should I get these mini-splits?

[jpcjguy]

Hi all,

So I am finishing up my detached - meaning final wiring and prepping for insulation and drywall. Longer term thought was to do mini-splits down the road, but my buddy who is also building a detached is getting what appears to be a good deal on a pair of mini-splits and I can get the same deal.
They are Mitsubishi MUZ-WR24 and I can get them for 1500 a piece and 500 a unit for install.
My garage is 48x30 with combination attic and scissor truss. See pic below. I am not sure if I should go with one big unit or two smaller. The units have to be on the back wall from an aesthetic perspective for the wife. I have mocked up red boxes on the pics to show rough area of the indoor units.
I guess the units are on sale through the end of the month so I have to decide somewhat quickly. I have not researched this with the idea of pulling the trigger so soon, but figured you all could help!

Thanks

 

[Jackfre]

I cannot tell you how many times I have been told by a contractor/consumer that his wife would not like the looks of a mini split. About 24 hrs after they begin running the complaints would disappear. They become one of the things we live with.
You will, assuming good insulation and sealing, have plenty of capacity with 2-24’s. It is also best to do the rough-in at this point. Do not run them while sheet rocking. They are not construction heaters. Once everything is done, fire them up. Otherwise wrap them in plastic to keep all the construction debris out of them.

 

[jpcjguy]

I cannot tell you how many times I have been told by a contractor/consumer that his wife would not like the looks of a mini split. About 24 hrs after they begin running the complaints would disappear. They become one of the things we live with.
You will, assuming good insulation and sealing, have plenty of capacity with 2-24’s. It is also best to do the rough-in at this point. Do not run them while sheet rocking. They are not construction heaters. Once everything is done, fire them up. Otherwise wrap them in plastic to keep all the construction debris out of them.

Sorry - I should have qualified - only on the back wall for the outdoor units, with no "chase" or lineset visible on the side walls of the exterior.
As for rough in, is it just a matter of running wire and the units are then screwed to the studs? Thinking 10 gauge would be plenty correct?

 

[scanchain]

I had a minisplit system installed in my basement. You would want to pre-run the wires to the location where you want to place the outside unit. 10/2 would be plenty, but you might want to check the specs for the system you are interested in buying just to be sure. The air handlers tap its power from the outside unit. Mine typically uses 14/3 wires.

The air handler come with a mounting plate. You screw the plate onto the studs (over drywall) and then you hang the air handler on the plate.

 

[yeldogt]

Typically the lines and wires are put in place w/ a small section of drywall on the wall and the units mounting plate installed.

After all the insulation and the drywall is in place you hook up the unit ...

the small section of drywall is large enough to properly "mud in" but no so big to making insulation a problem

 

[justinjoyal]

48x30, insulated, in VA..

You dont need two of those ! Only one unit will be plenty..

 

[jpcjguy]

48x30, insulated, in VA..

You dont need two of those ! Only one unit will be plenty..

Yeah - so how do you size these properly? I have a buddy that was recommended twin 24K for his 42x30 and I am a little larger.

I did the ecomfort.com calculator with fair insulation and the building specs and it came up with this:

Cooling Load:
11,300 BTU/hr

Heating Load:
26,500 BTU/hr

 

[ambenz]

I have found my 12k IN 660square footprint would take all night running to get to setpoint and would struggle to maintain setpoint during the day, but it would. But I am in the upper midwest during August, the hottest month. So you have to think how you are going to use you AC unit and the garage. Do you want low humidity from March to October, or just run it to drop humidity when you want to work in the shop. For me, I would rather have a huge unit to spot cool a space within an hour. But, for maintaining a setpoint 24/7 for an extended period of time, in your southern location during the hottest days, you could get away with duel mini's. Cost of electricity to run for extended periods vs spot cool for short times. Will it save you the cost of electricity in the long run?

 

[Jackfre]

Justin may well be correct on the sizing. However, you have a lot of cubes in that space and will have a more even temp throughout the space with two evaps working together to circulate the air.

 

[mobetta]

whats the plan for the attic space?
Id prolly go with a 9-12k up there and a 24 k downstairs
and ceiling fan in that peak

 

[jpcjguy]

whats the plan for the attic space?
Id prolly go with a 9-12k up there and a 24 k downstairs
and ceiling fan in that peak

Right now the upstairs is just storage but will be drywalled. Since I am insulating the outer shell of the building, there will be no insulation in the floor joists between the floors. The thought is if I do use that for something down the road, I would get a dedicated 9-12k unit for that space.
So you are thinking a single 24k for downstairs? I also will have a ceiling fan in the peak of the lift bay to circulate the air. Bought one of these cool mounting boxes that fit at the peak: https://www.amazon.com/Arlington-Industries-FB900-1-Mounting-Cathedral/dp/B002W6ZOYC

 

[Jackfre]

I would suggest that if the 24 is to be under the mezzanine that you cut some registers thru that floor. Don’t put them right over the mini split as you don’t want dust/dirt settling on the unit. Cut them off to the sides. This will allow much better air circulation within the space. I always use the straw and a glass of water analogy on this. Put the straw in a glass of water and finger over the straw and you can lift the water out of the glass. Remove your finger and the water flows. Air is a fluid. Give it a path and it will move.

 

[jpcjguy]

So does anyone have any feedback or reviews of the actual Mitsubishi units?

 

[justinjoyal]

Yeah - so how do you size these properly? I have a buddy that was recommended twin 24K for his 42x30 and I am a little larger.

I did the ecomfort.com calculator with fair insulation and the building specs and it came up with this:

Cooling Load:
11,300 BTU/hr

Heating Load:
26,500 BTU/hr

Well, you size according to the (proper) load calculations.

If you really need under a ton of cooling, why would you put 4 in ?

If heating is more important you can size accordingly, make sure you get the performance data for your unit(s).