Mini Split Sizing and Placement Assistance

[Lucky Lemon]

Hello Brain Trust –

I would like the collective’s input on the sizing and placement of a mini split system in the garage of our new-to-us house.

We recently moved into a house in North Phoenix that has a 737 square foot garage. Coming from a northern climate I know next to nothing about air conditioning.

Garage – 3 car, one side is tandem. The insulated garage door faces north and has no windows. The north wall is approximately 21 feet wide. The east wall is approximately 43 feet and right now has no windows or doors, but I anticipate a 36-inch man door being installed about 25 feet from the front (north) wall. The south wall is about 12 feet wide and has no windows or doors. The west wall is shared with the house. The ceilings are 10 foot. I found a sticker on the wall that indicated the ceil is R-30. The house was built in 2013 so I believe walls would have average insulation for that time frame and location. There is no shade.

There will be one car that lives in the garage and comes and goes, on average, once per day.

I would like to keep the interior of the garage around 80* if possible, during the summer months.

Thoughts on the BTUs required to cool. I am thinking the Mr. Cool DIY 18,000 BTU system.

Placement – The compressor will be located on the east side of the building. It will be exposed to the sun until about noon and them the building will shade the compressor. As far as the location of the wall unit it could be on the south wall or on the east wall over the to be installed man door. I was anticipating installing over the door, but I was reading the install manual and it was recommended to not install over a door. I do not anticipate heavy usage of the exterior man door as it will mostly used to access the back yard with outdoor equipment (leaf blower, etc.). It could also see more usage than I think. Where would you install the wall unit? Would the entire garage receive adequate cooling if it was installed on the south wall?

Thanks,
LL

 

[dcg9381]

I'm going to get scolded, but you don't have to size ductless like you size traditional AC. They can throttle down and have better controls than just "On/Off".

I don't see any reason not to install it over a door, other than vibration and jarring that would be incurred by opening/closing that door. IE - if you have kids who slam doors, I get it.

The other consideration that might nudge you towards bigger than a traditional unit based on a manual J calculation is that this is not space that will be cooled all the time. So you need some ability to remove that heat more quickly than you'd get out of a properly sized AC.

Cars are big blocks of heat when they've been run and parked, again - more cooling.

I've installed a few of these, various spaces. I'd be looking at around a 18k BTU unit for "reasonably well insulated" 700 sqft, 10' ceiling, AZ. Also remember that they're a bit "directionally" and cool what is in front of them best unless you are flowing air around a bit. Their return is in the same spot, so they don't work the same as you home HVAC. They will cool the garage, but it'll be "coolest" near the unit. Adding a fan to move some air would help even it out.

LL, this is a SWAG, based on being in the same climate, and having installed several in 600-2400 sqft spaces.

 

[shade]

I'd go at least 24k. This also assumes you have good insulation throughout.
I have 48k of cooling in a 900sq ft garage.
I also run servers and 2 refrigerators in there.
If I were to take those heat sources out I'd still use a 36k to have a fast recovery after pulling cars in.
Gilbert here

 

[Jackfre]

I'd stick with the 18 and take what it gives you. I've found that they pretty consistently exceed your expectations.

 

[purduecrew]

Ive got 24K in a 1200sqft garage and its done pretty darn well. i don't think im over/undersized, hot cars and all. However im in middle TN.

 

[Lucky Lemon]

Thanks for the input. seems like 18k is the smallest reasonable, although I think I will try to talk my wife into a 24k.

LL

 

[ItBurnsWhenIPee]

Last place had a shop about that size, metal building with R9 in walls and ceiling. I put in the Mr Cool 24k BTU and it was about right. MAYBE a little undersized.

But a metal building is hotter, and I'm not sure I trust the R9 rating of that insulation.

If I were you, I'd probably do the 24k.