Mini Split Sizing

[beerplease]

So I in central Ohio and have a 30x40 Steel Wick building,poured slab with 12 walls and a open 18' ceiling at the peak. The walls are R-13 with OSB and the ceiling is open due to the building being built with 10' on center trusses(no way to hang proper ceiling according to wick). The purlins in the ceiling do have a R13 vinyl backed insulation that I have added to the factory R5 between the purlins and the metal roof. The garage has on man door and 3 9x10 garage doors that are insulated as well, plus 3 2x3 windows. I am going a little nuts trying to correctly size a mini split system such as a Mr. Cool DIY. The online calcs for basic home use give varying answers and I even tried a simplified free manual J calc that gave me 14000 btus for cooling but 136000 for heat? Any experts out there that can help me narrow the correct sizing down? down. I really don't want to pay anyone to install a system for me but I don't want to undersize or oversize the system. The shop is only going to be used 2-3 times per week but all year round, our highs are around 90 and lows can dip into the teens on occasion. I have looked at the Mr. heater option for heat if necessary as I had great luck with the one in my old house.

 

[Fueler]

Mine is essentially the same size. I finally settled on a 36000 btu unit and darn glad I did.
I don't think you can oversize an inverter unit.
Oh, and have backup heat as these tend to get wimpy in midwest weather when the cold and wind start blowing.

 

[Jackfre]

I think the 14 is way low on cool in that type building. I normally would undersize a mini-split, but in your building, if I understand it correctly, I'd do the 36 as well.

 

[beerplease]

Ok, so a little update here, I spoke with 3 different A/C mini-split suppliers local and non-local and got 3 different answers from 3 to 6 tons due to open nature and insulation in the building. Scored a good deal on a LG 36K unit from AC wholesalers and installed it. Happy to say I finished the ceiling retrofit insulation on Sunday so the building is fully insulated with R-19 in the walls and R23 in the ceilings. Turned the unit on Monday morning and worked in 72 degree temps with outside temp of 86-88 degrees! Unit worked great and is super quiet and hopefully efficient. Now that being said above 12' or so the temp in the room is still pretty warm so I believe I would need to add another 36k or 24k unit to cool the entire building. I am going to leave the unit on for a couple days to see how long it runs and performs in these last summer days before I decide to add another unit.

 

[Jackfre]

Unless you are working above the 12' level it alone for a while and get used to how it works before jumping at something else. Cold air is heavier and more dense than warm air so the area you want cool is cool. Good!

 

[ctgoodman]

If you find you can get that air below 12' fairly chilly you may get more benefit from a couple of ceiling fans just to stir the air around.