Sizing mini split for detached 2 car garage

[MikeC55]

I've read through a lot of threads on the subject but would still like to get some feedback on my specific project. I'm insulating a a 24 x 24 garage, which will no longer have the 8' ceiling, but instead it will be open (via ridge beam) to the rafters. Current rafters are 2 x 8 (16" OC) and I plan to add on to them for increased depth and allow R30 insulation, insulated door, 12' x 7 and 3 small windows in other 3 walls. Roof pitch is 6/12. Climate is southwest CT (we get some snow, temps is winter can dip to single digits, but normally teens to twenties).
I've talked to a couple of direct sellers of mini splits and they're pushing 24K BTU, which seems a bit overkill to me. I'm not planning to live in the garage, just make it comfortable enough to work on cars and woodworking projects during the year.
I have also noticed there is a pretty large price spread between Mitsubishi systems and many other lesser known brands. Any non-Mitsu systems you've had good experience with? Did you DIY the install?

 

[bx24]

I have a 24x30 (10 Ft ceiling) and have an 18K btu in there. loft is 12K

I have a Mr Cool DIY (installed in 2022) that I just installed a new air handler since the old one had a leak in it. Dye is your friend and yes, Mr cool covered it under warranty. I live in the state north of you and cools and heats just fine. Leave it on freeze protection in winter

 

[PoorUB]

I've read through a lot of threads on the subject but would still like to get some feedback on my specific project. I'm insulating a a 24 x 24 garage, which will no longer have the 8' ceiling, but instead it will be open (via ridge beam) to the rafters. Current rafters are 2 x 8 (16" OC) and I plan to add on to them for increased depth and allow R30 insulation, insulated door, 12' x 7 and 3 small windows in other 3 walls. Roof pitch is 6/12. Climate is southwest CT (we get some snow, temps is winter can dip to single digits, but normally teens to twenties).
I've talked to a couple of direct sellers of mini splits and they're pushing 24K BTU, which seems a bit overkill to me. I'm not planning to live in the garage, just make it comfortable enough to work on cars and woodworking projects during the year.
I have also noticed there is a pretty large price spread between Mitsubishi systems and many other lesser known brands. Any non-Mitsu systems you've had good experience with? Did you DIY the install?

If you want to use the mini for heat it will depend on the specs of the specific unit. You need to be aware if the BTU out put at various outdoor temperatures. They all decrease heating capacity as the outdoor temp falls.

 

[aggie113]

Mitsubishi is a great brand for mini splits. I do (and would) use that brand for my house AC. For my garage, it's paying a premium for cooling. I paid a pro to install a Gree 2 ton mini split in my 30x40 insulated garage a few years back. Now looking to do my own install of another 2-3 ton unit with a DIY mini split setup from Lowes/HD. The install is pretty basic even if you pay an electrician to do the run for you. If you can manage a level and a power drill you'll be good (and a friend when putting the unit on the wall).

 

[mike93lx]

You won't need 24k for cooling but you will need it for heating. Mini's use inverters so oversizing is OK since they can throttle.

You are leaving the roof vented, right?

 

[MikeC55]

Currently, the roof has no venting, but I plan to fix that. The problem is it was built with zero eaves, so no place to install intake vents. I'm going to add eve extensions which will allow venting. I watched the Alpine install video and it seems very straightforward to install. THe only thing I don't have in terms of tools is a bottle of nitrogen for purging the lines (I do auto AC). I'm thinking to go with 18K BTU and can always fire up the kerosene torpedo heater to bring up the temp quicker, if needed.

 

[bx24]

After going to a mininsplit, you might never use kero for heating again. I did the propane and never again. Take the hit for a few beans and have heat.

And yes mininsplita are not the best at low temps but at -13f last year, not dragging out a gas heater to save $20! Lol

 

[WildBill]

The difference in cost between an 18k and a 24k is usually not very much. I would go with a 24k for the faster recovery from hot cars/open doors and the added heating capability. You can't typically oversize a mini split, it will just spool down to whatever output is needed unless it's insanely oversized.

Pioneer makes a purge can you can use on any system to flush the lines, it's like $35. https://www.amazon.com/Pioneer-Flus...nditioning/dp/B08HNGXWKP?tag=atomicindus08-20

Mitsubishi used to be the best, the last couple years we are having as many problems on those systems as we do on anything else, and they are much more expensive. Lots of control board failures, even with surge suppressors. You definitely need to add a surge suppressor at the disconnect on any mini split install.

Fujitsu and Daikin are usually pretty good. There are only a handful of other companies that make mini splits, most are rebranded Gree or Midea.

The DIY Mr.Cool units come with sealed lines so you don't need a pump or gauges to install them. I have a 24k Mr.Cool in my 24*36 shop, it's been working great for about 3 years. I think they are the only company that will warranty a non professional install.

You will want some crows foot wrenches and a torque wrench, also some Nylog. https://www.amazon.com/Refrigeratio...et-Sealant/dp/B008HOSQQQ?tag=atomicindus08-20. It lubricates the flares to help prevent galling and helps seal the connection.

 

[Notgrownup]

I have a 24x24x10 pretty well insulated. Blueridge 18k btu 18seer I believe is very efficient. The heat works well . I keep it on 80 in the summer and 62 in the winter and adjust when I use it for woodworking. Been on 24/7 for 8 years now. In CT I might think of getting a hyperheat unit. Little better for colder climates.

 

[jblnut]

If you plan to use it for heat I’d spend the bones and get one that can make heat at a temp lower than your lowest outdoor temp. All the install labor is the same and it’ll be a more functional unit.

I have a 54x72x18 farm shop and have a 24k Fujitsu in it that does awesome. A 24k in a shop your size is overkill but like others have said, it’ll throttle down. I’d go larger than smaller as it’ll heat better in the winter.

 

[kaymccampbell]

I've mostly installed Senville and Pioneer minisplit units. Looking back, they don't ****. You do have to have the proper tools. If your shop is well insulated, and you're just cooling ,12Kbtu should do it. if you want the heat too, then you'll want at least 18Kbtu.

 

[pcmeiners]

Have a 12k low temp minisplit heating/cooling my 30x36 x 10H (standard insulation) shop. Be careful in choosing your minisplit, some minisplits are advertised with the maximum output, with little to none capacity above the advertised rated output. Have Fujitsu units which output far more than the advertised output (3100-22100 btu). Also CT is in an area which drops below freezing often, I would go with a low temp split. Mitsubishi and Fujitsu are about equal as to efficiency, Fujitsu is cheaper and I have warranties on all my DIY installed units (608 certified), Mitsubishi is quieter but have stipulations for licensed "professional" installation for the warranty . Note, the 608 cert is easy to get.

https://www.goodlifehvac.ca/images/Fujitsu_LZ_Series.pdf

 

[MikeC55]

Thanks for the advice, guys.