Sizing a Mitsubishi mini split for a 3 car garage

[LADyver]

We live in Southern California, not quite coastal, but not quite inland so we get a few hot spells here and there. We are in a time crunch with other contractors and are having issues getting quotes for a mini-split system. The one and only quote we have is for a PLA-A24BA4 (24,000 BTU) and I was shocked because I thought we could get away with a 14,000BTU in our 3 car garage (which will be fully insulated, 20x30x8.5' H, no windows, insulated garage door). I'm not sure if we're being taken for a ride or if that's the best unit for our garage. We don't need it to be an icebox, just need efficiency. Thoughts? Quote price was $6200 installed.......

 

[LADyver]

I guess my main question now is whether or not the system is oversized for the 600 sq ft space it will be in. I know an oversized unit is a bad thing....we need to make the decision on it today.

 

[Jinks]

There are several websites that have calculators for that very purpose. I'm guessing that for garage use (casual, just to make working more comfortable) you can use 15,000 to 18,000 BTU. I have 12,000 in about 500 sq. ft. I found during my contact with A/C contractors they typically figured the sizing as if it were living space. The concept that it didn't need to be 76 deg. at all times was just foreign to them.

 

[dodriven]

Dyver, I have the 2Ton (24k) Mitsubishi unit in my 440 sqft garage. I have 9.5' ceilings and the garage is brick, framing, and sheetrock with no insulation period. I am in central Texas and even in the summer it can maintain icebox temps with ease. I think the general rule of thumb for a well insulated space was 1 ton (12k) for every 400 sqft.

I would guess that the smaller unit would be more than up to the task for your needs.

 

[LADyver]

Perfect.....thanks for the quick responses! When I questioned the sizing the sales guy said he was so certain of the 24,000 unit that he would give it to us for the price of the lower BTU unit. Sales pitch? Probably, but I just wanted to make sure he wasn't waaaaay oversizing it to the point it wouldn't work well.

Thanks!

 

[Jagmandave]

I live in Kansas, where we not only get heat - we get humidity! I Have a similar sq ft garage and bought a window unit that's not only an A/C but also has heat for $600. I framed the unit in and ran the 220V 30amp line myself and it works like gangbusters. I only turn it on when I'm going to be working in there, so it doesn't run all the time and it seems to have had very little impact on my electrical bill. 18K cool and 16K heat, btw.

$6200 for an air conditioner? are you serious?

Another you might consider is a hotel/motel type unit, they also have heat as well as A/C and will easily cool an area this size, also well under $1000.

 

[Jackfre]

In LA, not quite coastal, not quite inland leaves a lot of room for questions

I always undersize, slightly. I'd rather have an AC unit work hard than short cycle. Of course, the Mitsubishi unit you are being quoted is, I assume, an inverter unit so it is variable speed. I'd go with a 15kbtu, at most 18kbtu. I'd also get a quote from a Fujitsu dealer...but I'm biased

 

[LADyver]

Actually, not quite coastal and not quite inland is pretty accurate...lol. Depending on which way the wind blows we can get a thick marine layer, we get a lot of fairly mild days, but in the summer we can get some scorching 100 degree days. It's those hot days that are problematic, we'd like to store more in the garage but we've kept it inside to protect it from the days when the garage turns into an oven. Hopefully the insulation and drywall install will help a little, but we want a little extra insurance.....right now everything is stripped to the studs and construction is slated to start tomorrow (plumbing, electrical), now's the time to do it!!!

 

[Jackfre]

Actually, when you think of it, it is a garage and the doors will be open and you may want to pull it down quickly. That is the only advantage of the bigger unit. Perhaps you will want that capability. I didn't look at the unit specs, but have your dealer provide the low-high heating and cooling ranges for each model you are considering.

I would recommend that you get an Airtec wall mounting bracket and hang the condensing unit on the side of the building. As it is open now you could put some blocking in place now.

 

[Bill1031]

It is hard to oversize a Mitsubishi because of the compressor is a variable drive (Inverter technology) Some facts:

PLAA24BA4 + PUYA24NHA4 Performance:
Cooling Capacity (BTU): 24000
Cooling Capacity Range (BTU): 12,000 - 24,000
Total Input (W): 2,500
SEER: 13.6
Moisture Removal (Pts/hr): 5.1

That unit will do from min 12K Btu to 24K and only 13.6 Seer. I would look at the wall mounted. Easier to install. Higher Seer (19-26 depending on tonnage)
Not sure about your design conditions but in Va when I finish my 24x32 pole garage with 10ft ceiling, insulated walls I am putting in the 15K Heat Pump.
The 6200.00 installed, is a fair price for the 2ton flush mount. Its about 1200.00-1400.00 labor

 

[LADyver]

Thank you so much for your input Bill! I was finding the unit itself for about $4200 (online) but wasn't convinced that we needed such a powerful mini split. Now that you mention the inverter, it makes a little more sense why the company we're dealing with is pushing it. The company guarantees satisfaction and the salesman pushed the larger BTU unit by claiming he'd sell it for the same price as the lower BTU unit. But since he's not giving me the breakdown on the units and labor, it's been difficult (impossible) to figure out what a smaller unit would cost. It seems they want at least $6-$8K per job, but to do that they need to sell the larger units. Since it's through a big box store I'm sure they get a killer deal on bulk purchases of the Mitsubishi units. I'm thinking they would rather install a unit that will make the garage an icebox rather than bring their price down to sell a smaller unit that will just make the garage comfortable. It's easier to slap a guarantee on something that over-performs......

 

[Bill1031]

Ladyver, If it is a Home D store. They do not do the installs themselves. It is farmed out just like Sears, costco, etc. Usually costs more from these people because they get their cut. Find your local HVAC installer and give him your business. He will more than likely be there if you need him or her. All Equipment is ordered through a distributor. If the installer is a dealer for Mitsubishi the cost of the unit is so close it would not matter. Bill

 

[Bill1031]

Ladyver, Another note, 4200.00 online. You need a vacuum pump, gauges, possibly torch, brackets,pad,etc. The units come pre-charged for 25ft on line set. If you need more 410A you have to be certified to buy it. Lots of localities are enforcing putting the locks on the valves. So idiots don't huff the refrigerant! Anyway most of this is all in the labor charge. Also if you buy online and you find someone to do a "side job" and the unit has a problem. Do not expect him to go to the time to get a part and do warranty paperwork for free. Anyway, Good luck and I know you will enjoy the unit as well. Bill

 

[LADyver]

Good news, the HVAC/plumbing guy who is redoing the plumbing in 2 days finally got back to us with a quote for a mini split. He installs Fujitsu which I think is on par with the Mitsubishis, but will get the Mitsubishi for us if we want it. His quote is between $4700 - $5200 for an 18K BTU unit which I think is more reasonable for our situation. And the best thing is, he's just going to do the in-wall prep work so that we don't have to purchase and install a until we're sure we REALLY need one. So, we are going with the local HVAC guy. The big box store did subcontract to another company, and since that company won't give us the breakdown on ANYTHING, we're more comfortable going with our usual guy.

 

[James-W]

I would think a 14,000 BTU is sufficient to cool a 600 square foot insulated garage. You want the unit to run a lot simply because while it is running it is dehumidifying. When it isn't running it isn't dehumidifying so even though the temperature is down, the air still feels damp.

A split system is nice, but you could most likely get by a lot cheaper if you could use portable unit that can be mounted in a wall. Not trying to tell you what to do, just saying it would probably be a lot less expensive that way.