# Anybody in or around Texas using mini-split A/C



## Investigator (May 3, 2020)

I'm reading lots of stuff about mini-split A/C systems, really wanting to compare for my area.  How well do they work for metal buildings with spray foam?  I'm looking at building a 30x40x12, with 1" of closed cell foam.   I'm just southeast of DFW.


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## Boswell (May 3, 2020)

I installed a Mini Split in my 17 x 36 metal shop. I have 8" of closed cell on the ceiling and 6" on the walls. It was installed in January so I have not made it through the summer yet but so far it has been perfect. No problem maintaining temperature. I do have a large oscillating fan that keeps the air moving and adds to the comfort level but so far, no complaints. Waiting to see how it does when it is 105F outside.


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## Investigator (May 3, 2020)

Boswell said:


> I installed a Mini Split in my 17 x 36 metal shop. I have 8" of closed cell on the ceiling and 6" on the walls. It was installed in January so I have not made it through the summer yet but so far it has been perfect. No problem maintaining temperature. I do have a large oscillating fan that keeps the air moving and adds to the comfort level but so far, no complaints. Waiting to see how it does when it is 105F outside.



8" of closed cell?  Wow!  Did you mean open cell? I've never heard of closed cell that thick.


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## Boswell (May 4, 2020)

Nope closed cell. it was expensive but I believe that insulation is one of the best places to invest when it comes to climate control.  My house has 12" thick , thermally broke walls with fiberglass insulation and IR barriers on the East, West and Roof.  Solar Cells provide 85% of all power.  I realize that it is non-conventional .


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## Hobby_5 (May 4, 2020)

Metal workshop is 24’ x 48’ but with an interior wall dead in the middle making two 24’x 24’ shop bays each with 15’ ceiling and open trusses here.  Metal building with closed cell insulation I run a Mr Cool DIY mini-split in each bay.


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## Investigator (May 4, 2020)

Boswell said:


> Nope closed cell. it was expensive but I believe that insulation is one of the best places to invest when it comes to climate control.  My house has 12" thick , thermally broke walls with fiberglass insulation and IR barriers on the East, West and Roof.  Solar Cells provide 85% of all power.  I realize that it is non-conventional .





Hobby_5 said:


> Metal workshop is 24’ x 48’ but with an interior wall dead in the middle making two 24’x 24’ shop bays each with 15’ ceiling and open trusses here.  Metal building with closed cell insulation I run a Mr Cool DIY mini-split in each bay.



What size mini splits are you guys using?  Trying to figure what is enough, what is too much, and what is way undersized for what I want.


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## Bob Korves (May 4, 2020)

Boswell is on the correct track.  It is better to keep the heat out (or in during the winter) than wasting energy over time removing (or adding) the heat.  It is a matter of pay more now or pay a lot more later, not to mention the comfort issues...


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## Stonebriar (May 4, 2020)

I don't run a min-split, but I have a 40x60x12 with 2" closed foam here in Granbury.  The building doesn't get all that cold in there, down in the mid 50's, but will get plenty hot, 90's if not regulated.  I have a 5 ton heat pump. And it is very easy to keep in the range I like.  With short run times.  When not working i keep it between 85-65.  It hasn't been that expensive to run at all.  The foam is WONDERFUL.

I would get* at leas*t 36000btu unit it is suppose to cover 1200 to 1500 sqft.  That is usually calculated with a 8' ceiling.


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## RJSakowski (May 4, 2020)

The required size of the A/C unit will depend on the u value of the enclosure.  There are online calculators to assist.


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## Hobby_5 (May 4, 2020)

Mine are 36k BTU for 24' x 24' with 15' ceilings and 3" of closed cell on ceiling with 2" on the walls.  I do have a 12'H x 16'W commercial rollup door on the west wall which is insulated as well.  The mini split does a great job and my humidity levels stay around 43 - 53 percent level.


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## Forty Niner (Jun 24, 2020)

Another QUESTION about Mini Splits in Austin Texas area.  

I have a two car attached garage with an insulated door,  one wall shared with the house, and two limestone veneer outside walls that are not insulated.   The garage has two standard sized double paned windows.  The ceiling above is the shared attic space with the house, and has blown in insulation over the garage ceiling.

My AC contractor has proposed to install a Mitsubishi 12,000 btu combo ac and heat pump.  He measured the space and said the 12k unit would do and that it is not a good practice to oversize.
My question is:  Should I bump that up to the 14/15k unit size?


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## Bob Korves (Jun 24, 2020)

Forty Niner said:


> Another QUESTION about Mini Splits in Austin Texas area.
> 
> I have a two car attached garage with an insulated door,  one wall shared with the house, and two limestone veneer outside walls that are not insulated.   The garage has two standard sized double paned windows.  The ceiling above is the shared attic space with the house, and has blown in insulation over the garage ceiling.
> 
> ...


Your contractor is correct.  You ideally want your unit to run full time on the hottest and coolest days of the year, it is less expensive to purchase and much more efficient (and more comfortable.)


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## wrat (Jun 24, 2020)

While I hate to disagree, I must.

He may have measured the size, and of course he was correct, but did he account for the R-factor in each of the uninsulated walls?
Further, how could he (or even yourself) account for the heat load in that area?  Machines?  Welders?  Boiling cauldrons of hydroxide?  (Hey, I don't know whatcha do.)
In a living area with a couch and TV, the usual formulas work fine, and there I agree completely and would tell you to listen to the contractor first.  

But in a chaotic utility area (you really need to insulate first before anything) it's never a bad thing to buy more than you think you need.  Simply because it will always get a little hotter than "average" and the machine like all machines, will only get less effective as time goes on.

Not 20k or 30k BTU, but I think your instincts are correct to bump it up 20%.


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## RJSakowski (Jun 24, 2020)

Forty Niner said:


> Another QUESTION about Mini Splits in Austin Texas area.
> 
> I have a two car attached garage with an insulated door,  one wall shared with the house, and two limestone veneer outside walls that are not insulated.   The garage has two standard sized double paned windows.  The ceiling above is the shared attic space with the house, and has blown in insulation over the garage ceiling.
> 
> ...


The reasoning behind not oversizing is to prevent too short a duty cycle.  A short duty cycle will not properly clear accumulated moisture.  My 18K Mr. Cool has a VFD on the pump and once the target temperature is reached, the pump slows down to an idle.  Since it continues to run, it  clears the moisture.  I am cooling a 350 sq. ft space with 8' ceilings with no problems so far, holding at 74ºF with outside temperatures peaking in the high eighties or low nineties.  There is also  an unconditioned space around the perimeter and overhead that routinely reaches over 100ºF due to solar heating of the roof,  Most of the time, the unit is just idling.


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## Forty Niner (Jun 30, 2020)

It is nice to have this forum to go to.  I read all the postings about cooling shops and garages to work in, and finally made my decision based on the information garnered here on this forum.  Thanks.

The installation of the Mitsubishi 15,000 btu mini split was done yesterday.  It has several run modes including a dehumidify mode.  We have some 100 degree days coming up this week and I am so happy to know that I can tinker in my garage/shop without breaking a sweat.   And I am pleasantly surprised at how quiet the unit is.  

For those who like details the Mitsubishi mini split heat pump unit::
MSZ-GL15NA inside
MUZ-GL15NA outside


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## 7milesup (Jun 30, 2020)

The largest Delta on investment is made in insulation.  We just built a new house this past year and filled the walls with closed cell foam and triple pane windows.  Many other energy conserving strategies also.  We spent about $600 over winter on LP (one of the more expensive heat sources but that is one of my only options).  There were many days that were well below -10F here.  
I too am installing a mini split in my 36x36 shop. I am installing an 18k BTU unit, Friedrich brand.   My friend has two in his much larger shop.  They are the bees knees when it comes to comfort. 
As others have pointed out, the overall sizing depends on how heat and/or cooling load.  I can't imagine heating or cooling an uninsulated space.  Sizing so that it does not cycle on and off continuously is key as RJ pointed out.  
Good luck and let us know how it goes.


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## arvidj (Jul 7, 2020)

I need to make the same decision. Minneapolis Minnesota so hot and humid on the worst summer days and teens and twenty below on the worst winter days. Natural gas 95% efficient condensing boiler with in-slab radiant for the heat. But need to select a Mitsubishi mini-split for cooling. 

Building is 24 x 36 x 18 with R-23 ... soon to be R-33 in the ceiling, R-23 in the walls and R-20 under the slab. My on-line calculations suggest 5,000 btu cooling but that sounds way too low. The contractor suggests either the 12,000 or the 15,000 will be fine for cooling with the 15,000 providing more heat than the 12,000. My calculations suggest the trade-off for heat is about 35 degrees where the btu's from natural gas are cheaper than the electricity to get the 'free' btu's from the heat pump.

So I am very interested in how your 15,000 works in a bigger building and a slightly warmer (high 80's, low 90's, 80%+ humidity here for the last few weeks) climate. Please share your experiences.


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## 7milesup (Jul 7, 2020)

^^^Arvidj^^^
I have had my mini split installed now for about a week.  18,000 BTU Friedrich.  Purchased from these guys. Very good service.

As mentioned above, my shop is 36x36 with 11ft ceilings.  R19 walls.  I have maybe R35 or so in the ceiling, although part of it has only R-10 or because I ran out time when insulating and haven't had a chance to get back to it.
The 18k BTU unit is doing very well in this heat and humidity we are currently having up here (I live 2 hrs East of you).  I would not want much less than the 18k unit though.  5000BTU wouldn't come close to keeping your place cool.  Did you account for windows and doors.  Most windows are about an R-3 at best.
I am curious what make and model of boiler you have.  I have the tubes installed but no boiler yet.


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## Bamban (Jul 8, 2020)

I live NW Austin, Williamson County. Two months ago I had this 1 Ton unit installed in my fully insulated (ncluding the garage door) standard 2 car garage. It maintains the setpoint at 75. Tall 14 oak trees in the backyard shield the house from the afternoon sun. The garage facing East, plus oak trees canopy over the driveway helps. 




Edit. Installation is not the best looking, but it works.


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## matthewsx (Jul 8, 2020)

That's what you need, cool air blowing directly on you while you work. Sure, you can cool the whole space but if you're mostly standing in one place just make it comfortable where you plan to be.

BTW, I'm definitely a fan of mini-splits but for my garage in Michigan I just have a window unit over my bench. Here in Santa Cruz I just open the garage door 

John


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## Bamban (Jul 8, 2020)

matthewsx said:


> That's what you need, cool air blowing directly on you while you work. Sure, you can cool the whole space but if you're mostly standing in one place just make it comfortable where you plan to be.
> 
> BTW, I'm definitely a fan of mini-splits but for my garage in Michigan I just have a window unit over my bench. Here in Santa Cruz I just open the garage door
> 
> John




Unfortunately the only space to mount the mini split is where it is. When doing some work the 920 right in front of the unit gets too dang cold. 

When I close the garage after working with it open, I run the floor fan to move and condition the air till the mini-split gets to set point, then turn it off. One picture is looking towards the door where I normally work. The other one is looking back towards the unit. 





Santa Clara? I do miss Marina by the ocean weather. Lived there till my Uncle said, he wants me back in 72. Wife is from Salinas.


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## arvidj (Jul 9, 2020)

7milesup said:


> ^^^Arvidj^^^
> I have had my mini split installed now for about a week.  18,000 BTU Friedrich.  Purchased from these guys. Very good service.
> 
> As mentioned above, my shop is 36x36 with 11ft ceilings.  R19 walls.  I have maybe R35 or so in the ceiling, although part of it has only R-10 or because I ran out time when insulating and haven't had a chance to get back to it.
> ...



Apologies to Investigator. I don't want to hijack his thread and am very interested in his and Fouty Niners experience.

7milesup, thanks for the feedback.

I was using the calculator found here loadcalc.net. Windows were easy ... there are none. 2 doors, one 7 x 4 insulated steel "people door" and a 7 x 9 insulated 5 panel sectional overhead. Both have an additional 4 inches of FOAMULAR glued to the inside face so at least R-20.

I had the boiler installed by a heating contractor the building slab and framing contractor recommended. The slab and framing contractor was excellent but the heating contractor ... not so much. However the boiler, installed, was about half the price but most of that decrease seemed to be labor and, sadly, that is about what they were worth.

They installed this Lars Mascot FT 80,000btu 95% efficient condensing boiler. What is interesting is that the contractor originally calculated 60,000btu as the need and a 60,000btu boiler was quoted and available. By the time I got around to the installation an 80,000btu was delivered and installed as the 60,000btu was no longer available. And now I see that 100,000btu is the smallest available.

Anyway, the 80,000btu seems to work out just fine. I have the thermostat set at 67. The slab is always warm to the touch. The initial reaction when entering the building is "not warm, but certainly acceptable" but after a few minutes of activity it becomes "comfortable" on the first level and "warm" on the 12 x 36 second floor that is 10 feet above the first level.

The modulation of the boiler is based on an outside temperature sensor and some configuration settings on the boiler controller. I was not able to discover a workable configuration setting so the boiler is binary ... 100% on or 100% off. I paid a different heating contractor to come out and inspect the work I had to redo related to the combustion air in, exhaust air out and condensate removal plumbing the original contractor had screwed up. As part of the inspection I asked about configuring the modulation settings. His response was that, in his personal experience with heated slabs, modulation is not effective. Just forget about it and leave it binary. I guess that makes sense as the outside temperature will have significant swings over a 24 hour period while the ability to quickly alter the temperature of 18 yards of concrete to follow the outside dynamics is limited.

As an example, I accidentally turned the gas valve off in early December. I didn't go into the building for a couple of days. When I finally did go back there I noticed it was cooler than expected but it had only dropped to 64 degrees. The boiler had 'faulted' 10 times based on no gas and then turned itself off. The slab was cool but not cold even after several days without heat.

One of the forthcoming challenges will be getting the boiler and the dynamics of heating the slab based on a thermostat that measures inside air temperature to work well with the heat pump that is heating the air directly. I've had bad dreams about needing a slab thermostat to make it all play well together.


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## Forty Niner (Jul 9, 2020)

arvidj said:


> I need to make the same decision. Minneapolis Minnesota so hot and humid on the worst summer days and teens and twenty below on the worst winter days. Natural gas 95% efficient condensing boiler with in-slab radiant for the heat. But need to select a Mitsubishi mini-split for cooling.
> 
> Building is 24 x 36 x 18 with R-23 ... soon to be R-33 in the ceiling, R-23 in the walls and R-20 under the slab. My on-line calculations suggest 5,000 btu cooling but that sounds way too low. The contractor suggests either the 12,000 or the 15,000 will be fine for cooling with the 15,000 providing more heat than the 12,000. My calculations suggest the trade-off for heat is about 35 degrees where the btu's from natural gas are cheaper than the electricity to get the 'free' btu's from the heat pump.
> 
> So I am very interested in how your 15,000 works in a bigger building and a slightly warmer (high 80's, low 90's, 80%+ humidity here for the last few weeks) climate. Please share your experiences.


Since the installation of the Mitsuishi 15k unit, my garage has been a pleasure to be in.  We've had 100 degree days and the unit keeps the place cool.  I find that after the initial cool down, the unit has no problem keeping the space as cool as I want.  The unit, although arguably oversized, has the ability to idle down to a whisper quiet  and maintain a very comfortable temperature.  It even cools when the "dehumidify" MODE is selected and you can hardly hear it.  I don't run the unit all the time.  I run it when I'm going to be working in the garage, and it has no problem cooling down a very hot area in less than a hour.

However, I think the climate conditions in Minnesota are quite different from central Texas.  So, maybe it is best to solicit experience from people with similar climate.


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## sru_tx (Jul 10, 2020)

This is perfect timing.  I've been eyeing (more like lusting) the minisplits for quite a few summers. I'm getting some electrical panel work done and am making provisions to add a ductless system to my small garage.

My lathe, mill, beadroller, and other clean work is done in the garage apartment upstairs.  I'm looking at the ductless system to condition the downstairs garage area where I do my "dirty" work (welding, grinding, woodworking) which makes dust.  I have an overhead Jet-brand air filtration unit to circulate air and filter, but try as I might to keep dust to a minimum, there's still a lot of dust flying around.  

Question:
How well would one of these systems handle the dust?  Obviously keeping unit's filter clean is a must.

thanks.


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