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

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?
 
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.

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?
Click to expand...
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.)
 
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%.
 
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.

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?
Click to expand...
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.
 
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
 
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.
 
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.
 
^^^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.
 
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.

20200707_232104.jpg

Edit. Installation is not the best looking, but it works.
 
Last edited:
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 :grin:

John
 
You must log in or register to reply here.
Back
Top