Mini Split Advice

[ShawnAM]

Hello,

I am looking into adding a mini-split to my garage. Primary purpose is for cooling in the summer. I am in Phoenix, AZ so it gets real hot.

Garage is poorly insulated in that I don't think there is anything in the walls and I know for sure none above the ceiling. However, I do have some styrofoam panels on the backside of the garage door. Its a two car garage but probably just under 400 sq. ft. Ceiling is about 9 or 10 feet high.

I am wondering if there are any brands that do better with cooling in hot climates. I read a lot about heating in cold weather but there is none of that here.

I have been considering a 18k btu 20 seer Mitsubishi, this one: MSZ-GL18NA-U1 / MUZ-GL18NA-U1

Any thoughts or input from the experts here?

Thanks!

 

[Raisedonadeere]

As far as I can tell all the brands give you the BTU they are rated. The higher the seer the less energy to do that. You cannot get around needing to know what btu per hour is needed unless you want to try different sizes which of course you don’t want to do. Maybe some one with a garage meeting your description has a working setup you can duplicate. I put a 18k window unit I had in a 2 car garage in Alabama and worked on my cars in comfort. On some very hot days, but only used occasionally. A smaller unit probably would have been better if on all the time.

 

[PoorOwner]

That mitsubishi works very good and is one of my favorites.
It is a bigger body model and have more surface area than other 18K

As for the garage is it attached? if attached, the wall joining the house it should have insulation on that attached wall. Other 2 wall you may consider adding insulation.

The biggest issue is going to be the garage door, if it is just a single layer, steel door and you just put foam boards on it I am afraid it will not work too well.
I have seen a big improvement after putting 2 sided steel insulated door, get all the weather stripping so there is almost no gaps. It is a very good investment to keep the temperature without leaking all out.

 

[chinboys]

I got a quick lesson about "air conditioning" back when I was going to college in Tucson back in the 80's.
Refrigeration is used in Arizona to dehumidify moisture from water in the air.
Air conditioning, aka swamp cooling, was to inject humidity into the dry hot air to cool it down.
I recalled Phoenix being in a valley and it gets hotter as a result if the wind does blow through or if the summer monsoon rains in the PM don't happen.

Yes, refrigeration will work as the air handler will pass hot dry air across the cold evaporator coil but with very little condensate.
I would definitely pick a high SEER unit even though you are getting "cheap" power from the dams up north and the nuclear plants to your west.

 

[justinjoyal]

I would add insulation first and then size your mini split accordingly. Better comfort, more efficient.

Either way, try www.loadcalc.net for sizing.

 

[Kaizen]

I would add insulation first and then size your mini split accordingly. Better comfort, more efficient.

Either way, try www.loadcalc.net for sizing.

Ditto. With proper insulation you could get away with a 12k. I bet the difference in money is what insulating will cost.

 

[ShawnAM]

Thanks for the responses!

To answer a few questions, yes the garage is attached to the house but really only about 2/3 of the wall is shared with the interior. Therefore, the builders left insulation out of the area of the wall not shared with the interior of the house.

Also, my garage door is just a simple single sided side metal door. What do think about adding an layer of the mylar type heat reflective "stuff" on top of the foam boards? I think one side currently has it already but other side is bare foam.

I am not sure about adding insulation to the walls. As I understand, this will either require me removing the drywall or hiring a company to spray in foam or blow in loose fill. I would like to avoid either option if at all possible. If I were converting the garage to live-in room it might be different. But I am just trying to be able to work in garage during the summer weekends and evening and not die a heat related death.

But I can definitely insulate the ceiling above. Any suggestions as to whether I should use the blown in insulation or the roll out type there?

 

[dcg9381]

I would definitely pick a high SEER unit even though you are getting "cheap" power from the dams up north and the nuclear plants to your west.

Why? It's a "sometimes" use case (garage), power is cheap in this case. Going 16 SEER to 20+ SEER - it's gonna take a lot of power use to pay that back.

 

[ShawnAM]

So I had a HVAC company come out and give me a quote for an install. They said a 1-ton unit (12K) would be sufficient. The problem is they want $3799 to install a 12k 18 SEER unit. I priced out everything I would need to do the install myself (the unit, parts, tools, etc.) and come to about 2-grand for a 12k 21 SEER unit.

I have done a fair amount of research on the install process and think I can handle it. The problem is I will be without any type of warranty. My question is, for a Mitsubishi unit, is the extra warranty worth the extra 1800 or so I would be spending for the pro install and a slightly less efficient unit? I could essentially buy another mini split for less than that.

 

[dcg9381]

So I'm in-process of installing 2 x 24k BTU Daikin units.
Total cost for these units, pre-built lines, etc - with heat pumps was about $2600 all in. They are only 16 SEER.

Depending on your use case - how often you use the garage, you may want to consider what you are spending in additional SEER and payback. I'd certainly use a higher SEER unit in garage where it was running all the time... I am 100% for high efficiency - where it makes sense. And I'm not sure that "sometimes" use in a poorly insulated garage makes sense. To me, it makes more sense to use a lower cost, large unit that can quickly cool the garage. However, if you're going to cool the garage all the time, a high SEER unit makes sense.
75% of your heat/cool loss is going to be through that roof - consider spending the money on foam insulation...

Like you, estimates on professional install of these things easily doubled or tripled the costs. That is, for the cost of a professional install, I can replace the units between 1-2 times each.

If you have DIY warranty concerns, Mr. Cool seems to have units that are warrantied without the requirement of a certified installer. You pay a little more for the privilege, but not as much as having an installer do it.

The other option is offering cash for someone to provision the units for you and inspect your install per-refrigerant.

The only tools I had to buy were an adapter for the line evacuation and crows-foot wrenches for my torque wrench. I do own the vacuum pump.

 

[ShawnAM]

That is, for the cost of a professional install, I can replace the units between 1-2 times each.

This is exactly what I was thinking! I am really leaning toward just installing myself.

Did your line-set come pre-flared? I am wondering about the about the quality of pre-flared lines or if I will need a flaring tool also.

Also saw a guy selling locally a nitrogen bottle with regulator so might scoop that up this weekend.

 

[jjrbus]

This is exactly what I was thinking! I am really leaning toward just installing myself.

Did your line-set come pre-flared? I am wondering about the about the quality of pre-flared lines or if I will need a flaring tool also.

Also saw a guy selling locally a nitrogen bottle with regulator so might scoop that up this weekend.

I DIY 3 Daikin mini splits in my house. Installation is not rocket science but most mini failures are due to improper installation. I had a vacuum pump and some experience playing with car AC and I still spent $500 on tools!

The bulk of the online install videos are very poor and sometimes just plain wrong!

I went into this eyes wide open, I am at the mercy of where I bought the minis and likely will not get a warranty claim. Although did get an evaporator replaced under warranty before I installed it. I spent $7000 less than my lowest bid so can afford to throw a unit out and replace if needed.

There are some good videos around, I like this one. I also went with Daikin because of price point, available parts and online info.

http://https://www.youtube.com/watch?v=o6WwpAZ-r9I

 

[jjrbus]

This is exactly what I was thinking! I am really leaning toward just installing myself.

Did your line-set come pre-flared? I am wondering about the about the quality of pre-flared lines or if I will need a flaring tool also.

Also saw a guy selling locally a nitrogen bottle with regulator so might scoop that up this weekend.

2 of 4 of the preflared lines failed the flair gauge, plus the nuts on pre flares are too lightweight. These are under 500+ psi and will expand and contract many thousands of times over their lifetime.

 

[ShawnAM]

2 of 4 of the preflared lines failed the flair gauge, plus the nuts on pre flares are too lightweight. These are under 500+ psi and will expand and contract many thousands of times over their lifetime.

Ah, so what I am hearing is be prepared to cut off the flares and put on my own nuts and re-flare.

With that said it would probably be better (and cheaper) to just buy the line set from local supply shop un-flared and just do it right the first time.

 

[mharris2007]

So I had a HVAC company come out and give me a quote for an install. They said a 1-ton unit (12K) would be sufficient. The problem is they want $3799 to install a 12k 18 SEER unit. I priced out everything I would need to do the install myself (the unit, parts, tools, etc.) and come to about 2-grand for a 12k 21 SEER unit.

I have done a fair amount of research on the install process and think I can handle it. The problem is I will be without any type of warranty. My question is, for a Mitsubishi unit, is the extra warranty worth the extra 1800 or so I would be spending for the pro install and a slightly less efficient unit? I could essentially buy another mini split for less than that.

Dude $3800 is cheap, lol!! I'm in So Cal and had multiple shops quote me $4800-5500 for an 18K unit!!!!!!

I told them to all pound sand, and ended up buying everything from alpine home air, installed it all myself, hired an electrician for the 220v circuit ($200) and paid my friend from church ($200) to vac it down and release the refrigerant. He tried to refuse payment but I insisted. So all it the whole project with line set cover, etc cost me $1800. So I saved $3000-4000 dollars by diy'ing. Craziness in so cal dude. The alpine home air guys are really good, knowledgeable and have great customer service. Highly recommended. The units they sell are gree. Mine's been in 2 years no with zero problems.

 

[mharris2007]

Ah, so what I am hearing is be prepared to cut off the flares and put on my own nuts and re-flare.

With that said it would probably be better (and cheaper) to just buy the line set from local supply shop un-flared and just do it right the first time.

Yes this is 100% true. I cut off the flares from the stock line set and redid them. You have to cut the line set down to size anyway, so one end you'll have to re do no matter what. I invested in the best flaring tool after allot of research and loved it. It's this one: https://www.amazon.com/dp/B002SB5RMA/?tag=atomicindus08-20

Worked like a charm.

 

[jjrbus]

Ah, so what I am hearing is be prepared to cut off the flares and put on my own nuts and re-flare.

With that said it would probably be better (and cheaper) to just buy the line set from local supply shop un-flared and just do it right the first time.

From what I read the pre made line sets can be of questionable quality copper, even some with copper spliced to aluminum tubing.

The first one I installed I ordered the lineset with the unit. The second one I found linesets made with US produced copper. The flairs were still not much good and the nuts were too light. But cheaper than buying locally! US produced copper is marked!

I will add a disclaimer, I bought the Daikin units and the flair nuts were much heavier than the premade linsets. Buying off brand cheap minis they may have light flair nuts on them?