24x38 3 car Garage MiniSplit Sizing

[timgradywy]

We have a 24' x 38' garage (912 sq. ft.) that is attached to our house. It has three solid wood garage doors, one solid wood normal door, and no insulation (except for ~30' that is connected to the house). I plan to insulate the ceiling and walls where possible after installing the mini-split, but even still, the North facing 38' wall holding the garage doors will be virtually uninsulated (it will be all support beams and wood doors). The good news is that only ~12 feet of wall faces south and this wall is shaded.

I have had two contractors quote Mitsubishi mini-splits. One quoted 12 and then 15k BTU (GE15NA2) after I asked for a larger unit. They are adamant that the 15k BTU unit is enough for my garage. The other quoted 24k BTU GE24NA and mentioned that even that might not be enough in the middle of a PA summer without insulation.

Based on what I have seen online, the 12 and 15k BTU are probably too small for an uninsulated garage - especially on very hot or cold days. However, the nice thing is that on mild days, the smaller units can turn down to 3k BTU for dehumidification, whereas the larger unit is stuck at 8k BTU minimum. The 24k BTU seems to be okay overall, but may be oversized after insulation.

I want to be able to work relatively comfortably in the garage all year, and also have good dehumidification year-round to prevent corrosion and improve comfort. I don't mind if the unit is a bit too small initially, so long as once the ceiling is insulated, the garage can maintain 60-80 F even on the worst days (Philadelphia/Baltimore area). What do you guys think?

Thanks.

Tim

 

[Fueler]

I go with #3. More.

 

[justinjoyal]

Roughly 900 sq ft... 12-15k BTU is definitely enough for a well insulated place.

Without insulation, probably more around 18k. Just a quick guess.

Btw, you should get quotes for different brands (sticking with reputable ones).

 

[timgradywy]

So far, it was $5,525 for the MUZ/MSZ-GE24NA and $4,420 for the MUZ/MSZ-GE15NA. This includes running wiring. It seems that there are few dealers around us that still carry anything other than Mitsubishi. Most have tried and eventually dropped other brands.

Tim

 

[justinjoyal]

I dont know about the US market, but things are almost always cheaper in the US than here in Quebec/Canada...

Around here, you get a good 24k BTU from a reputable company (Fujitsu, for example) with full 10 yrs warranty for roughly 3400$ depending on the kind of installation/work needed. And that's canadian dollars.

I know Mitsubishis are overpriced, but to me 5525$US is plain crazy...

 

[timgradywy]

I agree that it's high. Those units go for ~$2300 online, so that would be $3200 in installation costs! I can't imagine that installation takes more than a day or material costs are that much. I have debated doing it myself, especially since I have an AC manifold and vacuum pump set.

This is exactly when we put in a Cummins 20 kW generator, I bought it online, did the physical installation myself, and hired a contractor to do the electrical. Local Cummins reps. were quoting ~$20k installed for a $5,500 generator... We came out of it for well under $10k installed and that included all permitting, fees, and redoing most of our solar and CB panel input wiring. Of course you could get a Generac installed for $8-9k, but I didn't want a Generac.

Tim

 

[justinjoyal]

Some installers are simply too money hungry and people fall for it because they figure more money = more quality, which is definitely not always true.

 

[fastjohnny]

I agree that it's high. Those units go for ~$2300 online, so that would be $3200 in installation costs! I can't imagine that installation takes more than a day or material costs are that much. I have debated doing it myself, especially since I have an AC manifold and vacuum pump set.

This is exactly when we put in a Cummins 20 kW generator, I bought it online, did the physical installation myself, and hired a contractor to do the electrical. Local Cummins reps. were quoting ~$20k installed for a $5,500 generator... We came out of it for well under $10k installed and that included all permitting, fees, and redoing most of our solar and CB panel input wiring. Of course you could get a Generac installed for $8-9k, but I didn't want a Generac.

Tim

Self install, but get a micron gauge. The ac manifold is not sufficient for monitoring vacuum/moisture.

 

[sands35]

You might want to do the math on the cost of insulation+15k unit vs the 24k unit.

Insulation will pay for itself in running costs eventually - especially in the winter.

 

[timgradywy]

Insulation is step 2. The ceiling/roof has room for significant insulation. The walls have some room, but they're not thick enough for anything too significant.

Tim

 

[sands35]

R13 is just fine for wall. Make sure the garage door is well sealed to the frame when closed. For humidity control, it is better for a slightly smaller unit that will run more often, then a bigger unit that won't.

But if insulation is already in your budget.

 

[timgradywy]

I have had three local contractors come out to do quotes. Still waiting on the quote from the third, but so far I am not convinced that paying someone to install a mini-split is in my best interest.

Currently looking at two (possibly three) separate mini-splits. The Friedrich Breeze BR1224W3A (24k BTU) unit, and a Caribou 18k BTU inverter unit. I have also considered Caribou's 12k BTU 115 V unit, though I suspect that I would need two of them, one on each wall 38' apart in the garage.

The Friedrich would be much more tempting if it had better SEER and HSPF ratings (17.8 / 7.8). That is not much better than a PTHP... The great thing about the Caribou is that their SEER and HSPF ratings (21 / 10.09) are very similar to the Mitsubishi's and Daikins that I was looking at. The downside is that there is very sparse detailed technical information on these units.
http://www.caribouac.com

These units all use a quick connect fitting for the AC and do not require purging or leak testing. All are under $2k online.

Tim

 

[going4speed]

Just finished last weekend with installing my daikin 18k. Now I went above and beyond on the install and still dont see where the two quotes I got came from money wise. I bought the unit for 1400. The two quotes I received were 3950 and 4200. A friend who is an ac tech is going to do the vacuum and start up for me.

 

[timgradywy]

I went with the Friedrich Breeze 24k btu unit. Installed myself, total cost including wiring and wood for mounting was well under $2k. Super easy to do, the inverter really keeps power consumption down, and the unit is more than enough in the middle of winter or summer. The install was ridiculously easy.

Tim

 

[mpire]

I have a 1.5 ton unit in my 3 car garage and while it would be more than enough for an inside room of the same size, the garage door seals are not so great and the large sun surface makes the AC unit really work to cool it down out there.

I would go with a larger unit if were going to do it again.

 

[Falcon67]

I can keep my place nice with about 19K but that is split between two rooms (24x28 - 11K, 12x24 - 8K). I have one 16' metal door that faces south. It's insulated with cut pieces of 1/2 foam which does surprisingly well at blocking heat and cold transfer. If I was putting in a mini to cover a 38~40 long box, I'd as a minimum use a 24K and IMHO better would be splitting that 24K into a 12K on each end. Both my "winder shakers" can blow air 20' which make a big difference in how they cool the space.

 

[Git]

I installed a Mr Slim that I purchased from eComfort. I installed it myself and then paid a Mitsubishi contractor to come out and perform the start-up service ($300) to maintain the warranty

All told I have just over $4,400 into it. Mr Slim 24k outdoor unit with an 18k and 6k indoor units. Note - I can still hook up a 3rd indoor unit if I want to.

If you have any questions about what unit to get - I would suggest you contact eComfort. They have a free service where one of their in-house 'engineers' will look over what you need and make a recommendation. Here is a link to their worksheet:

http://www.ecomfort.com/manuals/eComfortSizingWorksheetandInstructions.pdf

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