Mini Split Install Done!

[Tim M Tuttle]

Just finished my mini split install. I did everything but the copper connections and vacuuming. Those two items I left to an HVAC tech that charged me $150. I am sitting here watching the thermometer in my shop climb and it's glorious!

[Jacob Mac]

That's awesome. I would love to hear some details on the unit, the space being heated, tye install etc.

[Tim M Tuttle]

That's awesome. I would love to hear some details on the unit, the space being heated, tye install etc.

This is the unit: https://www.pioneerminisplit.com/collections/wys/products/pioneer-18-000-btu-20-8-seer-230v-ductless-mini-split-air-conditioner-heat-pump-system-full-set

Install was easy once I figured out each step. I spent way more time looking up how to do things than actually doing them. The instructions weren't great but probably bar for the course for stuff like this unit.

Two car garage, 476 sf, insulated walls but no ceiling insulation.

I'll have a video of the install done hopefully this weekend.

[Don Jarvie]

Thanks for the info. I’m getting one this summer since waiting for my heater to cycle is no fun.

By the way insulate your ceiling. No reason to let the heat or AC get away.

[Jacob Mac]

Looking forward to the video. I am trying to figure out which mini split to get for my 3 car garage. But before that, I need to get a better seal on my garage door.

Did you give any thought to getting a Mitsubishi mini split?

[Michael Alu]

About to pull the trigger on this upgrade to the new shop within the next month or two. I'll be looking forward to the video as well.

[Jim Becker]

'Glad it went well! As I've noted previously, I'm considering making this move, too. My ceiling gets done first, however...and that's happening real soon now. :)

Question for you...does the connection from the inside unit to the outside unit have to exit the building directly behind the inside unit or can the connections be routed "up and over". I'm asking because my shop exterior walls are 8" thick block and it would be far easier to route "up and over" through the soffit or down and through the former window.

[Tim M Tuttle]

Looking forward to the video. I am trying to figure out which mini split to get for my 3 car garage. But before that, I need to get a better seal on my garage door.

Did you give any thought to getting a Mitsubishi mini split?

I looked into Mitsubishi but the comparable unit was over twice as much. I definitely went on the cheap but I was pushing my budget anyway. I hope I got the Grizzly of mini splits and not the Harbor Freight. :D

[Tim M Tuttle]

'Glad it went well! As I've noted previously, I'm considering making this move, too. My ceiling gets done first, however...and that's happening real soon now. :)

Question for you...does the connection from the inside unit to the outside unit have to exit the building directly behind the inside unit or can the connections be routed "up and over". I'm asking because my shop exterior walls are 8" thick block and it would be far easier to route "up and over" through the soffit or down and through the former window.

On the unit I bought, you can take the lineset and signal wire straight back from the unit (on either the right or left) through the wall or you can run it out either the left or right on the wall. You cant go up though. Part of that lineset bundle is the drainage tube and it needs to start going down right out of the unit. When you drill the hole through the wall you have to go at a downward angle.

You can get creative with the drain but then I believe you would be required to get a condensate pump.

[Jim Becker]

Yea, after I asked the question, I actually looked at the install manual for your unit and it was helpful in understanding the options. I suspect that "relatively speaking", other mini-split systems have similar setups. It's not actually a problem...I'll just need to locate the wall unit just low enough on the wall so the pass-through can go out via the original window opening. Depending on the physical size of the unit, it's bottom will be quite a few inches higher than the current window AC unit. Doing this will be easy since I plan on actually removing the window that's, um...embedded...inside of what is effectively a temporary wall anyway. I originally left it there thinking that someday, someone else might want the window to be a window again, but getting rid of the thing will make for a much better and less creative insulation solution. It leaks like a sieve now!

[Bill Dufour]

The lineset can go upwards but the drain has to slope down all the way. The drain can run totally separate from the lineset. If you have too the drain can be pumped uphill. But then you run into problems of float switch or pump failure causing unnoticed flooding.
When I put one on a interior wall of my bedroom I ran the lineset down inside the wall with the gravity drain. Then I separated the drain and ran it in pvc sloped to the top of the mudsill and out through the exterior wall. I insulated the drainline separately so it would not sweat and cause mold under the house. I do not really know if that was necessary or not. I have never noticed any condensation coming out the drain. But summer humidity here is very low.
Bill D

[Don Bullock]

Thank you for the information. I’m planning to add a mini-split to my 960 sq. ft. shop/garage building. Would like to know how well the Pioneer unit is working for you.

[Bill Dufour]

One tip on installing the mounting plate is to feel free to drill extra holes that line up with your studs. I had to move a few screw locations a few inches to keep it where I wanted. I used fender washers at the new locations and two screws replaced one at each site.
A real lever type tubing bender is much better then the coil spring type. I could use my car air conditioning gauge manifold set to connect the vacuum pump. You have to buy an adapter for the mini split connection($5 on the bay)
I ended up with a good used vacuum pump and flaring set for about $100. which is less then an ac tech would charge. Since the tools were mine, not rented, I pulled the vacuum and held it overnight just to be sure. You could flush the lines with any dry inert gas if you feel the need. Ar, N or CO2 are cheap
I ended up using 48" feet of tubing so I had to add about one ounce of extra freon. This was an excuse to buy an accurate electronic scale.
Bill D

[Tim M Tuttle]

Thank you for the information. I’m planning to add a mini-split to my 960 sq. ft. shop/garage building. Would like to know how well the Pioneer unit is working for you.

Working well so far. Was about 20 degrees outside when I was in the shop last night and it was a 65 in the shop. I turned it up to 70 just to see how it would do and about 10 minutes later I said "nope, too hot" and turned it back down to 64.

You can only hear the unit when you stop everything you're doing and really listen for it. The outdoor unit is super quiet as well.

It was 10 degrees this morning when I left for work and it was 60 in the shop and it's supposed to get really cold the next few days here so it will get a workout. Interested to see what my electric bill does.

[Bob Bouis]

When I did mine, I ran the drain straight down into a PVC pipe which exited separately near the floor level. I did have to cut a long narrow hole in the wall to install it this way.

[Jack Frederick]

A couple suggestions on mini-split heat pumps (mshp). I represented one of the major brands for 14 years in my business and wouldn't be without them in my home. If you are considering a mshp make sure you understand the performance limits on each model you are considering. Even within one manuf line there are different models of the same size that have different specs. Some will heat down to 5*, others will operate down to -20*. Be right on this or you are stepping into your own personal twilight zone, especially if you buy on-line. Don't oversize them. I have found that they consistently exceed expectations. On modulating equipment th low range is more important than the high. On the wall brackets, definitely anchor them to the studs, but I ALWAYS put a toggle at each corner. I have found the brackets to be so light that in order for the evap to mount nicely to the wall the toggles are necessary. So not mount them to high on the wall. 8' is about max. CLEAN THEM. A contractor will tell you to clean the filters and yes that is necessary. However those filters are not great and with wood shop dust (even with primary and secondary dust control) and the fin spacing on the coils and the fact that about 40% of the coils surface slopes down toward the back, you need to monitor the condition of the coil and prepare to clean them. It is not just the coil. The small curved blade fans load up and there goes your air flow. Also in a humid climate I would want to know how to completely remove the cover, take a can of compressed air and a shop vac and blow off/vacuum the electronic area. The current issue of FWW has an article referencing Chris Beckvoort's mshp install saying it has been trouble free. I wrote the editor suggesting it was time for a thorough cleaning. Btw, how does he keep his shop so clean?

[Jack Frederick]

Jim, you can rout the refrigerant piping up down or sideways as you choose. The drain is the problem. Mshp's are excellent at dehumidification and in Buck's Cty, you will need plenty of it. A gravity drain is desirable as a result, so you will likely have to drill the wall for that. Check the manuf spec on your evaporator to confirm the piping layout. I use Fujitsu's as I know them best. I drill the hole on the left side and move the drain to the left side. That allows the drain line to exit the building directly and makes it future accessible at the connection and easy to deal with. Also the line set goes through that hole and lays across the back of the unit, again allowing easy future access. It is a machine. Build it so you can service it. Another big advantage of putting the drain on the left is that it makes it easier to close the unit down onto the mounting bracket. With the drain line laying across the back it is a classic example of 5# in a 4# bag. You end up shoving things around trying to get the unit to close down and frequently end up trapping the drain line. DO NOT be that guy. Therein lies madness;) Flooding condensate tray, standing water, mold mildew. Running the line set out of the wall directly on the rt kinds two blocks you for future access. If you choose to pump your condensate, Aspen makes some nice mini pumps, but I find them to be annoying. On the drain connection I have found the best way to deal with them is to Use a plastic barbed fitting with hose clamp X 1/2 or 3/4" mpt plastic fitting into the pvc female adapter.

[Jim Becker]

Jack, your comments are appreciated. After looking at things more closely I should be fine with "normal" through the wall routing of everything because the upper extent of the existing window area will fall within the correct plane for connections out the back of the inside unit, either left or right side, depending on how I decide to handle one other small thing. The existing electrical run is sized correctly for cable, so that's just a matter of re-termination/extension and conversion to 240v. Outside, the drain line will not be an issue at all. The only remaining challenge is to decide whether or not to "ground mount" the external unit or wall mount it on the outside of the new wall that fills in the window opening. The building at that point is partially below grade and putting it "in" a window well is not a permitted configuration. I can do off to the side, above or below the window area on a leveled area on the slope or wall mount directly below "on" the new window wall but above ground.

[Thomas Crawford]

Jack -

Does it matter where you hang the mini-split? Say in a rectangular space should it be a on a long or short wall, centered etc?

[Jack Frederick]

I never ground mount the units. Airtec make nice wall brackets. Your unit stays cleaner longer. You will have fewer bugs. You don't have to kneel to work on it. Also, in a northern climate you want to be above the snow. When it is cold your unit will go into defrost mode periodically. The condensate that forms in the condensing unit has to drain somewhere and has to have a clear path to do so. I have seen ground mounted units build up an ice block to the point it froze those nice high efficiency fan blades in place. Don't be that guy. I have seen ground mounted units that the face of the coil was mudded solid from the splash from rain and flooding gutters. Raise it up.

[Hoang N Nguyen]

I just got a 3 zone Mitsubishi 24k BTUH 20 SHEER system installed in my basement shop last week and I'm LOVING not walking into a 55 degree shop during the winter. I hired a Mitsubishi diamond contractor to install mine, My knowledge of HVAC is zero to none so I didn't want to mess with it. Although, now that I've seen how they did it, I wish I would have done it myself because it looked so easy. The one perk of having a Mitsubishi diamond contractor do my install is that Mitsubishi extends my warranty from 10 years to 12 years. The contractor ran all my copper lines up the walls and along the ceiling joist and all 3 lines exit the house at one location where the outdoor unit is. 2 of my condensate drain lines were ran along my walls, drilling through the studs to connect together before existing to outside. Last line was drained into my sink with it's own P trap.

I opted for the FH series which has automatic vanes that move up and down as well as side to side on it's own. It also has an optical eye at the bottom right corner of the unit that scans for movement within the room and focus the vanes at that location.

I have no experience with any other brands but for those that are considering the Mitsubishi units, I highly recommend them. Although I've only had mine for a week, I'm really loving it so far. It's super quite when it runs and heats up my 1600 sq. ft. basement shop from 55 to 65 degrees in about an hour. The 12 year warranty is a big bonus.

[Jack Frederick]

First off, follow the manuf installation instructions. These units depend upon air circulation to work so don't build them in to a confined space. Also, pay attention to the line set requirements. Some manuf have minimum one set lengths. .

[Mike Hollingsworth]

Jim, you can rout the refrigerant piping up down or sideways as you choose. The drain is the problem. Mshp's are excellent at dehumidification and in Buck's Cty, you will need plenty of it. A gravity drain is desirable as a result, so you will likely have to drill the wall for that. Check the manuf spec on your evaporator to confirm the piping layout. I use Fujitsu's as I know them best. I drill the hole on the left side and move the drain to the left side. That allows the drain line to exit the building directly and makes it future accessible at the connection and easy to deal with. Also the line set goes through that hole and lays across the back of the unit, again allowing easy future access. It is a machine. Build it so you can service it. Another big advantage of putting the drain on the left is that it makes it easier to close the unit down onto the mounting bracket. With the drain line laying across the back it is a classic example of 5# in a 4# bag. You end up shoving things around trying to get the unit to close down and frequently end up trapping the drain line. DO NOT be that guy. Therein lies madness;) Flooding condensate tray, standing water, mold mildew. Running the line set out of the wall directly on the rt kinds two blocks you for future access. If you choose to pump your condensate, Aspen makes some nice mini pumps, but I find them to be annoying. On the drain connection I have found the best way to deal with them is to Use a plastic barbed fitting with hose clamp X 1/2 or 3/4" mpt plastic fitting into the pvc female adapter.

I've done more than ten of these.
This guy knows what he's talking about.

[Peter Kelly]

I just got a 3 zone Mitsubishi 24k BTUH 20 SHEER system installed in my basement shop last week and I'm LOVING not walking into a 55 degree shop during the winter. I hired a Mitsubishi diamond contractor to install mine, My knowledge of HVAC is zero to none so I didn't want to mess with it. Although, now that I've seen how they did it, I wish I would have done it myself because it looked so easy. The one perk of having a Mitsubishi diamond contractor do my install is that Mitsubishi extends my warranty from 10 years to 12 years. The contractor ran all my copper lines up the walls and along the ceiling joist and all 3 lines exit the house at one location where the outdoor unit is. 2 of my condensate drain lines were ran along my walls, drilling through the studs to connect together before existing to outside. Last line was drained into my sink with it's own P trap.

I opted for the FH series which has automatic vanes that move up and down as well as side to side on it's own. It also has an optical eye at the bottom right corner of the unit that scans for movement within the room and focus the vanes at that location.

I have no experience with any other brands but for those that are considering the Mitsubishi units, I highly recommend them. Although I've only had mine for a week, I'm really loving it so far. It's super quite when it runs and heats up my 1600 sq. ft. basement shop from 55 to 65 degrees in about an hour. The 12 year warranty is a big bonus.Thanks, am planning on getting the same for the upper floor of my house. Is this a P or M-series unit? What does the 12 year warranty cover? Parts? Just the compressor? Also, how did you locate a Diamond installer? Does the unit need to be purchased through one to get the extended warranty?

[Hoang N Nguyen]

Thanks, am planning on getting the same for the upper floor of my house. Is this a P or M-series unit? What does the 12 year warranty cover? Parts? Just the compressor? Also, how did you locate a Diamond installer? Does the unit need to be purchased through one to get the extended warranty?

Hi Peter, I want to say I have the M series since all my units have their model# starting with the letter MSZ. I can confirm this with my contractor tomorrow.

The 12 year warranty from Mitsubishi covers parts and compressor minus labor, my contractor offers 2 year labor coverage. He said 2 years is more then what most contractors will offer but he wanted his customers to go through 2 cooling and heating cycles just in case.

If you go through the Mitsubishi website and inquire about their units, they will have a diamond contractor in your area come out to provide quotes as well explain their product. All diamond contractors are trained by Mitsubishi, which is why they offer an additional 2 year warranty.

[Jim Becker]

Tim, how did you find a local HVAC tech to do the final work for you? The firms around here look at you like you have two heads if you ask for a "final install only" type quote. They want the whole deal or nothing it seems...

[Tim M Tuttle]

Tim, how did you find a local HVAC tech to do the final work for you? The firms around here look at you like you have two heads if you ask for a "final install only" type quote. They want the whole deal or nothing it seems...

I made a post on Nextdoor.com asking if anyone knew an HVAC tech that might be able to help me. I got a reply from a contractor who uses a guy on a lot of his jobs. Your best bet probably is to find a guy that will do side work or someone who works on his own.

[Bill Dufour]

A car ac guy should be able to do the simple connect and vacuum for a mini split. But they may not own the cheap adapter to connect the smaller service port used on mini splits.
I do not know how many car ac folks even do copper flaring. I think most all car connections are factory connectors with O-rings.
Bill D

[Jim Becker]

A car ac guy should be able to do the simple connect and vacuum for a mini split. But they may not own the cheap adapter to connect the smaller service port use don mini splits.
I do not know how many car ac folks even do copper flaring. I think most all car connections are factory connectors with O-rings.
Bill D
True, but there are warranty implications on who does/signs off on the install for many of the manufacturers. Having someone with proper certifications is helpful with that.

[Brad Adams]

As an HVAC contractor I wouldn’t quote a final install only either. I don’t think you guys realize how expensive it is to maintain and keep a business running with all the regulation we have with licenses, insurance, and everything else that goes with it.
Once we touch it we are liable.
As an example, many years ago, I installed a gas line to a vent free heater in a shed that was converted to a woodworking shop. The homeowner bought and installed the unit, I just installed the gas line. A year later I received a letter in the mail that my insurance company was contacted by his insurance company to pay for damages caused by mold. The guy kept the unit on all the time with no ventilation causing black mold due to all the moisture it put out. Had I not wrote on my invoice that the owner was warned of the dangers of running a vent free heater I would have had to pay the damages. Even then it took a lawyers letter to get them to back off.
Don’t tell me that you won’t hold me liable, it isn’t you that will do it. Your insurance company won’t bat an eye at trying to get out of paying the bill for damages without you even knowing about it.

[Jack Frederick]

My experience in DIY jobs of this type, and keeping Brad's position in mind, is that you end up paying one way or the other. If you supply the machinery, the labor bill increases to cover the contractors costs, and they are substantial and that is fair. Perhaps a way to handle this is to ask if the contractor will allow you to mount the condensing unit and the interior mounting bracket only, drill the holes and have the 220v disconnect located. He supplies the equipment, does the secret sauce and gets off the job in one piece. In order for this to work, the contractor has to be able to make it a single call. In and out. If you do this work, take photos and go see the contractor to show what is in place before he shows up. Most hvac contractors are slammed with work. Something like this might work out. Brad?

[Tim M Tuttle]

My experience in DIY jobs of this type, and keeping Brad's position in mind, is that you end up paying one way or the other. If you supply the machinery, the labor bill increases to cover the contractors costs, and they are substantial and that is fair. Perhaps a way to handle this is to ask if the contractor will allow you to mount the condensing unit and the interior mounting bracket only, drill the holes and have the 220v disconnect located. He supplies the equipment, does the secret sauce and gets off the job in one piece. In order for this to work, the contractor has to be able to make it a single call. In and out. If you do this work, take photos and go see the contractor to show what is in place before he shows up. Most hvac contractors are slammed with work. Something like this might work out. Brad?

I was all in for $1500 by doing the majority of the install myself. That wouldn't even cover the unit if I went with Mitsubishi and I was looking at probably another $1000-2000 for installation. I am well aware that I didn't get as good of a unit as a Mitsu but it was either this or nothing. For now at least.

[Bob Bouis]

I'm not sure of the legalities of it where you live, but mini split installs are easy DIY work and the tools for hooking one up (vacuum pump, micron gauge, mini split adapter, hoses or gauges, flare tool, and...uh...wrench...) cost less than hiring someone to do it.

You don't get a warranty but with generics they're not worth anything anyway.

[Tim M Tuttle]

I'm not sure of the legalities of it where you live, but mini split installs are easy DIY work and the tools for hooking one up (vacuum pump, micron gauge, mini split adapter, hoses or gauges, flare tool, and...uh...wrench...) cost less than hiring someone to do it.

You don't get a warranty but with generics they're not worth anything anyway.

The manufacturer of my unit warrants DIY installs.

There's also Mr Cool units which are made specifically for DIY installs. The only problem with those is that you may have excess lineset rolled up next to the outdoor unit.

[Robert Hayward]

mini split installs are easy DIY work and the tools for hooking one up (vacuum pump, micron gauge, mini split adapter, hoses or gauges, flare tool, and...uh...wrench...) cost less than hiring someone to do it.

That was what my calculations for the cost of my self installed mini showed when I was thinking about a mini. I even bought pro grade tools to do the job, just to be safe. An eccentric flaring tool and torque wrench with the proper wrenches to fit my flare nuts. Around here the auto parts stores will give for free the vacuum pump, gauges and hoses with a credit card deposit equal to the value of the stuff you are walking out of their store with. Keep them as long as you need them, return them and they refund the deposit.

The compressors are pre charged with freon and the compressor unit has valves built in to it. After you pump down the lines and evaporator just open the freon valve and you are done.

Please note that I have an extensive construction background ( not A/C though ) so the install may have been easier for me than someone never involved with the trades.

[Steve Catts]

Tim,
I've been looking at the Pioneer units as well - price is great and the warranty is reasonable. I see you got the unit with the high SEER rating at 20.8 which runs almost $300 more than their 17 SEER unit. If the primary difference is energy efficiency, the cost to operate is only a few bucks a year difference. What am I missing that would make the more expensive unit worth the extra cost?

I have a 500 sf +/- garage in Houston. 9' ceiling. Well insulated. Two exterior walls with brick. No windows. Two single doors - pretty well sealed. Most of the 'rule of thumb' tables suggest a 12,000-BTUh unit. The Pioneer 12k unit ranges from 4500BTUh to 16700BTUh. I don't want to come up short but also know that oversizing can be a problem. Can anyone offer some thoughts about if the 12k will do or do I need to upsize to the 18K (7600BTUh to 24800BTUh)?

Thanks! I don't want to get this wrong!
Steve

[Tim M Tuttle]

Tim,
I've been looking at the Pioneer units as well - price is great and the warranty is reasonable. I see you got the unit with the high SEER rating at 20.8 which runs almost $300 more than their 17 SEER unit. If the primary difference is energy efficiency, the cost to operate is only a few bucks a year difference. What am I missing that would make the more expensive unit worth the extra cost?

I have a 500 sf +/- garage in Houston. 9' ceiling. Well insulated. Two exterior walls with brick. No windows. Two single doors - pretty well sealed. Most of the 'rule of thumb' tables suggest a 12,000-BTUh unit. The Pioneer 12k unit ranges from 4500BTUh to 16700BTUh. I don't want to come up short but also know that oversizing can be a problem. Can anyone offer some thoughts about if the 12k will do or do I need to upsize to the 18K (7600BTUh to 24800BTUh)?

Thanks! I don't want to get this wrong!
Steve

Hey Steve,

I went with the higher efficiency unit because it will still heat when the outside temp drops to as low as -13. The other unit only heats down to 5 I think.

As far as sizing goes, I recommend calling Pioneer and giving them the specs of your garage. They will then be able to size the unit appropriately. Load questions are a little out of my wheelhouse.

[Bob Bouis]

Keep in mind that most a/c sizing guides are oriented toward residences that are climate controlled 24/7. It depends on how you're heating and cooling your shop and your personal preferences as to comfort, but you're often better off oversizing a mini split so you can quickly bring the temperature to your comfort level. They automatically slow down to as little as 1/2-to 1/3 the full load capacity when it's not needed.

A lot of people think it's more efficient to set your thermostat at one place and keep it there -- that's bunk. The unit is at its most efficient when it runs full blast without stopping, and it rate of heat exchange between inside and outside [and thus the total BTUs required] depends on the difference in temperature over time.

[Bill Dufour]

The flare nuts are a wierd size. Not really metric not really English. I think I ended up using one metric and one English wrench at the same time. I bought crowfoot wrenches ahead of time to use with my torque wrench. For the big pipe I bought a tubing bender. much better then the spring type bender.
Bill D

[Steve Catts]

Great! Being in Houston will allow me to avoid that -13 issue! Although this last winter makes me wonder! I'll call Pioneer.

[Jack Frederick]

The manufacturer of my unit warrants DIY installs.

There's also Mr Cool units which are made specifically for DIY installs. The only problem with those is that you may have excess lineset rolled up next to the outdoor unit.

If if there is excess line set you do not want to leave it coiled. It will trap oil in the low spots. Lay off excess line set in a serpentine fashion.

[Thomas Crawford]

Great! Being in Houston will allow me to avoid that -13 issue! Although this last winter makes me wonder! I'll call Pioneer.

Interested in what you come up with, especially on the oversizing. Trying to figure out a unit in the next week and a half or so.

[Bob Bouis]

I've been looking at the Pioneer units as well - price is great and the warranty is reasonable. I see you got the unit with the high SEER rating at 20.8 which runs almost $300 more than their 17 SEER unit. If the primary difference is energy efficiency, the cost to operate is only a few bucks a year difference. What am I missing that would make the more expensive unit worth the extra cost?

Efficiency is not a good reason to get high seer units for a shop if you're not going to cool it 24/7.


I have a 500 sf +/- garage in Houston. 9' ceiling. Well insulated. Two exterior walls with brick. No windows. Two single doors - pretty well sealed. Most of the 'rule of thumb' tables suggest a 12,000-BTUh unit. The Pioneer 12k unit ranges from 4500BTUh to 16700BTUh. I don't want to come up short but also know that oversizing can be a problem. Can anyone offer some thoughts about if the 12k will do or do I need to upsize to the 18K (7600BTUh to 24800BTUh)?

The rule of thumb is really off here. For starters that BTU range probably isn't what you think it is; IIRC it's the max and min btus the thing will put out while running full blast in varied environmental conditions. Air conditioners are heat pumps, so they produce less cooling the hotter it is outside. Cool temperatures inside also reduce efficiency.

For 500 sq ft that was used intermittently as a shop I would go with 24k. 18k would be the minimum.

[Bob Bouis]

If I can elaborate. The reason mini splits have such high efficiency ratings is that they're really good at keeping a space 78 degrees over the course of a year, all day and all night (hence "SEER, seasonal energy efficiency ratio [or whatever it stands for; the first word is seasonal]. The SEER test is designed for continuously occupied spaces. "Seasonal" cooling is mostly low demand where the variable speed of the mini split makes it very efficient. When a mini split runs full blast on a hot summer day, they generally aren't any more efficient than any other air conditioner [look at the EER rating].

If you're just using the thing to make your garage cool when you want to work in it, you're better off getting a bigger, nominally less efficient air conditioner so you can bring the temperature to where you want it fast. It's not just more convenient, it's more efficient. The reason is that the BTUs required to keep a space a certain temperature depend on the difference between the indoor and outdoor temperatures over time, and the total BTUs and thus total energy use depend on time. So, all things being equal, it takes the same amount of btus to keep your garage 30 degrees cooler than the outside for 8 hours as it does to keep it 10 degrees cooler for the whole day. I know which one I'd rather have for my garage. Now, that might be a bit misleading as the a/c efficiency falls off somewhat as the temperature difference increases, you don't set your thermostat based on temperature difference, etc., but it's a real consideration. If you have to run the a/c for 4 hours to get it to the temperature you want you've had a lot more heat transfer back into your shop during that time than you would if you'd spent 1 hour doing it with a bigger unit -- less efficient (not to mention a PITA).

Of course running the a/c 24/7 helps to control humidity (though not very well; get a separate dehumidifier). Dehumidifiers raise the temperature a little which lowers relative humidity. Air conditioners obviously lower the temperature which raises it. And the most humid time of the day is the coolest (early mornings, it's where dew comes from). Two strikes against air conditioners as dehumidifers.

[Robert Hayward]

I have no schooling regarding HVAC sizing, efficiencies or anything else related to it. With that said, before I did my mini for my garage shop I asked a commercial chiller expert friend for advice. I was more or less told to get one ton at the highest SEER in my price range. Running the thing 24/7 here in the Tampa Bay area my electric bill went up $25 in the month of August, the hottest month. Less in other months.

[greg Forster]

My mini split has 15’ lineset; is it best to install total 15’ or can I cut the Lineset shorter?
i can locate outdoor unit to use 8’ to 15’ of line set

[Bob Bouis]

Best to cut the line set.

The manufacturer may specify a minimum lineset for whatever reason. Check their documentation or contact them and ask. In mine if you go under 8 feet IIRC you needed to remove one ounce of refrigerant.

[Jim Becker]

Bob is correct...you need to check with the manufacturer. Some units seem to have a 10' minimum. The Daikin being installed in my shop next week can go as low as something like one meter which is about all that will be needed for my install due to the exterior elevations at that corner of my shop and the wall being partially below grade.