on that you would need 1.4 Tons of AC. 1 Ton = 12,000 BTU/hr. Anything telling you you need 48,000 BTU = 4 Ton is just plain wrong. Unless your shop is un-insulated. If that’s true, insulate the shop first, then get the AC.

I’ve run a manual J on my shop and my whole house. My house is 3,600 sqft and I live in the southwest and have pretty hot summers. Manual J says I need less than 4 Tons. My house, came with 2X5 = 10 Tons of AC. Even on the hottest days, it short cycles (only runs a short time before turning off).

Like I said, AC contractors like to err on the high side.

Again, you really need to run a Manual J calculation. That term “Manual J” is because it literally is call “Manual J Residential Load Calculation” published by the Air Conditioning Contractors of America (ACCA). They are the recognized authority on heating and cooling.

You can get an Excel spread sheet from them at (it’s free no sign up or anything needed):

Now, without the actual Manual J, you really won’t have the info you need to fill in the spreadsheet. It is actually simple in concept, but very detailed. Wall thickness, siding, insulation. Type of floor, insulated slab, type of ceiling, roof etc.

You can buy it at Amazon for about $90 (that’s right they don’;t give it away). In my case I was also having AC added to part of our house and spent something like $7,000, so spending $90 and some time to make sure I got what I needed was money well spent.

My guess is they don’t make a mini-split too SMALL for your needs. Like I said the rule of thumb suggests 1.4 Tons (~16,800 BTU/hr). And that rule of thumb is almost always too much.

Okay, now for some general comments. As with an AC system, you have to drain the condensate away. So make sure you have a way to drain the water that comes from the INDOOR unit.

I did not install mine myself. Physically the installation is simple and you clearly have the experience to do that. The only real catch is you need to evacuate the refrigerant lines connecting the indoor and outdoor units. So you need a vacuum appropriate for that and the gauges to indicate the level of vacuum. This is also needed to detect leaks.

The outdoor unit will come precharged with refrigerant. So you don’t have to add any (unless your lines are real long). There are some other things you have to be careful of, like the height difference between indoor and outdoor, and I think you need to keep the refrigerant lines in some height range. Though I’m not sure. I didn’t get into those details much, once I decided to not install it myself.

If you know an AC guy, you could buy him a case of beer and have him do that final steps.

As for brands, Mitsubishi , Fujitsu, Daikin are probably the best. LG is supposed to be good, but I heard in more than one place, that parts are hard to get for those.

Be aware, that some warranties require that the unit be installed by a licensed AC contractor.

In my case I had one outdoor unit put in (on my roof) and this feeds 3 indoor units. The installation crew was two people, and they spent a good two days doing it. But perhaps you have a simpler setup where you can just place the outdoor unit on the ground outside the wall the indoor unit is attached to. Keep in mind you need to get 240 AC to the outdoor unit. The indoor units get power from the outdoor unit.

Something else to wrap you head around is the way mini-splits are meant to work. You do not typically raise and lower the thermostat. They work best running 24/7. Without starting a whole new topic, turning back a thermostat has at best a 6% reduction of energy in an ideal situation (that’s what I recalled the studies showed). Much less in more realistic conditions.

Think of a mini-split like a car cruising down the highway. As compared to a typical on-off AC system that functions like a car racing to the next red light. Mini-splits have variable speed compressors, so they can throttle back when needed rather than cycling between full on and full off.

Now, if you are a weekend warrior and know you won’t be in the shop 5 days of the week, then it would make sense to turn it off while you aren’t there. But keep in mind that sizing of AC systems is based on average heat and cooling. Not based on how quickly it can cool a space that is already really hot.

While no AC system is going to work great if your expectation is to come into a sweltering shop, turn on the AC had have it comfortable in minutes. A mini-split is particularly ill-suited to doing that.

Because mini-splits are designed to run 24/7, they don’t typically come with fancy programmable thermostats. I’m not saying none do, but I don’t recall seeing that.

In a shop, the only special thing I would keep in mind, is like any AC unit, you don’t want them filling with dust. That has not been an issue for me. But, if I know I’m going to make a lot of dust for an extended period of time (like ripping boards for an hour). I’ll just turn it off. Also, my Jet room filter happens to blow right at my mini-split, so the mini-split is typically getting filtered air blown its way. I also think being near the ceiling helps as obviously dust is going to fall downward. And with something located 4” from the ceiling, there’s not a whole lot of up for dust to fall down from.

I know I’ve thrown a lot at you, but I hope some of it made sense and is helpful.

-- Clin

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118142 posts in 4456 days

#13 posted 06-05-2016 07:10 PM

Thanks for the info Don
Thanks Tom Sounds like you have you shop handled
Yes Randy I’ve thought about that too,just not sure if more than on unit will end up fighting each other. Yes we are surprised too,these temps are breaking records for our area.
I did think of a swamp cooler Jimmy but I’m concerned about all that moisture being pumped it to my shop and rusting everything.
Thanks guys for your ideas.


View DocSavage45's profile


9019 posts in 3721 days

#14 posted 06-05-2016 07:30 PM


Thanks for your contribution to Jim’s post!

Great info! Wish I’d had it. I did calculate total volume as I have an additional triangulated space as my roof joists are the ceiling of my shop. Which is how I came up with my calculations. And that was 12,000 btu which is just adequate because I have heat loss and gain due to doors to the shop and my shop is well insulated.

A dehumidifier will keep the rust down and the ac keep me adequately cool. I usually start it up with a timer at the early/cool part of the day to make sure the cool down is over time.

Jim….Good luck!

-- Cau Haus Designs, Thomas J. Tieffenbacher

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118142 posts in 4456 days

#15 posted 06-05-2016 07:44 PM

Thanks Jim and Clin that’s a lot of great information answering a great deal of questions I had. I appreciate your links Clin but I get lost in spreadsheets never could figure them out. In considering my shop size did you take into account my 14ft ceiling as to how many BTU unit I need ?


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